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Overview
Comment:Merge experimental changes into trunk.
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SHA1:aa092ac928dc19bd356d25a1dfd3f432dc145ce6
User & Date: dan 2010-08-11 06:04:19
Context
2010-08-11
06:14
Fix memory allocation in proxy locking so that it works with SQLITE_MEMDEBUG. check-in: f854cbe0 user: drh tags: trunk
06:04
Merge experimental changes into trunk. check-in: aa092ac9 user: dan tags: trunk
2010-08-10
15:46
Fix a bug in pager.c causing it to omit the xSync() call required following a hot-journal rollback. Closed-Leaf check-in: 42ba43ac user: dan tags: experimental
07:12
Changes to debugging code in mutex_unix.c and mutex_w32.c to make an assert() statement threadsafe. check-in: e82e32bd user: dan tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/os_unix.c.

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  unsigned char eFileLock;            /* The type of lock held on this fd */
  int lastErrno;                      /* The unix errno from last I/O error */
  void *lockingContext;               /* Locking style specific state */
  UnixUnusedFd *pUnused;              /* Pre-allocated UnixUnusedFd */
  int fileFlags;                      /* Miscellanous flags */
  const char *zPath;                  /* Name of the file */
  unixShm *pShm;                      /* Shared memory segment information */

#if SQLITE_ENABLE_LOCKING_STYLE
  int openFlags;                      /* The flags specified at open() */
#endif
#if SQLITE_ENABLE_LOCKING_STYLE || defined(__APPLE__)
  unsigned fsFlags;                   /* cached details from statfs() */
#endif
#if OS_VXWORKS
................................................................................
  while( amt>0 && (wrote = seekAndWrite(pFile, offset, pBuf, amt))>0 ){
    amt -= wrote;
    offset += wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  SimulateIOError(( wrote=(-1), amt=1 ));
  SimulateDiskfullError(( wrote=0, amt=1 ));

  if( amt>0 ){
    if( wrote<0 ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      pFile->lastErrno = 0; /* not a system error */
      return SQLITE_FULL;
    }
  }

  return SQLITE_OK;
}

#ifdef SQLITE_TEST
/*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occurring at the right times.
................................................................................
  return rc;
}

/*
** Truncate an open file to a specified size
*/
static int unixTruncate(sqlite3_file *id, i64 nByte){

  int rc;
  assert( id );
  SimulateIOError( return SQLITE_IOERR_TRUNCATE );










  rc = ftruncate(((unixFile*)id)->h, (off_t)nByte);
  if( rc ){
    ((unixFile*)id)->lastErrno = errno;
    return SQLITE_IOERR_TRUNCATE;
  }else{
#ifndef NDEBUG
    /* If we are doing a normal write to a database file (as opposed to
    ** doing a hot-journal rollback or a write to some file other than a
    ** normal database file) and we truncate the file to zero length,
    ** that effectively updates the change counter.  This might happen
    ** when restoring a database using the backup API from a zero-length
    ** source.
    */
    if( ((unixFile*)id)->inNormalWrite && nByte==0 ){
      ((unixFile*)id)->transCntrChng = 1;
    }
#endif

    return SQLITE_OK;
  }
}

................................................................................
/*
** Handler for proxy-locking file-control verbs.  Defined below in the
** proxying locking division.
*/
static int proxyFileControl(sqlite3_file*,int,void*);
#endif


















































/*
** Information and control of an open file handle.
*/
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = ((unixFile*)id)->eFileLock;
      return SQLITE_OK;
    }
    case SQLITE_LAST_ERRNO: {
      *(int*)pArg = ((unixFile*)id)->lastErrno;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SIZE_HINT: {
#if 0 /* No performance advantage seen on Linux */
      sqlite3_int64 szFile = *(sqlite3_int64*)pArg;
      unixFile *pFile = (unixFile*)id;
      ftruncate(pFile->h, szFile);
#endif
      return SQLITE_OK;
    }
#ifndef NDEBUG
    /* The pager calls this method to signal that it has done
    ** a rollback and that the database is therefore unchanged and
    ** it hence it is OK for the transaction change counter to be
    ** unchanged.
    */







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  unsigned char eFileLock;            /* The type of lock held on this fd */
  int lastErrno;                      /* The unix errno from last I/O error */
  void *lockingContext;               /* Locking style specific state */
  UnixUnusedFd *pUnused;              /* Pre-allocated UnixUnusedFd */
  int fileFlags;                      /* Miscellanous flags */
  const char *zPath;                  /* Name of the file */
  unixShm *pShm;                      /* Shared memory segment information */
  int szChunk;                        /* Configured by FCNTL_CHUNK_SIZE */
#if SQLITE_ENABLE_LOCKING_STYLE
  int openFlags;                      /* The flags specified at open() */
#endif
#if SQLITE_ENABLE_LOCKING_STYLE || defined(__APPLE__)
  unsigned fsFlags;                   /* cached details from statfs() */
#endif
#if OS_VXWORKS
................................................................................
  while( amt>0 && (wrote = seekAndWrite(pFile, offset, pBuf, amt))>0 ){
    amt -= wrote;
    offset += wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  SimulateIOError(( wrote=(-1), amt=1 ));
  SimulateDiskfullError(( wrote=0, amt=1 ));

  if( amt>0 ){
    if( wrote<0 ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      pFile->lastErrno = 0; /* not a system error */
      return SQLITE_FULL;
    }
  }

  return SQLITE_OK;
}

#ifdef SQLITE_TEST
/*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occurring at the right times.
................................................................................
  return rc;
}

/*
** Truncate an open file to a specified size
*/
static int unixTruncate(sqlite3_file *id, i64 nByte){
  unixFile *pFile = (unixFile *)id;
  int rc;
  assert( pFile );
  SimulateIOError( return SQLITE_IOERR_TRUNCATE );

  /* If the user has configured a chunk-size for this file, truncate the
  ** file so that it consists of an integer number of chunks (i.e. the
  ** actual file size after the operation may be larger than the requested
  ** size).
  */
  if( pFile->szChunk ){
    nByte = ((nByte + pFile->szChunk - 1)/pFile->szChunk) * pFile->szChunk;
  }

  rc = ftruncate(pFile->h, (off_t)nByte);
  if( rc ){
    pFile->lastErrno = errno;
    return SQLITE_IOERR_TRUNCATE;
  }else{
#ifndef NDEBUG
    /* If we are doing a normal write to a database file (as opposed to
    ** doing a hot-journal rollback or a write to some file other than a
    ** normal database file) and we truncate the file to zero length,
    ** that effectively updates the change counter.  This might happen
    ** when restoring a database using the backup API from a zero-length
    ** source.
    */
    if( pFile->inNormalWrite && nByte==0 ){
      pFile->transCntrChng = 1;
    }
#endif

    return SQLITE_OK;
  }
}

................................................................................
/*
** Handler for proxy-locking file-control verbs.  Defined below in the
** proxying locking division.
*/
static int proxyFileControl(sqlite3_file*,int,void*);
#endif

/* 
** This function is called to handle the SQLITE_FCNTL_SIZE_HINT 
** file-control operation.
**
** If the user has configured a chunk-size for this file, it could be
** that the file needs to be extended at this point. Otherwise, the
** SQLITE_FCNTL_SIZE_HINT operation is a no-op for Unix.
*/
static int fcntlSizeHint(unixFile *pFile, i64 nByte){
  if( pFile->szChunk ){
    i64 nSize;                    /* Required file size */
    struct stat buf;              /* Used to hold return values of fstat() */
   
    if( fstat(pFile->h, &buf) ) return SQLITE_IOERR_FSTAT;

    nSize = ((nByte+pFile->szChunk-1) / pFile->szChunk) * pFile->szChunk;
    if( nSize>(i64)buf.st_size ){
#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
      if( posix_fallocate(pFile->h, buf.st_size, nSize-buf.st_size) ){
        return SQLITE_IOERR_WRITE;
      }
#else
      /* If the OS does not have posix_fallocate(), fake it. First use
      ** ftruncate() to set the file size, then write a single byte to
      ** the last byte in each block within the extended region. This
      ** is the same technique used by glibc to implement posix_fallocate()
      ** on systems that do not have a real fallocate() system call.
      */
      int nBlk = buf.st_blksize;  /* File-system block size */
      i64 iWrite;                 /* Next offset to write to */
      int nWrite;                 /* Return value from seekAndWrite() */

      if( ftruncate(pFile->h, nSize) ){
        pFile->lastErrno = errno;
        return SQLITE_IOERR_TRUNCATE;
      }
      iWrite = ((buf.st_size + 2*nBlk - 1)/nBlk)*nBlk-1;
      do {
        nWrite = seekAndWrite(pFile, iWrite, "", 1);
        iWrite += nBlk;
      } while( nWrite==1 && iWrite<nSize );
      if( nWrite!=1 ) return SQLITE_IOERR_WRITE;
#endif
    }
  }

  return SQLITE_OK;
}

/*
** Information and control of an open file handle.
*/
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = ((unixFile*)id)->eFileLock;
      return SQLITE_OK;
    }
    case SQLITE_LAST_ERRNO: {
      *(int*)pArg = ((unixFile*)id)->lastErrno;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_CHUNK_SIZE: {
      ((unixFile*)id)->szChunk = *(int *)pArg;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SIZE_HINT: {
      return fcntlSizeHint((unixFile *)id, *(i64 *)pArg);

    }
#ifndef NDEBUG
    /* The pager calls this method to signal that it has done
    ** a rollback and that the database is therefore unchanged and
    ** it hence it is OK for the transaction change counter to be
    ** unchanged.
    */

Changes to src/os_win.c.

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  HANDLE h;               /* Handle for accessing the file */
  unsigned char locktype; /* Type of lock currently held on this file */
  short sharedLockByte;   /* Randomly chosen byte used as a shared lock */
  DWORD lastErrno;        /* The Windows errno from the last I/O error */
  DWORD sectorSize;       /* Sector size of the device file is on */
  winShm *pShm;           /* Instance of shared memory on this file */
  const char *zPath;      /* Full pathname of this file */

#if SQLITE_OS_WINCE
  WCHAR *zDeleteOnClose;  /* Name of file to delete when closing */
  HANDLE hMutex;          /* Mutex used to control access to shared lock */  
  HANDLE hShared;         /* Shared memory segment used for locking */
  winceLock local;        /* Locks obtained by this instance of winFile */
  winceLock *shared;      /* Global shared lock memory for the file  */
#endif
................................................................................
*****************************************************************************/
#endif /* SQLITE_OS_WINCE */

/*****************************************************************************
** The next group of routines implement the I/O methods specified
** by the sqlite3_io_methods object.
******************************************************************************/





































/*
** Close a file.
**
** It is reported that an attempt to close a handle might sometimes
** fail.  This is a very unreasonable result, but windows is notorious
** for being unreasonable so I do not doubt that it might happen.  If
................................................................................
  }
#endif
  OSTRACE(("CLOSE %d %s\n", pFile->h, rc ? "ok" : "failed"));
  OpenCounter(-1);
  return rc ? SQLITE_OK : SQLITE_IOERR;
}

/*
** Some microsoft compilers lack this definition.
*/
#ifndef INVALID_SET_FILE_POINTER
# define INVALID_SET_FILE_POINTER ((DWORD)-1)
#endif

/*
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/
static int winRead(
  sqlite3_file *id,          /* File to read from */
  void *pBuf,                /* Write content into this buffer */
  int amt,                   /* Number of bytes to read */
  sqlite3_int64 offset       /* Begin reading at this offset */
){
  LONG upperBits = (LONG)((offset>>32) & 0x7fffffff);
  LONG lowerBits = (LONG)(offset & 0xffffffff);
  DWORD rc;
  winFile *pFile = (winFile*)id;
  DWORD error;
  DWORD got;


  assert( id!=0 );
  SimulateIOError(return SQLITE_IOERR_READ);
  OSTRACE(("READ %d lock=%d\n", pFile->h, pFile->locktype));
  rc = SetFilePointer(pFile->h, lowerBits, &upperBits, FILE_BEGIN);

  if( rc==INVALID_SET_FILE_POINTER && (error=GetLastError())!=NO_ERROR ){
    pFile->lastErrno = error;
    return SQLITE_FULL;
  }
  if( !ReadFile(pFile->h, pBuf, amt, &got, 0) ){
    pFile->lastErrno = GetLastError();
    return SQLITE_IOERR_READ;
  }
  if( got==(DWORD)amt ){
    return SQLITE_OK;
  }else{
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.
*/
static int winWrite(
  sqlite3_file *id,         /* File to write into */
  const void *pBuf,         /* The bytes to be written */
  int amt,                  /* Number of bytes to write */
  sqlite3_int64 offset      /* Offset into the file to begin writing at */
){
  LONG upperBits = (LONG)((offset>>32) & 0x7fffffff);
  LONG lowerBits = (LONG)(offset & 0xffffffff);
  DWORD rc;
  winFile *pFile = (winFile*)id;
  DWORD error;
  DWORD wrote = 0;

  assert( id!=0 );

  SimulateIOError(return SQLITE_IOERR_WRITE);
  SimulateDiskfullError(return SQLITE_FULL);

  OSTRACE(("WRITE %d lock=%d\n", pFile->h, pFile->locktype));
  rc = SetFilePointer(pFile->h, lowerBits, &upperBits, FILE_BEGIN);
  if( rc==INVALID_SET_FILE_POINTER && (error=GetLastError())!=NO_ERROR ){
    pFile->lastErrno = error;
    if( pFile->lastErrno==ERROR_HANDLE_DISK_FULL ){
      return SQLITE_FULL;
    }else{
      return SQLITE_IOERR_WRITE;
    }





  }
  assert( amt>0 );
  while(
     amt>0
     && (rc = WriteFile(pFile->h, pBuf, amt, &wrote, 0))!=0
     && wrote>0
  ){
    amt -= wrote;
    pBuf = &((char*)pBuf)[wrote];



  }
  if( !rc || amt>(int)wrote ){

    pFile->lastErrno = GetLastError();





    if( pFile->lastErrno==ERROR_HANDLE_DISK_FULL ){
      return SQLITE_FULL;
    }else{
      return SQLITE_IOERR_WRITE;
    }

  }
  return SQLITE_OK;
}

/*
** Truncate an open file to a specified size
*/
static int winTruncate(sqlite3_file *id, sqlite3_int64 nByte){
  LONG upperBits = (LONG)((nByte>>32) & 0x7fffffff);
  LONG lowerBits = (LONG)(nByte & 0xffffffff);
  DWORD dwRet;
  winFile *pFile = (winFile*)id;
  DWORD error;
  int rc = SQLITE_OK;

  assert( id!=0 );
  OSTRACE(("TRUNCATE %d %lld\n", pFile->h, nByte));
  SimulateIOError(return SQLITE_IOERR_TRUNCATE);
  dwRet = SetFilePointer(pFile->h, lowerBits, &upperBits, FILE_BEGIN);
  if( dwRet==INVALID_SET_FILE_POINTER && (error=GetLastError())!=NO_ERROR ){
    pFile->lastErrno = error;
    rc = SQLITE_IOERR_TRUNCATE;
  /* SetEndOfFile will fail if nByte is negative */
  }else if( !SetEndOfFile(pFile->h) ){





    pFile->lastErrno = GetLastError();
    rc = SQLITE_IOERR_TRUNCATE;
  }

  OSTRACE(("TRUNCATE %d %lld %s\n", pFile->h, nByte, rc==SQLITE_OK ? "ok" : "failed"));
  return rc;
}

#ifdef SQLITE_TEST
/*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occuring at the right times.
................................................................................
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = ((winFile*)id)->locktype;
      return SQLITE_OK;
    }
    case SQLITE_LAST_ERRNO: {
      *(int*)pArg = (int)((winFile*)id)->lastErrno;
      return SQLITE_OK;




    }
    case SQLITE_FCNTL_SIZE_HINT: {
      sqlite3_int64 sz = *(sqlite3_int64*)pArg;
      SimulateIOErrorBenign(1);
      winTruncate(id, sz);
      SimulateIOErrorBenign(0);
      return SQLITE_OK;







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  HANDLE h;               /* Handle for accessing the file */
  unsigned char locktype; /* Type of lock currently held on this file */
  short sharedLockByte;   /* Randomly chosen byte used as a shared lock */
  DWORD lastErrno;        /* The Windows errno from the last I/O error */
  DWORD sectorSize;       /* Sector size of the device file is on */
  winShm *pShm;           /* Instance of shared memory on this file */
  const char *zPath;      /* Full pathname of this file */
  int szChunk;            /* Chunk size configured by FCNTL_CHUNK_SIZE */
#if SQLITE_OS_WINCE
  WCHAR *zDeleteOnClose;  /* Name of file to delete when closing */
  HANDLE hMutex;          /* Mutex used to control access to shared lock */  
  HANDLE hShared;         /* Shared memory segment used for locking */
  winceLock local;        /* Locks obtained by this instance of winFile */
  winceLock *shared;      /* Global shared lock memory for the file  */
#endif
................................................................................
*****************************************************************************/
#endif /* SQLITE_OS_WINCE */

/*****************************************************************************
** The next group of routines implement the I/O methods specified
** by the sqlite3_io_methods object.
******************************************************************************/

/*
** Some microsoft compilers lack this definition.
*/
#ifndef INVALID_SET_FILE_POINTER
# define INVALID_SET_FILE_POINTER ((DWORD)-1)
#endif

/*
** Move the current position of the file handle passed as the first 
** argument to offset iOffset within the file. If successful, return 0. 
** Otherwise, set pFile->lastErrno and return non-zero.
*/
static int seekWinFile(winFile *pFile, sqlite3_int64 iOffset){
  LONG upperBits;                 /* Most sig. 32 bits of new offset */
  LONG lowerBits;                 /* Least sig. 32 bits of new offset */
  DWORD dwRet;                    /* Value returned by SetFilePointer() */

  upperBits = (LONG)((iOffset>>32) & 0x7fffffff);
  lowerBits = (LONG)(iOffset & 0xffffffff);

  /* API oddity: If successful, SetFilePointer() returns a dword 
  ** containing the lower 32-bits of the new file-offset. Or, if it fails,
  ** it returns INVALID_SET_FILE_POINTER. However according to MSDN, 
  ** INVALID_SET_FILE_POINTER may also be a valid new offset. So to determine 
  ** whether an error has actually occured, it is also necessary to call 
  ** GetLastError().
  */
  dwRet = SetFilePointer(pFile->h, lowerBits, &upperBits, FILE_BEGIN);
  if( (dwRet==INVALID_SET_FILE_POINTER && GetLastError()!=NO_ERROR) ){
    pFile->lastErrno = GetLastError();
    return 1;
  }

  return 0;
}

/*
** Close a file.
**
** It is reported that an attempt to close a handle might sometimes
** fail.  This is a very unreasonable result, but windows is notorious
** for being unreasonable so I do not doubt that it might happen.  If
................................................................................
  }
#endif
  OSTRACE(("CLOSE %d %s\n", pFile->h, rc ? "ok" : "failed"));
  OpenCounter(-1);
  return rc ? SQLITE_OK : SQLITE_IOERR;
}








/*
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/
static int winRead(
  sqlite3_file *id,          /* File to read from */
  void *pBuf,                /* Write content into this buffer */
  int amt,                   /* Number of bytes to read */
  sqlite3_int64 offset       /* Begin reading at this offset */
){



  winFile *pFile = (winFile*)id;  /* file handle */


  DWORD nRead;                    /* Number of bytes actually read from file */

  assert( id!=0 );
  SimulateIOError(return SQLITE_IOERR_READ);
  OSTRACE(("READ %d lock=%d\n", pFile->h, pFile->locktype));


  if( seekWinFile(pFile, offset) ){

    return SQLITE_FULL;
  }
  if( !ReadFile(pFile->h, pBuf, amt, &nRead, 0) ){
    pFile->lastErrno = GetLastError();
    return SQLITE_IOERR_READ;
  }
  if( nRead<(DWORD)amt ){
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[nRead], 0, amt-nRead);
    return SQLITE_IOERR_SHORT_READ;
  }

  return SQLITE_OK;
}

/*
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.
*/
static int winWrite(
  sqlite3_file *id,               /* File to write into */
  const void *pBuf,               /* The bytes to be written */
  int amt,                        /* Number of bytes to write */
  sqlite3_int64 offset            /* Offset into the file to begin writing at */
){
  int rc;                         /* True if error has occured, else false */


  winFile *pFile = (winFile*)id;  /* File handle */



  assert( amt>0 );
  assert( pFile );
  SimulateIOError(return SQLITE_IOERR_WRITE);
  SimulateDiskfullError(return SQLITE_FULL);

  OSTRACE(("WRITE %d lock=%d\n", pFile->h, pFile->locktype));








  rc = seekWinFile(pFile, offset);
  if( rc==0 ){
    u8 *aRem = (u8 *)pBuf;        /* Data yet to be written */
    int nRem = amt;               /* Number of bytes yet to be written */
    DWORD nWrite;                 /* Bytes written by each WriteFile() call */









    while( nRem>0 && WriteFile(pFile->h, aRem, nRem, &nWrite, 0) && nWrite>0 ){
      aRem += nWrite;
      nRem -= nWrite;
    }

    if( nRem>0 ){
      pFile->lastErrno = GetLastError();
      rc = 1;
    }
  }

  if( rc ){
    if( pFile->lastErrno==ERROR_HANDLE_DISK_FULL ){
      return SQLITE_FULL;


    }
    return SQLITE_IOERR_WRITE;
  }
  return SQLITE_OK;
}

/*
** Truncate an open file to a specified size
*/
static int winTruncate(sqlite3_file *id, sqlite3_int64 nByte){
  winFile *pFile = (winFile*)id;  /* File handle object */
  int rc = SQLITE_OK;             /* Return code for this function */

  assert( pFile );

  OSTRACE(("TRUNCATE %d %lld\n", pFile->h, nByte));
  SimulateIOError(return SQLITE_IOERR_TRUNCATE);

  /* If the user has configured a chunk-size for this file, truncate the
  ** file so that it consists of an integer number of chunks (i.e. the
  ** actual file size after the operation may be larger than the requested
  ** size).
  */
  if( pFile->szChunk ){
    nByte = ((nByte + pFile->szChunk - 1)/pFile->szChunk) * pFile->szChunk;
  }

  /* SetEndOfFile() returns non-zero when successful, or zero when it fails. */
  if( seekWinFile(pFile, nByte) ){
    rc = SQLITE_IOERR_TRUNCATE;
  }else if( 0==SetEndOfFile(pFile->h) ){
    pFile->lastErrno = GetLastError();
    rc = SQLITE_IOERR_TRUNCATE;
  }

  OSTRACE(("TRUNCATE %d %lld %s\n", pFile->h, nByte, rc ? "failed" : "ok"));
  return rc;
}

#ifdef SQLITE_TEST
/*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occuring at the right times.
................................................................................
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = ((winFile*)id)->locktype;
      return SQLITE_OK;
    }
    case SQLITE_LAST_ERRNO: {
      *(int*)pArg = (int)((winFile*)id)->lastErrno;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_CHUNK_SIZE: {
      ((winFile*)id)->szChunk = *(int *)pArg;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SIZE_HINT: {
      sqlite3_int64 sz = *(sqlite3_int64*)pArg;
      SimulateIOErrorBenign(1);
      winTruncate(id, sz);
      SimulateIOErrorBenign(0);
      return SQLITE_OK;

Changes to src/pager.c.

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....
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6156
** associated file-descriptor is returned. FILEHANDLEID() takes an sqlite3_file
** struct as its argument.
*/
#define PAGERID(p) ((int)(p->fd))
#define FILEHANDLEID(fd) ((int)fd)

/*
** The page cache as a whole is always in one of the following

** states:
**
**   PAGER_UNLOCK        The page cache is not currently reading or 
**                       writing the database file.  There is no
**                       data held in memory.  This is the initial
**                       state.
**
**   PAGER_SHARED        The page cache is reading the database.
**                       Writing is not permitted.  There can be
**                       multiple readers accessing the same database
**                       file at the same time.
**
**   PAGER_RESERVED      This process has reserved the database for writing
**                       but has not yet made any changes.  Only one process
**                       at a time can reserve the database.  The original
**                       database file has not been modified so other
**                       processes may still be reading the on-disk
**                       database file.

**
**   PAGER_EXCLUSIVE     The page cache is writing the database.
**                       Access is exclusive.  No other processes or
**                       threads can be reading or writing while one
**                       process is writing.
**

**   PAGER_SYNCED        The pager moves to this state from PAGER_EXCLUSIVE
**                       after all dirty pages have been written to the
**                       database file and the file has been synced to
**                       disk. All that remains to do is to remove or
**                       truncate the journal file and the transaction 
**                       will be committed.

**
** The page cache comes up in PAGER_UNLOCK.  The first time a
** sqlite3PagerGet() occurs, the state transitions to PAGER_SHARED.
** After all pages have been released using sqlite_page_unref(),
** the state transitions back to PAGER_UNLOCK.  The first time
** that sqlite3PagerWrite() is called, the state transitions to
** PAGER_RESERVED.  (Note that sqlite3PagerWrite() can only be
** called on an outstanding page which means that the pager must
** be in PAGER_SHARED before it transitions to PAGER_RESERVED.)
** PAGER_RESERVED means that there is an open rollback journal.
** The transition to PAGER_EXCLUSIVE occurs before any changes
** are made to the database file, though writes to the rollback



































































































































** journal occurs with just PAGER_RESERVED.  After an sqlite3PagerRollback()


** or sqlite3PagerCommitPhaseTwo(), the state can go back to PAGER_SHARED,
** or it can stay at PAGER_EXCLUSIVE if we are in exclusive access mode.

































*/
#define PAGER_UNLOCK      0
#define PAGER_SHARED      1   /* same as SHARED_LOCK */
#define PAGER_RESERVED    2   /* same as RESERVED_LOCK */
#define PAGER_EXCLUSIVE   4   /* same as EXCLUSIVE_LOCK */
#define PAGER_SYNCED      5
























































/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC1(P,D,N,X,E) \
    if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
................................................................................
  Pgno iSubRec;                /* Index of first record in sub-journal */
#ifndef SQLITE_OMIT_WAL
  u32 aWalData[WAL_SAVEPOINT_NDATA];        /* WAL savepoint context */
#endif
};

/*
** A open page cache is an instance of the following structure.
**
** errCode
**
**   Pager.errCode may be set to SQLITE_IOERR, SQLITE_CORRUPT, or
**   or SQLITE_FULL. Once one of the first three errors occurs, it persists
**   and is returned as the result of every major pager API call.  The
**   SQLITE_FULL return code is slightly different. It persists only until the
**   next successful rollback is performed on the pager cache. Also,
**   SQLITE_FULL does not affect the sqlite3PagerGet() and sqlite3PagerLookup()
**   APIs, they may still be used successfully.
**
** dbSizeValid, dbSize, dbOrigSize, dbFileSize
**
**   Managing the size of the database file in pages is a little complicated.
**   The variable Pager.dbSize contains the number of pages that the database
**   image currently contains. As the database image grows or shrinks this
**   variable is updated. The variable Pager.dbFileSize contains the number
**   of pages in the database file. This may be different from Pager.dbSize
**   if some pages have been appended to the database image but not yet written
**   out from the cache to the actual file on disk. Or if the image has been
**   truncated by an incremental-vacuum operation. The Pager.dbOrigSize variable
**   contains the number of pages in the database image when the current
**   transaction was opened. The contents of all three of these variables is
**   only guaranteed to be correct if the boolean Pager.dbSizeValid is true.
**
**   TODO: Under what conditions is dbSizeValid set? Cleared?
**
** changeCountDone
**
**   This boolean variable is used to make sure that the change-counter 
**   (the 4-byte header field at byte offset 24 of the database file) is 
**   not updated more often than necessary. 
**
................................................................................
**   The changeCountDone flag is inspected. If it is true, the work of
**   updating the change-counter is omitted for the current transaction.
**
**   This mechanism means that when running in exclusive mode, a connection 
**   need only update the change-counter once, for the first transaction
**   committed.
**
** dbModified
**
**   The dbModified flag is set whenever a database page is dirtied.
**   It is cleared at the end of each transaction.
**
**   It is used when committing or otherwise ending a transaction. If
**   the dbModified flag is clear then less work has to be done.
**
** journalStarted
**
**   This flag is set during a write-transaction after the first 
**   journal-header is written and synced to disk.
**
**   After this has happened, new pages appended to the database 
**   do not need the PGHDR_NEED_SYNC flag set, as they do not need
**   to wait for a journal sync before they can be written out to
**   the database file (see function pager_write()).
**   
** setMaster
**
**   When PagerCommitPhaseOne() is called to commit a transaction, it may
**   (or may not) specify a master-journal name to be written into the 
**   journal file before it is synced to disk.
**
**   Whether or not a journal file contains a master-journal pointer affects 
**   the way in which the journal file is finalized after the transaction is 
**   committed or rolled back when running in "journal_mode=PERSIST" mode.
**   If a journal file does not contain a master-journal pointer, it is
**   finalized by overwriting the first journal header with zeroes. If,
**   on the other hand, it does contain a master-journal pointer, the
**   journal file is finalized by truncating it to zero bytes, just as if
**   the connection were running in "journal_mode=truncate" mode.
**
**   Journal files that contain master journal pointers cannot be finalized
**   simply by overwriting the first journal-header with zeroes, as the
**   master journal pointer could interfere with hot-journal rollback of any
**   subsequently interrupted transaction that reuses the journal file.
**
**   The flag is cleared as soon as the journal file is finalized (either
**   by PagerCommitPhaseTwo or PagerRollback). If an IO error prevents the
**   journal file from being successfully finalized, the setMaster flag
**   is cleared anyway.
**
** doNotSpill, doNotSyncSpill
**
**   When enabled, cache spills are prohibited.  The doNotSpill variable
**   inhibits all cache spill and doNotSyncSpill inhibits those spills that
**   would require a journal sync.  The doNotSyncSpill is set and cleared 
**   by sqlite3PagerWrite() in order to prevent a journal sync from happening 
**   in between the journalling of two pages on the same sector.  The
**   doNotSpill value set to prevent pagerStress() from trying to use
**   the journal during a rollback.
**




** needSync
**
**   TODO: It might be easier to set this variable in writeJournalHdr()
**   and writeMasterJournal() only. Change its meaning to "unsynced data
**   has been written to the journal".


**
** subjInMemory
**
**   This is a boolean variable. If true, then any required sub-journal
**   is opened as an in-memory journal file. If false, then in-memory
**   sub-journals are only used for in-memory pager files.











































































*/
struct Pager {
  sqlite3_vfs *pVfs;          /* OS functions to use for IO */
  u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
  u8 journalMode;             /* On of the PAGER_JOURNALMODE_* values */
  u8 useJournal;              /* Use a rollback journal on this file */
  u8 noReadlock;              /* Do not bother to obtain readlocks */
  u8 noSync;                  /* Do not sync the journal if true */
  u8 fullSync;                /* Do extra syncs of the journal for robustness */
  u8 sync_flags;              /* One of SYNC_NORMAL or SYNC_FULL */
  u8 tempFile;                /* zFilename is a temporary file */
  u8 readOnly;                /* True for a read-only database */
................................................................................
  ** operates.
  **
  ** The 'state' variable is described in more detail along with the
  ** descriptions of the values it may take - PAGER_UNLOCK etc. Many of the
  ** other variables in this block are described in the comment directly 
  ** above this class definition.
  */
  u8 state;                   /* PAGER_UNLOCK, _SHARED, _RESERVED, etc. */
  u8 dbModified;              /* True if there are any changes to the Db */
  u8 needSync;                /* True if an fsync() is needed on the journal */
  u8 journalStarted;          /* True if header of journal is synced */
  u8 changeCountDone;         /* Set after incrementing the change-counter */
  u8 setMaster;               /* True if a m-j name has been written to jrnl */
  u8 doNotSpill;              /* Do not spill the cache when non-zero */
  u8 doNotSyncSpill;          /* Do not do a spill that requires jrnl sync */
  u8 dbSizeValid;             /* Set when dbSize is correct */
  u8 subjInMemory;            /* True to use in-memory sub-journals */
  Pgno dbSize;                /* Number of pages in the database */
  Pgno dbOrigSize;            /* dbSize before the current transaction */
  Pgno dbFileSize;            /* Number of pages in the database file */

  int errCode;                /* One of several kinds of errors */
  int nRec;                   /* Pages journalled since last j-header written */
  u32 cksumInit;              /* Quasi-random value added to every checksum */
  u32 nSubRec;                /* Number of records written to sub-journal */
  Bitvec *pInJournal;         /* One bit for each page in the database file */
  sqlite3_file *fd;           /* File descriptor for database */
  sqlite3_file *jfd;          /* File descriptor for main journal */
................................................................................
#endif

/*
** The maximum legal page number is (2^31 - 1).
*/
#define PAGER_MAX_PGNO 2147483647































#ifndef NDEBUG 
/*
** Usage:
**
**   assert( assert_pager_state(pPager) );



*/
static int assert_pager_state(Pager *pPager){


  /* A temp-file is always in PAGER_EXCLUSIVE or PAGER_SYNCED state. */
  assert( pPager->tempFile==0 || pPager->state>=PAGER_EXCLUSIVE );












  /* The changeCountDone flag is always set for temp-files */


  assert( pPager->tempFile==0 || pPager->changeCountDone );




























































































  return 1;
}

















































#endif

/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
................................................................................
  return rc;
}

/*
** Write a 32-bit integer into a string buffer in big-endian byte order.
*/
#define put32bits(A,B)  sqlite3Put4byte((u8*)A,B)


/*
** Write a 32-bit integer into the given file descriptor.  Return SQLITE_OK
** on success or an error code is something goes wrong.
*/
static int write32bits(sqlite3_file *fd, i64 offset, u32 val){
  char ac[4];
  put32bits(ac, val);
  return sqlite3OsWrite(fd, ac, 4, offset);
}

/*
** The argument to this macro is a file descriptor (type sqlite3_file*).
** Return 0 if it is not open, or non-zero (but not 1) if it is.
**
** This is so that expressions can be written as:
**

**   if( isOpen(pPager->jfd) ){ ...
**
** instead of
**
**   if( pPager->jfd->pMethods ){ ...
*/



#define isOpen(pFd) ((pFd)->pMethods)













/*
** If file pFd is open, call sqlite3OsUnlock() on it.








*/
static int osUnlock(sqlite3_file *pFd, int eLock){
  if( !isOpen(pFd) ){

    return SQLITE_OK;
  }
  return sqlite3OsUnlock(pFd, eLock);









}

/*
** This function determines whether or not the atomic-write optimization
** can be used with this pager. The optimization can be used if:
**
**  (a) the value returned by OsDeviceCharacteristics() indicates that
................................................................................
  **   * When the pager is in no-sync mode. Corruption can follow a
  **     power failure in this case anyway.
  **
  **   * When the SQLITE_IOCAP_SAFE_APPEND flag is set. This guarantees
  **     that garbage data is never appended to the journal file.
  */
  assert( isOpen(pPager->fd) || pPager->noSync );
  if( (pPager->noSync) || (pPager->journalMode==PAGER_JOURNALMODE_MEMORY)
   || (sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND) 
  ){
    memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
    put32bits(&zHeader[sizeof(aJournalMagic)], 0xffffffff);
  }else{
    memset(zHeader, 0, sizeof(aJournalMagic)+4);
  }
................................................................................
  int rc;                          /* Return code */
  int nMaster;                     /* Length of string zMaster */
  i64 iHdrOff;                     /* Offset of header in journal file */
  i64 jrnlSize;                    /* Size of journal file on disk */
  u32 cksum = 0;                   /* Checksum of string zMaster */

  assert( pPager->setMaster==0 );


  if( !zMaster 
   || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
   || pPager->journalMode==PAGER_JOURNALMODE_OFF 
  ){
    return SQLITE_OK;
  }
  pPager->setMaster = 1;
................................................................................
   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster, nMaster)))
   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster+4, cksum)))
   || (0 != (rc = sqlite3OsWrite(pPager->jfd, aJournalMagic, 8, iHdrOff+4+nMaster+8)))
  ){
    return rc;
  }
  pPager->journalOff += (nMaster+20);
  pPager->needSync = !pPager->noSync;

  /* If the pager is in peristent-journal mode, then the physical 
  ** journal-file may extend past the end of the master-journal name
  ** and 8 bytes of magic data just written to the file. This is 
  ** dangerous because the code to rollback a hot-journal file
  ** will not be able to find the master-journal name to determine 
  ** whether or not the journal is hot. 
................................................................................
  ** fail, since no attempt to allocate dynamic memory will be made.
  */
  (void)sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &p);
  return p;
}

/*
** Unless the pager is in error-state, discard all in-memory pages. If
** the pager is in error-state, then this call is a no-op.
**
** TODO: Why can we not reset the pager while in error state?
*/
static void pager_reset(Pager *pPager){
  if( SQLITE_OK==pPager->errCode ){
    sqlite3BackupRestart(pPager->pBackup);
    sqlite3PcacheClear(pPager->pPCache);
    pPager->dbSizeValid = 0;
  }
}

/*
** Free all structures in the Pager.aSavepoint[] array and set both
** Pager.aSavepoint and Pager.nSavepoint to zero. Close the sub-journal
** if it is open and the pager is not in exclusive mode.
*/
................................................................................
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}

/*
** Return true if this pager uses a write-ahead log instead of the usual
** rollback journal. Otherwise false.
*/
#ifndef SQLITE_OMIT_WAL
static int pagerUseWal(Pager *pPager){
  return (pPager->pWal!=0);
}
#else
# define pagerUseWal(x) 0
# define pagerRollbackWal(x) 0
# define pagerWalFrames(v,w,x,y,z) 0
# define pagerOpenWalIfPresent(z) SQLITE_OK
# define pagerBeginReadTransaction(z) SQLITE_OK
#endif

/*
** Unlock the database file. This function is a no-op if the pager
** is in exclusive mode.
**
** If the pager is currently in error state, discard the contents of 
** the cache and reset the Pager structure internal state. If there is
** an open journal-file, then the next time a shared-lock is obtained
** on the pager file (by this or any other process), it will be
** treated as a hot-journal and rolled back.
*/
static void pager_unlock(Pager *pPager){
  if( !pPager->exclusiveMode ){
    int rc = SQLITE_OK;          /* Return code */





    int iDc = isOpen(pPager->fd)?sqlite3OsDeviceCharacteristics(pPager->fd):0;

    /* If the operating system support deletion of open files, then
    ** close the journal file when dropping the database lock.  Otherwise
    ** another connection with journal_mode=delete might delete the file
    ** out from under us.
    */
................................................................................
    assert( (PAGER_JOURNALMODE_PERSIST  & 5)==1 );
    if( 0==(iDc & SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN)
     || 1!=(pPager->journalMode & 5)
    ){
      sqlite3OsClose(pPager->jfd);
    }

    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
    releaseAllSavepoints(pPager);

    /* If the file is unlocked, somebody else might change it. The
    ** values stored in Pager.dbSize etc. might become invalid if
    ** this happens.  One can argue that this doesn't need to be cleared
    ** until the change-counter check fails in PagerSharedLock().
    ** Clearing the page size cache here is being conservative.
    */
    pPager->dbSizeValid = 0;

    if( pagerUseWal(pPager) ){
      sqlite3WalEndReadTransaction(pPager->pWal);
    }else{
      rc = osUnlock(pPager->fd, NO_LOCK);
    }
    if( rc ){
      pPager->errCode = rc;
    }
    IOTRACE(("UNLOCK %p\n", pPager))

    /* If Pager.errCode is set, the contents of the pager cache cannot be
    ** trusted. Now that the pager file is unlocked, the contents of the
    ** cache can be discarded and the error code safely cleared.
    */
    if( pPager->errCode ){
      if( rc==SQLITE_OK ){
        pPager->errCode = SQLITE_OK;
      }
      pager_reset(pPager);
    }

    pPager->changeCountDone = 0;
    pPager->state = PAGER_UNLOCK;
    pPager->dbModified = 0;
  }
}

/*
** This function should be called when an IOERR, CORRUPT or FULL error
** may have occurred. The first argument is a pointer to the pager 
** structure, the second the error-code about to be returned by a pager 
** API function. The value returned is a copy of the second argument 
** to this function. 
**
** If the second argument is SQLITE_IOERR, SQLITE_CORRUPT, or SQLITE_FULL
** the error becomes persistent. Until the persistent error is cleared,
** subsequent API calls on this Pager will immediately return the same 
** error code.
**
** A persistent error indicates that the contents of the pager-cache 
** cannot be trusted. This state can be cleared by completely discarding 
** the contents of the pager-cache. If a transaction was active when
** the persistent error occurred, then the rollback journal may need
** to be replayed to restore the contents of the database file (as if
** it were a hot-journal).
*/
static int pager_error(Pager *pPager, int rc){
................................................................................
  assert(
       pPager->errCode==SQLITE_FULL ||
       pPager->errCode==SQLITE_OK ||
       (pPager->errCode & 0xff)==SQLITE_IOERR
  );
  if( rc2==SQLITE_FULL || rc2==SQLITE_IOERR ){
    pPager->errCode = rc;

  }
  return rc;
}

/*
** Execute a rollback if a transaction is active and unlock the 
** database file. 
**
** If the pager has already entered the error state, do not attempt 
** the rollback at this time. Instead, pager_unlock() is called. The
** call to pager_unlock() will discard all in-memory pages, unlock
** the database file and clear the error state. If this means that
** there is a hot-journal left in the file-system, the next connection
** to obtain a shared lock on the pager (which may be this one) will
** roll it back.
**
** If the pager has not already entered the error state, but an IO or
** malloc error occurs during a rollback, then this will itself cause 
** the pager to enter the error state. Which will be cleared by the
** call to pager_unlock(), as described above.
*/
static void pagerUnlockAndRollback(Pager *pPager){
  if( pPager->errCode==SQLITE_OK && pPager->state>=PAGER_RESERVED ){
    sqlite3BeginBenignMalloc();
    sqlite3PagerRollback(pPager);
    sqlite3EndBenignMalloc();
  }
  pager_unlock(pPager);
}

/*
** This routine ends a transaction. A transaction is usually ended by 
** either a COMMIT or a ROLLBACK operation. This routine may be called 
** after rollback of a hot-journal, or if an error occurs while opening
** the journal file or writing the very first journal-header of a
** database transaction.
** 
** If the pager is in PAGER_SHARED or PAGER_UNLOCK state when this
** routine is called, it is a no-op (returns SQLITE_OK).

**
** Otherwise, any active savepoints are released.
**
** If the journal file is open, then it is "finalized". Once a journal 
** file has been finalized it is not possible to use it to roll back a 
** transaction. Nor will it be considered to be a hot-journal by this
** or any other database connection. Exactly how a journal is finalized
................................................................................
**     The journal file is closed and deleted using sqlite3OsDelete().
**
**     If the pager is running in exclusive mode, this method of finalizing
**     the journal file is never used. Instead, if the journalMode is
**     DELETE and the pager is in exclusive mode, the method described under
**     journalMode==PERSIST is used instead.
**
** After the journal is finalized, if running in non-exclusive mode, the
** pager moves to PAGER_SHARED state (and downgrades the lock on the
** database file accordingly).
**
** If the pager is running in exclusive mode and is in PAGER_SYNCED state,
** it moves to PAGER_EXCLUSIVE. No locks are downgraded when running in
** exclusive mode.
**
** SQLITE_OK is returned if no error occurs. If an error occurs during
** any of the IO operations to finalize the journal file or unlock the
** database then the IO error code is returned to the user. If the 
** operation to finalize the journal file fails, then the code still
** tries to unlock the database file if not in exclusive mode. If the
** unlock operation fails as well, then the first error code related
................................................................................
** to the first error encountered (the journal finalization one) is
** returned.
*/
static int pager_end_transaction(Pager *pPager, int hasMaster){
  int rc = SQLITE_OK;      /* Error code from journal finalization operation */
  int rc2 = SQLITE_OK;     /* Error code from db file unlock operation */

  if( pPager->state<PAGER_RESERVED ){















    return SQLITE_OK;
  }
  releaseAllSavepoints(pPager);


  assert( isOpen(pPager->jfd) || pPager->pInJournal==0 );
  if( isOpen(pPager->jfd) ){
    assert( !pagerUseWal(pPager) );

    /* Finalize the journal file. */
    if( sqlite3IsMemJournal(pPager->jfd) ){
      assert( pPager->journalMode==PAGER_JOURNALMODE_MEMORY );
................................................................................
    }else if( pPager->journalMode==PAGER_JOURNALMODE_TRUNCATE ){
      if( pPager->journalOff==0 ){
        rc = SQLITE_OK;
      }else{
        rc = sqlite3OsTruncate(pPager->jfd, 0);
      }
      pPager->journalOff = 0;
      pPager->journalStarted = 0;
    }else if( pPager->journalMode==PAGER_JOURNALMODE_PERSIST
      || (pPager->exclusiveMode && pPager->journalMode!=PAGER_JOURNALMODE_WAL)
    ){
      rc = zeroJournalHdr(pPager, hasMaster);
      pager_error(pPager, rc);
      pPager->journalOff = 0;
      pPager->journalStarted = 0;
    }else{
      /* This branch may be executed with Pager.journalMode==MEMORY if
      ** a hot-journal was just rolled back. In this case the journal
      ** file should be closed and deleted. If this connection writes to
      ** the database file, it will do so using an in-memory journal. 
      */
      assert( pPager->journalMode==PAGER_JOURNALMODE_DELETE 
................................................................................
    sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
#endif
  }
  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  pPager->nRec = 0;
  sqlite3PcacheCleanAll(pPager->pPCache);


  if( pagerUseWal(pPager) ){
    rc2 = sqlite3WalEndWriteTransaction(pPager->pWal);
    assert( rc2==SQLITE_OK );
    pPager->state = PAGER_SHARED;

    /* If the connection was in locking_mode=exclusive mode but is no longer,
    ** drop the EXCLUSIVE lock held on the database file.
    */
    if( !pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, 0) ){
      rc2 = osUnlock(pPager->fd, SHARED_LOCK);


    }
  }else if( !pPager->exclusiveMode ){


    rc2 = osUnlock(pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    pPager->changeCountDone = 0;
  }else if( pPager->state==PAGER_SYNCED ){
    pPager->state = PAGER_EXCLUSIVE;
  }

  pPager->setMaster = 0;
  pPager->needSync = 0;
  pPager->dbModified = 0;





  /* TODO: Is this optimal? Why is the db size invalidated here 
  ** when the database file is not unlocked? */
  pPager->dbOrigSize = 0;

  sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);
  if( !MEMDB ){
    pPager->dbSizeValid = 0;




















  }

  return (rc==SQLITE_OK?rc2:rc);

}

/*
** Parameter aData must point to a buffer of pPager->pageSize bytes
** of data. Compute and return a checksum based ont the contents of the 
** page of data and the current value of pPager->cksumInit.
**
** This is not a real checksum. It is really just the sum of the 
................................................................................

/*
** Read a single page from either the journal file (if isMainJrnl==1) or
** from the sub-journal (if isMainJrnl==0) and playback that page.
** The page begins at offset *pOffset into the file. The *pOffset
** value is increased to the start of the next page in the journal.
**
** The isMainJrnl flag is true if this is the main rollback journal and
** false for the statement journal.  The main rollback journal uses
** checksums - the statement journal does not.
**
** If the page number of the page record read from the (sub-)journal file
** is greater than the current value of Pager.dbSize, then playback is
** skipped and SQLITE_OK is returned.
**
** If pDone is not NULL, then it is a record of pages that have already
** been played back.  If the page at *pOffset has already been played back
................................................................................
  assert( (isSavepnt&~1)==0 );       /* isSavepnt is 0 or 1 */
  assert( isMainJrnl || pDone );     /* pDone always used on sub-journals */
  assert( isSavepnt || pDone==0 );   /* pDone never used on non-savepoint */

  aData = pPager->pTmpSpace;
  assert( aData );         /* Temp storage must have already been allocated */
  assert( pagerUseWal(pPager)==0 || (!isMainJrnl && isSavepnt) );












  /* Read the page number and page data from the journal or sub-journal
  ** file. Return an error code to the caller if an IO error occurs.
  */
  jfd = isMainJrnl ? pPager->jfd : pPager->sjfd;
  rc = read32bits(jfd, *pOffset, &pgno);
  if( rc!=SQLITE_OK ) return rc;
................................................................................

  /* If this page has already been played by before during the current
  ** rollback, then don't bother to play it back again.
  */
  if( pDone && (rc = sqlite3BitvecSet(pDone, pgno))!=SQLITE_OK ){
    return rc;
  }
  assert( pPager->state==PAGER_RESERVED || pPager->state>=PAGER_EXCLUSIVE );

  /* When playing back page 1, restore the nReserve setting
  */
  if( pgno==1 && pPager->nReserve!=((u8*)aData)[20] ){
    pPager->nReserve = ((u8*)aData)[20];
    pagerReportSize(pPager);
  }

  /* If the pager is in RESERVED state, then there must be a copy of this
  ** page in the pager cache. In this case just update the pager cache,
  ** not the database file. The page is left marked dirty in this case.
  **
  ** An exception to the above rule: If the database is in no-sync mode
  ** and a page is moved during an incremental vacuum then the page may
  ** not be in the pager cache. Later: if a malloc() or IO error occurs
  ** during a Movepage() call, then the page may not be in the cache
  ** either. So the condition described in the above paragraph is not
  ** assert()able.
  **
  ** If in EXCLUSIVE state, then we update the pager cache if it exists
  ** and the main file. The page is then marked not dirty.



  **
  ** Ticket #1171:  The statement journal might contain page content that is
  ** different from the page content at the start of the transaction.
  ** This occurs when a page is changed prior to the start of a statement
  ** then changed again within the statement.  When rolling back such a
  ** statement we must not write to the original database unless we know
  ** for certain that original page contents are synced into the main rollback
................................................................................
  */
  if( pagerUseWal(pPager) ){
    pPg = 0;
  }else{
    pPg = pager_lookup(pPager, pgno);
  }
  assert( pPg || !MEMDB );

  PAGERTRACE(("PLAYBACK %d page %d hash(%08x) %s\n",
           PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, (u8*)aData),
           (isMainJrnl?"main-journal":"sub-journal")
  ));
  if( isMainJrnl ){
    isSynced = pPager->noSync || (*pOffset <= pPager->journalHdr);
  }else{
    isSynced = (pPg==0 || 0==(pPg->flags & PGHDR_NEED_SYNC));
  }
  if( (pPager->state>=PAGER_EXCLUSIVE)
   && isOpen(pPager->fd)
   && isSynced
  ){
    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
    testcase( !isSavepnt && pPg!=0 && (pPg->flags&PGHDR_NEED_SYNC)!=0 );
    assert( !pagerUseWal(pPager) );
    rc = sqlite3OsWrite(pPager->fd, (u8*)aData, pPager->pageSize, ofst);
................................................................................


/*
** This function is used to change the actual size of the database 
** file in the file-system. This only happens when committing a transaction,
** or rolling back a transaction (including rolling back a hot-journal).
**
** If the main database file is not open, or an exclusive lock is not
** held, this function is a no-op. Otherwise, the size of the file is
** changed to nPage pages (nPage*pPager->pageSize bytes). If the file
** on disk is currently larger than nPage pages, then use the VFS
** xTruncate() method to truncate it.
**
** Or, it might might be the case that the file on disk is smaller than 
** nPage pages. Some operating system implementations can get confused if 
** you try to truncate a file to some size that is larger than it 
** currently is, so detect this case and write a single zero byte to 
** the end of the new file instead.
**
** If successful, return SQLITE_OK. If an IO error occurs while modifying
** the database file, return the error code to the caller.
*/
static int pager_truncate(Pager *pPager, Pgno nPage){
  int rc = SQLITE_OK;



  if( pPager->state>=PAGER_EXCLUSIVE && isOpen(pPager->fd) ){


    i64 currentSize, newSize;

    /* TODO: Is it safe to use Pager.dbFileSize here? */
    rc = sqlite3OsFileSize(pPager->fd, &currentSize);
    newSize = pPager->pageSize*(i64)nPage;
    if( rc==SQLITE_OK && currentSize!=newSize ){
      if( currentSize>newSize ){
        rc = sqlite3OsTruncate(pPager->fd, newSize);
      }else{
................................................................................
  u32 nRec;                /* Number of Records in the journal */
  u32 u;                   /* Unsigned loop counter */
  Pgno mxPg = 0;           /* Size of the original file in pages */
  int rc;                  /* Result code of a subroutine */
  int res = 1;             /* Value returned by sqlite3OsAccess() */
  char *zMaster = 0;       /* Name of master journal file if any */
  int needPagerReset;      /* True to reset page prior to first page rollback */





  /* Figure out how many records are in the journal.  Abort early if
  ** the journal is empty.
  */
  assert( isOpen(pPager->jfd) );
  rc = sqlite3OsFileSize(pPager->jfd, &szJ);
  if( rc!=SQLITE_OK || szJ==0 ){
    goto end_playback;
  }

  /* Read the master journal name from the journal, if it is present.
  ** If a master journal file name is specified, but the file is not
................................................................................
  pPager->changeCountDone = pPager->tempFile;

  if( rc==SQLITE_OK ){
    zMaster = pPager->pTmpSpace;
    rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
    testcase( rc!=SQLITE_OK );
  }
  if( rc==SQLITE_OK && pPager->noSync==0 && pPager->state>=PAGER_EXCLUSIVE ){
    rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
  }
  if( rc==SQLITE_OK && pPager->noSync==0 && pPager->state>=PAGER_EXCLUSIVE ){

    rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
  }
  if( rc==SQLITE_OK ){
    rc = pager_end_transaction(pPager, zMaster[0]!='\0');
    testcase( rc!=SQLITE_OK );
  }
  if( rc==SQLITE_OK && zMaster[0] && res ){
................................................................................
static int readDbPage(PgHdr *pPg){
  Pager *pPager = pPg->pPager; /* Pager object associated with page pPg */
  Pgno pgno = pPg->pgno;       /* Page number to read */
  int rc = SQLITE_OK;          /* Return code */
  int isInWal = 0;             /* True if page is in log file */
  int pgsz = pPager->pageSize; /* Number of bytes to read */

  assert( pPager->state>=PAGER_SHARED && !MEMDB );
  assert( isOpen(pPager->fd) );

  if( NEVER(!isOpen(pPager->fd)) ){
    assert( pPager->tempFile );
    memset(pPg->pData, 0, pPager->pageSize);
    return SQLITE_OK;
  }
................................................................................
** other writers or checkpointers.
*/
static int pagerBeginReadTransaction(Pager *pPager){
  int rc;                         /* Return code */
  int changed = 0;                /* True if cache must be reset */

  assert( pagerUseWal(pPager) );


  /* sqlite3WalEndReadTransaction() was not called for the previous
  ** transaction in locking_mode=EXCLUSIVE.  So call it now.  If we
  ** are in locking_mode=NORMAL and EndRead() was previously called,
  ** the duplicate call is harmless.
  */
  sqlite3WalEndReadTransaction(pPager->pWal);

  rc = sqlite3WalBeginReadTransaction(pPager->pWal, &changed);
  if( rc==SQLITE_OK ){
    int dummy;
    if( changed ){
      pager_reset(pPager);
      assert( pPager->errCode || pPager->dbSizeValid==0 );
    }
    rc = sqlite3PagerPagecount(pPager, &dummy);
  }
  pPager->state = PAGER_SHARED;





































  return rc;
}




















/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists if the database is not empy, or verify that the *-wal file does
** not exist (by deleting it) if the database file is empty.
**
** If the database is not empty and the *-wal file exists, open the pager
** in WAL mode.  If the database is empty or if no *-wal file exists and
** if no error occurs, make sure Pager.journalMode is not set to
** PAGER_JOURNALMODE_WAL.
**
** Return SQLITE_OK or an error code.
**
** If the WAL file is opened, also open a snapshot (read transaction).
**
** The caller must hold a SHARED lock on the database file to call this
** function. Because an EXCLUSIVE lock on the db file is required to delete 
** a WAL on a none-empty database, this ensures there is no race condition 
** between the xAccess() below and an xDelete() being executed by some 
** other connection.
*/
static int pagerOpenWalIfPresent(Pager *pPager){
  int rc = SQLITE_OK;



  if( !pPager->tempFile ){
    int isWal;                    /* True if WAL file exists */
    int nPage;                    /* Size of the database file */
    assert( pPager->state>=SHARED_LOCK );

    rc = sqlite3PagerPagecount(pPager, &nPage);
    if( rc ) return rc;
    if( nPage==0 ){
      rc = sqlite3OsDelete(pPager->pVfs, pPager->zWal, 0);
      isWal = 0;
    }else{
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &isWal
      );
    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        pager_reset(pPager);
        rc = sqlite3PagerOpenWal(pPager, 0);
        if( rc==SQLITE_OK ){
          rc = pagerBeginReadTransaction(pPager);
        }
      }else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
        pPager->journalMode = PAGER_JOURNALMODE_DELETE;
      }
    }
  }
  return rc;
}
................................................................................
*/
static int pagerPlaybackSavepoint(Pager *pPager, PagerSavepoint *pSavepoint){
  i64 szJ;                 /* Effective size of the main journal */
  i64 iHdrOff;             /* End of first segment of main-journal records */
  int rc = SQLITE_OK;      /* Return code */
  Bitvec *pDone = 0;       /* Bitvec to ensure pages played back only once */

  assert( pPager->state>=PAGER_SHARED );


  /* Allocate a bitvec to use to store the set of pages rolled back */
  if( pSavepoint ){
    pDone = sqlite3BitvecCreate(pSavepoint->nOrig);
    if( !pDone ){
      return SQLITE_NOMEM;
    }
................................................................................
** and FULL=3.
*/
#ifndef SQLITE_OMIT_PAGER_PRAGMAS
void sqlite3PagerSetSafetyLevel(Pager *pPager, int level, int bFullFsync){
  pPager->noSync =  (level==1 || pPager->tempFile) ?1:0;
  pPager->fullSync = (level==3 && !pPager->tempFile) ?1:0;
  pPager->sync_flags = (bFullFsync?SQLITE_SYNC_FULL:SQLITE_SYNC_NORMAL);
  if( pPager->noSync ) pPager->needSync = 0;
}
#endif

/*
** The following global variable is incremented whenever the library
** attempts to open a temporary file.  This information is used for
** testing and analysis only.  
................................................................................
** conditions above is not true, the pager was in error state when this
** function was called, or because the memory allocation attempt failed, 
** then *pPageSize is set to the old, retained page size before returning.
*/
int sqlite3PagerSetPagesize(Pager *pPager, u16 *pPageSize, int nReserve){
  int rc = pPager->errCode;







  if( rc==SQLITE_OK ){
    u16 pageSize = *pPageSize;
    assert( pageSize==0 || (pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE) );
    if( (pPager->memDb==0 || pPager->dbSize==0)
     && sqlite3PcacheRefCount(pPager->pPCache)==0 
     && pageSize && pageSize!=pPager->pageSize 
    ){






      char *pNew = (char *)sqlite3PageMalloc(pageSize);
      if( !pNew ){
        rc = SQLITE_NOMEM;
      }else{
        pager_reset(pPager);

        pPager->pageSize = pageSize;
        sqlite3PageFree(pPager->pTmpSpace);
        pPager->pTmpSpace = pNew;
        sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
      }
    }
    *pPageSize = (u16)pPager->pageSize;
................................................................................
** Attempt to set the maximum database page count if mxPage is positive. 
** Make no changes if mxPage is zero or negative.  And never reduce the
** maximum page count below the current size of the database.
**
** Regardless of mxPage, return the current maximum page count.
*/
int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){
  int nPage;
  if( mxPage>0 ){
    pPager->mxPgno = mxPage;
  }
  if( pPager->state!=PAGER_UNLOCK ){
    sqlite3PagerPagecount(pPager, &nPage);
    assert( (int)pPager->mxPgno>=nPage );
  }
  return pPager->mxPgno;
}

/*
** The following set of routines are used to disable the simulated
** I/O error mechanism.  These routines are used to avoid simulated
................................................................................
      rc = SQLITE_OK;
    }
  }
  return rc;
}

/*

** Return the total number of pages in the database file associated 
** with pPager. Normally, this is calculated as (<db file size>/<page-size>).

** However, if the file is between 1 and <page-size> bytes in size, then 
** this is considered a 1 page file.
**
** If the pager is in error state when this function is called, then the
** error state error code is returned and *pnPage left unchanged. Or,
** if the file system has to be queried for the size of the file and
** the query attempt returns an IO error, the IO error code is returned
** and *pnPage is left unchanged.
**
** Otherwise, if everything is successful, then SQLITE_OK is returned
** and *pnPage is set to the number of pages in the database.
*/
int sqlite3PagerPagecount(Pager *pPager, int *pnPage){
  Pgno nPage = 0;           /* Value to return via *pnPage */

  /* Determine the number of pages in the file. Store this in nPage. */
  if( pPager->dbSizeValid ){
    nPage = pPager->dbSize;
  }else{
    int rc;                 /* Error returned by OsFileSize() */
    i64 n = 0;              /* File size in bytes returned by OsFileSize() */

    if( pagerUseWal(pPager) && pPager->state!=PAGER_UNLOCK ){
      sqlite3WalDbsize(pPager->pWal, &nPage);
    }

    if( nPage==0 ){
      assert( isOpen(pPager->fd) || pPager->tempFile );
      if( isOpen(pPager->fd) ){
        if( SQLITE_OK!=(rc = sqlite3OsFileSize(pPager->fd, &n)) ){
          pager_error(pPager, rc);
          return rc;
        }
      }
      if( n>0 && n<pPager->pageSize ){
        nPage = 1;
      }else{
        nPage = (Pgno)(n / pPager->pageSize);
      }
    }
    if( pPager->state!=PAGER_UNLOCK ){


      pPager->dbSize = nPage;
      pPager->dbFileSize = nPage;
      pPager->dbSizeValid = 1;
    }
  }

  /* If the current number of pages in the file is greater than the 
  ** configured maximum pager number, increase the allowed limit so
  ** that the file can be read.
  */
  if( nPage>pPager->mxPgno ){
    pPager->mxPgno = (Pgno)nPage;
  }

  /* Set the output variable and return SQLITE_OK */
  *pnPage = nPage;
  return SQLITE_OK;
}


/*
** Try to obtain a lock of type locktype on the database file. If
** a similar or greater lock is already held, this function is a no-op
................................................................................
** Return SQLITE_OK on success and an error code if we cannot obtain
** the lock. If the lock is obtained successfully, set the Pager.state 
** variable to locktype before returning.
*/
static int pager_wait_on_lock(Pager *pPager, int locktype){
  int rc;                              /* Return code */

  /* The OS lock values must be the same as the Pager lock values */
  assert( PAGER_SHARED==SHARED_LOCK );
  assert( PAGER_RESERVED==RESERVED_LOCK );
  assert( PAGER_EXCLUSIVE==EXCLUSIVE_LOCK );

  /* If the file is currently unlocked then the size must be unknown. It
  ** must not have been modified at this point.
  */
  assert( pPager->state>=PAGER_SHARED || pPager->dbSizeValid==0 );
  assert( pPager->state>=PAGER_SHARED || pPager->dbModified==0 );

  /* Check that this is either a no-op (because the requested lock is 
  ** already held, or one of the transistions that the busy-handler
  ** may be invoked during, according to the comment above
  ** sqlite3PagerSetBusyhandler().
  */
  assert( (pPager->state>=locktype)
       || (pPager->state==PAGER_UNLOCK && locktype==PAGER_SHARED)
       || (pPager->state==PAGER_RESERVED && locktype==PAGER_EXCLUSIVE)
  );

  if( pPager->state>=locktype ){
    rc = SQLITE_OK;
  }else{
    do {
      rc = sqlite3OsLock(pPager->fd, locktype);

    }while( rc==SQLITE_BUSY && pPager->xBusyHandler(pPager->pBusyHandlerArg) );
    if( rc==SQLITE_OK ){
      pPager->state = (u8)locktype;
      IOTRACE(("LOCK %p %d\n", pPager, locktype))
    }
  }
  return rc;
}

/*
** Function assertTruncateConstraint(pPager) checks that one of the 
** following is true for all dirty pages currently in the page-cache:
**
................................................................................
/*
** Truncate the in-memory database file image to nPage pages. This 
** function does not actually modify the database file on disk. It 
** just sets the internal state of the pager object so that the 
** truncation will be done when the current transaction is committed.
*/
void sqlite3PagerTruncateImage(Pager *pPager, Pgno nPage){
  assert( pPager->dbSizeValid );
  assert( pPager->dbSize>=nPage );
  assert( pPager->state>=PAGER_RESERVED );
  pPager->dbSize = nPage;
  assertTruncateConstraint(pPager);
}


/*
** This function is called before attempting a hot-journal rollback. It
................................................................................
** to the caller.
*/
int sqlite3PagerClose(Pager *pPager){
  u8 *pTmp = (u8 *)pPager->pTmpSpace;

  disable_simulated_io_errors();
  sqlite3BeginBenignMalloc();
  pPager->errCode = 0;
  pPager->exclusiveMode = 0;
#ifndef SQLITE_OMIT_WAL
  sqlite3WalClose(pPager->pWal,
    (pPager->noSync ? 0 : pPager->sync_flags), 
    pPager->pageSize, pTmp
  );
  pPager->pWal = 0;
#endif
  pager_reset(pPager);
  if( MEMDB ){
    pager_unlock(pPager);
  }else{
    /* Set Pager.journalHdr to -1 for the benefit of the pager_playback() 
    ** call which may be made from within pagerUnlockAndRollback(). If it
    ** is not -1, then the unsynced portion of an open journal file may
    ** be played back into the database. If a power failure occurs while
    ** this is happening, the database may become corrupt.






    */
    if( isOpen(pPager->jfd) ){
      pPager->errCode = pagerSyncHotJournal(pPager);
    }
    pagerUnlockAndRollback(pPager);
  }
  sqlite3EndBenignMalloc();
  enable_simulated_io_errors();
  PAGERTRACE(("CLOSE %d\n", PAGERID(pPager)));
  IOTRACE(("CLOSE %p\n", pPager))
................................................................................
}

/*
** Sync the journal. In other words, make sure all the pages that have
** been written to the journal have actually reached the surface of the
** disk and can be restored in the event of a hot-journal rollback.
**
** If the Pager.needSync flag is not set, then this function is a
** no-op. Otherwise, the actions required depend on the journal-mode
** and the device characteristics of the the file-system, as follows:
**
**   * If the journal file is an in-memory journal file, no action need
**     be taken.
**
**   * Otherwise, if the device does not support the SAFE_APPEND property,
**     then the nRec field of the most recently written journal header
**     is updated to contain the number of journal records that have
................................................................................
**     if( NOT SAFE_APPEND ){
**       if( <full-sync mode> ) xSync(<journal file>);
**       <update nRec field>
**     } 
**     if( NOT SEQUENTIAL ) xSync(<journal file>);
**   }
**
** The Pager.needSync flag is never be set for temporary files, or any
** file operating in no-sync mode (Pager.noSync set to non-zero).
**
** If successful, this routine clears the PGHDR_NEED_SYNC flag of every 
** page currently held in memory before returning SQLITE_OK. If an IO
** error is encountered, then the IO error code is returned to the caller.
*/
static int syncJournal(Pager *pPager){











  if( pPager->needSync ){
    assert( !pPager->tempFile );
    if( pPager->journalMode!=PAGER_JOURNALMODE_MEMORY ){
      int rc;                              /* Return code */
      const int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
      assert( isOpen(pPager->jfd) );

      if( 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
        /* This block deals with an obscure problem. If the last connection
        ** that wrote to this database was operating in persistent-journal
        ** mode, then the journal file may at this point actually be larger
................................................................................
        PAGERTRACE(("SYNC journal of %d\n", PAGERID(pPager)));
        IOTRACE(("JSYNC %p\n", pPager))
        rc = sqlite3OsSync(pPager->jfd, pPager->sync_flags| 
          (pPager->sync_flags==SQLITE_SYNC_FULL?SQLITE_SYNC_DATAONLY:0)
        );
        if( rc!=SQLITE_OK ) return rc;
      }
    }






    /* The journal file was just successfully synced. Set Pager.needSync 
    ** to zero and clear the PGHDR_NEED_SYNC flag on all pagess.
    */
    pPager->needSync = 0;
    pPager->journalStarted = 1;

    pPager->journalHdr = pPager->journalOff;
    sqlite3PcacheClearSyncFlags(pPager->pPCache);
  }









  return SQLITE_OK;
}

/*
** The argument is the first in a linked list of dirty pages connected
** by the PgHdr.pDirty pointer. This function writes each one of the
** in-memory pages in the list to the database file. The argument may
................................................................................
** the database file.
**
** If everything is successful, SQLITE_OK is returned. If an IO error 
** occurs, an IO error code is returned. Or, if the EXCLUSIVE lock cannot
** be obtained, SQLITE_BUSY is returned.
*/
static int pager_write_pagelist(Pager *pPager, PgHdr *pList){
  int rc;                              /* Return code */

  /* At this point there may be either a RESERVED or EXCLUSIVE lock on the
  ** database file. If there is already an EXCLUSIVE lock, the following
  ** call is a no-op.
  **
  ** Moving the lock from RESERVED to EXCLUSIVE actually involves going
  ** through an intermediate state PENDING.   A PENDING lock prevents new
  ** readers from attaching to the database but is unsufficient for us to
  ** write.  The idea of a PENDING lock is to prevent new readers from
  ** coming in while we wait for existing readers to clear.
  **
  ** While the pager is in the RESERVED state, the original database file
  ** is unchanged and we can rollback without having to playback the
  ** journal into the original database file.  Once we transition to
  ** EXCLUSIVE, it means the database file has been changed and any rollback
  ** will require a journal playback.
  */
  assert( !pagerUseWal(pPager) );

  assert( pPager->state>=PAGER_RESERVED );
  rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);

  /* If the file is a temp-file has not yet been opened, open it now. It
  ** is not possible for rc to be other than SQLITE_OK if this branch
  ** is taken, as pager_wait_on_lock() is a no-op for temp-files.
  */
  if( !isOpen(pPager->fd) ){
    assert( pPager->tempFile && rc==SQLITE_OK );
................................................................................
    rc = pagerOpentemp(pPager, pPager->fd, pPager->vfsFlags);
  }

  /* Before the first write, give the VFS a hint of what the final
  ** file size will be.
  */
  assert( rc!=SQLITE_OK || isOpen(pPager->fd) );
  if( rc==SQLITE_OK && pPager->dbSize>(pPager->dbOrigSize+1) ){
    sqlite3_int64 szFile = pPager->pageSize * (sqlite3_int64)pPager->dbSize;
    sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_SIZE_HINT, &szFile);

  }

  while( rc==SQLITE_OK && pList ){
    Pgno pgno = pList->pgno;

    /* If there are dirty pages in the page cache with page numbers greater
    ** than Pager.dbSize, this means sqlite3PagerTruncateImage() was called to
................................................................................
    **
    ** Also, do not write out any page that has the PGHDR_DONT_WRITE flag
    ** set (set by sqlite3PagerDontWrite()).
    */
    if( pgno<=pPager->dbSize && 0==(pList->flags&PGHDR_DONT_WRITE) ){
      i64 offset = (pgno-1)*(i64)pPager->pageSize;   /* Offset to write */
      char *pData;                                   /* Data to write */    



      /* Encode the database */
      CODEC2(pPager, pList->pData, pgno, 6, return SQLITE_NOMEM, pData);

      /* Write out the page data. */
      rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize, offset);

................................................................................
    }
    if( rc==SQLITE_OK ){
      rc = pagerWalFrames(pPager, pPg, 0, 0, 0);
    }
  }else{
  
    /* Sync the journal file if required. */
    if( pPg->flags&PGHDR_NEED_SYNC ){
      assert( !pPager->noSync );
      rc = syncJournal(pPager);
      if( rc==SQLITE_OK && 
        !(pPager->journalMode==PAGER_JOURNALMODE_MEMORY) &&
        !(sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND)
      ){
        pPager->nRec = 0;
        rc = writeJournalHdr(pPager);
      }

    }
  
    /* If the page number of this page is larger than the current size of
    ** the database image, it may need to be written to the sub-journal.
    ** This is because the call to pager_write_pagelist() below will not
    ** actually write data to the file in this case.
    **
................................................................................
        rc==SQLITE_OK && pPg->pgno>pPager->dbSize && subjRequiresPage(pPg)
    ) ){
      rc = subjournalPage(pPg);
    }
  
    /* Write the contents of the page out to the database file. */
    if( rc==SQLITE_OK ){

      rc = pager_write_pagelist(pPager, pPg);
    }
  }

  /* Mark the page as clean. */
  if( rc==SQLITE_OK ){
    PAGERTRACE(("STRESS %d page %d\n", PAGERID(pPager), pPg->pgno));
................................................................................
    ** opening the file until the first call to OsWrite().
    **
    ** This branch is also run for an in-memory database. An in-memory
    ** database is the same as a temp-file that is never written out to
    ** disk and uses an in-memory rollback journal.
    */ 
    tempFile = 1;
    pPager->state = PAGER_EXCLUSIVE;

    readOnly = (vfsFlags&SQLITE_OPEN_READONLY);
  }

  /* The following call to PagerSetPagesize() serves to set the value of 
  ** Pager.pageSize and to allocate the Pager.pTmpSpace buffer.
  */
  if( rc==SQLITE_OK ){
................................................................................
  IOTRACE(("OPEN %p %s\n", pPager, pPager->zFilename))

  pPager->useJournal = (u8)useJournal;
  pPager->noReadlock = (noReadlock && readOnly) ?1:0;
  /* pPager->stmtOpen = 0; */
  /* pPager->stmtInUse = 0; */
  /* pPager->nRef = 0; */
  pPager->dbSizeValid = (u8)memDb;
  /* pPager->stmtSize = 0; */
  /* pPager->stmtJSize = 0; */
  /* pPager->nPage = 0; */
  pPager->mxPgno = SQLITE_MAX_PAGE_COUNT;
  /* pPager->state = PAGER_UNLOCK; */

  assert( pPager->state == (tempFile ? PAGER_EXCLUSIVE : PAGER_UNLOCK) );

  /* pPager->errMask = 0; */
  pPager->tempFile = (u8)tempFile;
  assert( tempFile==PAGER_LOCKINGMODE_NORMAL 
          || tempFile==PAGER_LOCKINGMODE_EXCLUSIVE );
  assert( PAGER_LOCKINGMODE_EXCLUSIVE==1 );
  pPager->exclusiveMode = (u8)tempFile; 
  pPager->changeCountDone = pPager->tempFile;
  pPager->memDb = (u8)memDb;
  pPager->readOnly = (u8)readOnly;
  /* pPager->needSync = 0; */
  assert( useJournal || pPager->tempFile );
  pPager->noSync = pPager->tempFile;
  pPager->fullSync = pPager->noSync ?0:1;
  pPager->sync_flags = SQLITE_SYNC_NORMAL;
  /* pPager->pFirst = 0; */
  /* pPager->pFirstSynced = 0; */
  /* pPager->pLast = 0; */
................................................................................
*/
static int hasHotJournal(Pager *pPager, int *pExists){
  sqlite3_vfs * const pVfs = pPager->pVfs;
  int rc = SQLITE_OK;           /* Return code */
  int exists = 1;               /* True if a journal file is present */
  int jrnlOpen = !!isOpen(pPager->jfd);

  assert( pPager!=0 );
  assert( pPager->useJournal );
  assert( isOpen(pPager->fd) );
  assert( pPager->state <= PAGER_SHARED );

  assert( jrnlOpen==0 || ( sqlite3OsDeviceCharacteristics(pPager->jfd) &
    SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN
  ));

  *pExists = 0;
  if( !jrnlOpen ){
    rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
  }
  if( rc==SQLITE_OK && exists ){
    int locked;                 /* True if some process holds a RESERVED lock */

    /* Race condition here:  Another process might have been holding the
    ** the RESERVED lock and have a journal open at the sqlite3OsAccess() 
    ** call above, but then delete the journal and drop the lock before
    ** we get to the following sqlite3OsCheckReservedLock() call.  If that
    ** is the case, this routine might think there is a hot journal when
    ** in fact there is none.  This results in a false-positive which will
    ** be dealt with by the playback routine.  Ticket #3883.
    */
    rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
    if( rc==SQLITE_OK && !locked ){
      int nPage;

      /* Check the size of the database file. If it consists of 0 pages,
      ** then delete the journal file. See the header comment above for 
      ** the reasoning here.  Delete the obsolete journal file under
      ** a RESERVED lock to avoid race conditions and to avoid violating
      ** [H33020].
      */
      rc = sqlite3PagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK ){
        if( nPage==0 ){
          sqlite3BeginBenignMalloc();
          if( sqlite3OsLock(pPager->fd, RESERVED_LOCK)==SQLITE_OK ){
            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
            sqlite3OsUnlock(pPager->fd, SHARED_LOCK);
          }
          sqlite3EndBenignMalloc();
        }else{
          /* The journal file exists and no other connection has a reserved
          ** or greater lock on the database file. Now check that there is
          ** at least one non-zero bytes at the start of the journal file.
          ** If there is, then we consider this journal to be hot. If not, 
................................................................................
**
** Otherwise, if everything is successful, SQLITE_OK is returned. If an
** IO error occurs while locking the database, checking for a hot-journal
** file or rolling back a journal file, the IO error code is returned.
*/
int sqlite3PagerSharedLock(Pager *pPager){
  int rc = SQLITE_OK;                /* Return code */
  int isErrorReset = 0;              /* True if recovering from error state */

  /* This routine is only called from b-tree and only when there are no
  ** outstanding pages */



  assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );


  if( NEVER(MEMDB && pPager->errCode) ){ return pPager->errCode; }

  /* If this database is in an error-state, now is a chance to clear
  ** the error. Discard the contents of the pager-cache and rollback
  ** any hot journal in the file-system.
  */
  if( pPager->errCode ){
    if( isOpen(pPager->jfd) || pPager->zJournal ){
      isErrorReset = 1;
    }

    pPager->errCode = SQLITE_OK;
    pager_reset(pPager);
  }

  if( pagerUseWal(pPager) ){
    rc = pagerBeginReadTransaction(pPager);
  }else if( pPager->state==PAGER_UNLOCK || isErrorReset ){
    sqlite3_vfs * const pVfs = pPager->pVfs;
    int isHotJournal = 0;
    assert( !MEMDB );
    assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
    if( pPager->noReadlock ){
      assert( pPager->readOnly );
      pPager->state = PAGER_SHARED;
    }else{
      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
      if( rc!=SQLITE_OK ){
        assert( pPager->state==PAGER_UNLOCK );
        return pager_error(pPager, rc);


      }
    }
    assert( pPager->state>=SHARED_LOCK );

    /* If a journal file exists, and there is no RESERVED lock on the
    ** database file, then it either needs to be played back or deleted.
    */
    if( !isErrorReset ){
      assert( pPager->state <= PAGER_SHARED );
      rc = hasHotJournal(pPager, &isHotJournal);

      if( rc!=SQLITE_OK ){
        goto failed;
      }
    }
    if( isErrorReset || isHotJournal ){
      /* Get an EXCLUSIVE lock on the database file. At this point it is
      ** important that a RESERVED lock is not obtained on the way to the
      ** EXCLUSIVE lock. If it were, another process might open the
      ** database file, detect the RESERVED lock, and conclude that the
      ** database is safe to read while this process is still rolling the 
      ** hot-journal back.
      ** 
      ** Because the intermediate RESERVED lock is not requested, any
      ** other process attempting to access the database file will get to 
      ** this point in the code and fail to obtain its own EXCLUSIVE lock 
      ** on the database file.



      */
      if( pPager->state<EXCLUSIVE_LOCK ){
        rc = sqlite3OsLock(pPager->fd, EXCLUSIVE_LOCK);
        if( rc!=SQLITE_OK ){
          rc = pager_error(pPager, rc);
          goto failed;
        }
        pPager->state = PAGER_EXCLUSIVE;
      }
 

      /* Open the journal for read/write access. This is because in 
      ** exclusive-access mode the file descriptor will be kept open and
      ** possibly used for a transaction later on. On some systems, the
      ** OsTruncate() call used in exclusive-access mode also requires
      ** a read/write file handle.






      */
      if( !isOpen(pPager->jfd) ){
        int res;


        rc = sqlite3OsAccess(pVfs,pPager->zJournal,SQLITE_ACCESS_EXISTS,&res);

        if( rc==SQLITE_OK ){
          if( res ){
            int fout = 0;
            int f = SQLITE_OPEN_READWRITE|SQLITE_OPEN_MAIN_JOURNAL;
            assert( !pPager->tempFile );
            rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &fout);
            assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
            if( rc==SQLITE_OK && fout&SQLITE_OPEN_READONLY ){
              rc = SQLITE_CANTOPEN_BKPT;
              sqlite3OsClose(pPager->jfd);
            }
          }else{
            /* If the journal does not exist, it usually means that some 
            ** other connection managed to get in and roll it back before 
            ** this connection obtained the exclusive lock above. Or, it 
            ** may mean that the pager was in the error-state when this
            ** function was called and the journal file does not exist.  */
            rc = pager_end_transaction(pPager, 0);
          }
        }
      }
      if( rc!=SQLITE_OK ){
        goto failed;
      }

      /* Reset the journal status fields to indicates that we have no
      ** rollback journal at this time. */
      pPager->journalStarted = 0;
      pPager->journalOff = 0;
      pPager->setMaster = 0;
      pPager->journalHdr = 0;
 
      /* Make sure the journal file has been synced to disk. */
 
      /* Playback and delete the journal.  Drop the database write
      ** lock and reacquire the read lock. Purge the cache before
      ** playing back the hot-journal so that we don't end up with
      ** an inconsistent cache.  Sync the hot journal before playing
      ** it back since the process that crashed and left the hot journal
      ** probably did not sync it and we are required to always sync
      ** the journal before playing it back.
      */
      if( isOpen(pPager->jfd) ){

        rc = pagerSyncHotJournal(pPager);
        if( rc==SQLITE_OK ){
          rc = pager_playback(pPager, 1);

        }




        if( rc!=SQLITE_OK ){
















          rc = pager_error(pPager, rc);
          goto failed;
        }
      }

      assert( (pPager->state==PAGER_SHARED)
           || (pPager->exclusiveMode && pPager->state>PAGER_SHARED)
      );
    }


    if( pPager->pBackup || sqlite3PcachePagecount(pPager->pPCache)>0 ){

      /* The shared-lock has just been acquired on the database file
      ** and there are already pages in the cache (from a previous
      ** read or write transaction).  Check to see if the database
      ** has been modified.  If the database has changed, flush the
      ** cache.
      **
      ** Database changes is detected by looking at 15 bytes beginning
................................................................................
      ** other bytes change randomly with each file change when
      ** a codec is in use.
      ** 
      ** There is a vanishingly small chance that a change will not be 
      ** detected.  The chance of an undetected change is so small that
      ** it can be neglected.
      */
      int nPage = 0;
      char dbFileVers[sizeof(pPager->dbFileVers)];
      sqlite3PagerPagecount(pPager, &nPage);

      if( pPager->errCode ){
        rc = pPager->errCode;

        goto failed;
      }

      if( nPage>0 ){
        IOTRACE(("CKVERS %p %d\n", pPager, sizeof(dbFileVers)));
        rc = sqlite3OsRead(pPager->fd, &dbFileVers, sizeof(dbFileVers), 24);
        if( rc!=SQLITE_OK ){
          goto failed;
        }
................................................................................
        memset(dbFileVers, 0, sizeof(dbFileVers));
      }

      if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
        pager_reset(pPager);
      }
    }
    assert( pPager->exclusiveMode || pPager->state==PAGER_SHARED );

    /* If there is a WAL file in the file-system, open this database in WAL
    ** mode. Otherwise, the following function call is a no-op.
    */
    rc = pagerOpenWalIfPresent(pPager);
  }









 failed:
  if( rc!=SQLITE_OK ){
    /* pager_unlock() is a no-op for exclusive mode and in-memory databases. */
    pager_unlock(pPager);



  }
  return rc;
}

/*
** If the reference count has reached zero, rollback any active
** transaction and unlock the pager.
**
** Except, in locking_mode=EXCLUSIVE when there is nothing to in
** the rollback journal, the unlock is not performed and there is
** nothing to rollback, so this routine is a no-op.
*/ 
static void pagerUnlockIfUnused(Pager *pPager){
  if( (sqlite3PcacheRefCount(pPager->pPCache)==0)
   && (!pPager->exclusiveMode || pPager->journalOff>0) 
  ){
    pagerUnlockAndRollback(pPager);
  }
}

/*
** Acquire a reference to page number pgno in pager pPager (a page
** reference has type DbPage*). If the requested reference is 
................................................................................
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int noContent       /* Do not bother reading content from disk if true */
){
  int rc;
  PgHdr *pPg;


  assert( assert_pager_state(pPager) );
  assert( pPager->state>PAGER_UNLOCK );

  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }

  /* If the pager is in the error state, return an error immediately. 
  ** Otherwise, request the page from the PCache layer. */
................................................................................
    assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) );
    PAGER_INCR(pPager->nHit);
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.  */
    int nMax;

    PAGER_INCR(pPager->nMiss);
    pPg = *ppPage;
    pPg->pPager = pPager;

    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
    ** number greater than this, or the unused locking-page, is requested. */
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto pager_acquire_err;
    }

    rc = sqlite3PagerPagecount(pPager, &nMax);
    if( rc!=SQLITE_OK ){
      goto pager_acquire_err;
    }

    if( MEMDB || nMax<(int)pgno || noContent || !isOpen(pPager->fd) ){
      if( pgno>pPager->mxPgno ){
        rc = SQLITE_FULL;
        goto pager_acquire_err;
      }
      if( noContent ){
        /* Failure to set the bits in the InJournal bit-vectors is benign.
        ** It merely means that we might do some extra work to journal a 
................................................................................
** has ever happened.
*/
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
  PgHdr *pPg = 0;
  assert( pPager!=0 );
  assert( pgno!=0 );
  assert( pPager->pPCache!=0 );
  assert( pPager->state > PAGER_UNLOCK );
  sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &pPg);
  return pPg;
}

/*
** Release a page reference.
**
................................................................................
**
** Return SQLITE_OK if everything is successful. Otherwise, return 
** SQLITE_NOMEM if the attempt to allocate Pager.pInJournal fails, or 
** an IO error code if opening or writing the journal file fails.
*/
static int pager_open_journal(Pager *pPager){
  int rc = SQLITE_OK;                        /* Return code */
  int nPage;                                 /* Size of database file */
  sqlite3_vfs * const pVfs = pPager->pVfs;   /* Local cache of vfs pointer */

  assert( pPager->state>=PAGER_RESERVED );
  assert( pPager->useJournal );
  assert( pPager->journalMode!=PAGER_JOURNALMODE_OFF );

  assert( pPager->pInJournal==0 );
  
  /* If already in the error state, this function is a no-op.  But on
  ** the other hand, this routine is never called if we are already in
  ** an error state. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  testcase( pPager->dbSizeValid==0 );
  rc = sqlite3PagerPagecount(pPager, &nPage);
  if( rc ) return rc;
  pPager->pInJournal = sqlite3BitvecCreate(nPage);
  if( pPager->pInJournal==0 ){
    return SQLITE_NOMEM;
  }

  /* Open the journal file if it is not already open. */
  if( !isOpen(pPager->jfd) ){
    if( pPager->journalMode==PAGER_JOURNALMODE_MEMORY ){
      sqlite3MemJournalOpen(pPager->jfd);
    }else{
      const int flags =                   /* VFS flags to open journal file */
        SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|
        (pPager->tempFile ? 
          (SQLITE_OPEN_DELETEONCLOSE|SQLITE_OPEN_TEMP_JOURNAL):
          (SQLITE_OPEN_MAIN_JOURNAL)
        );
#ifdef SQLITE_ENABLE_ATOMIC_WRITE
      rc = sqlite3JournalOpen(
          pVfs, pPager->zJournal, pPager->jfd, flags, jrnlBufferSize(pPager)
      );
#else
      rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, flags, 0);
#endif
    }
    assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
  }


  /* Write the first journal header to the journal file and open 
  ** the sub-journal if necessary.
  */
  if( rc==SQLITE_OK ){
    /* TODO: Check if all of these are really required. */
    pPager->dbOrigSize = pPager->dbSize;
    pPager->journalStarted = 0;
    pPager->needSync = 0;
    pPager->nRec = 0;
    pPager->journalOff = 0;
    pPager->setMaster = 0;
    pPager->journalHdr = 0;
    rc = writeJournalHdr(pPager);
  }


  if( rc!=SQLITE_OK ){
    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;



  }

  return rc;
}

/*
** Begin a write-transaction on the specified pager object. If a 
** write-transaction has already been opened, this function is a no-op.
**
** If the exFlag argument is false, then acquire at least a RESERVED
** lock on the database file. If exFlag is true, then acquire at least
** an EXCLUSIVE lock. If such a lock is already held, no locking 
** functions need be called.
**
** If this is not a temporary or in-memory file and, the journal file is 
** opened if it has not been already. For a temporary file, the opening 
** of the journal file is deferred until there is an actual need to 
** write to the journal. TODO: Why handle temporary files differently?
**
** If the journal file is opened (or if it is already open), then a
** journal-header is written to the start of it.
**
** If the subjInMemory argument is non-zero, then any sub-journal opened
** within this transaction will be opened as an in-memory file. This
** has no effect if the sub-journal is already opened (as it may be when
** running in exclusive mode) or if the transaction does not require a
** sub-journal. If the subjInMemory argument is zero, then any required
** sub-journal is implemented in-memory if pPager is an in-memory database, 
** or using a temporary file otherwise.
*/
int sqlite3PagerBegin(Pager *pPager, int exFlag, int subjInMemory){
  int rc = SQLITE_OK;
  assert( pPager->state!=PAGER_UNLOCK );
  pPager->subjInMemory = (u8)subjInMemory;

  if( pPager->state==PAGER_SHARED ){
    assert( pPager->pInJournal==0 );
    assert( !MEMDB && !pPager->tempFile );

    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = sqlite3OsLock(pPager->fd, EXCLUSIVE_LOCK);
        pPager->state = PAGER_SHARED;
        if( rc!=SQLITE_OK ){
          return rc;
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
      ** PAGER_RESERVED state. Otherwise, return an error code to the caller.
      ** The busy-handler is not invoked if another connection already
      ** holds the write-lock. If possible, the upper layer will call it.
      **
      ** WAL mode sets Pager.state to PAGER_RESERVED when it has an open
      ** transaction, but never to PAGER_EXCLUSIVE. This is because in 
      ** PAGER_EXCLUSIVE state the code to roll back savepoint transactions
      ** may copy data from the sub-journal into the database file as well
      ** as into the page cache. Which would be incorrect in WAL mode.
      */
      rc = sqlite3WalBeginWriteTransaction(pPager->pWal);
      if( rc==SQLITE_OK ){
        pPager->dbOrigSize = pPager->dbSize;
        pPager->state = PAGER_RESERVED;
        pPager->journalOff = 0;
      }

      assert( rc!=SQLITE_OK || pPager->state==PAGER_RESERVED );
      assert( rc==SQLITE_OK || pPager->state==PAGER_SHARED );
    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
      */
      rc = sqlite3OsLock(pPager->fd, RESERVED_LOCK);
      if( rc==SQLITE_OK ){
        pPager->state = PAGER_RESERVED;
        if( exFlag ){
          rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
        }
      }
    }

    /* No need to open the journal file at this time.  It will be
    ** opened before it is written to.  If we defer opening the journal,
    ** we might save the work of creating a file if the transaction
    ** ends up being a no-op.
    */

    if( rc!=SQLITE_OK ){
      assert( !pPager->dbModified );
      /* Ignore any IO error that occurs within pager_end_transaction(). The
      ** purpose of this call is to reset the internal state of the pager
      ** sub-system. It doesn't matter if the journal-file is not properly
      ** finalized at this point (since it is not a valid journal file anyway).
      */
      pager_end_transaction(pPager, 0);
    }


  }

  PAGERTRACE(("TRANSACTION %d\n", PAGERID(pPager)));
  return rc;
}

/*
................................................................................
** of any open savepoints as appropriate.
*/
static int pager_write(PgHdr *pPg){
  void *pData = pPg->pData;
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;

  /* This routine is not called unless a transaction has already been
  ** started.

  */
  assert( pPager->state>=PAGER_RESERVED );





  /* If an error has been previously detected, report the same error
  ** again.
  */

  if( NEVER(pPager->errCode) )  return pPager->errCode;

  /* Higher-level routines never call this function if database is not
  ** writable.  But check anyway, just for robustness. */
  if( NEVER(pPager->readOnly) ) return SQLITE_PERM;

  assert( !pPager->setMaster );

  CHECK_PAGE(pPg);

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  sqlite3PcacheMakeDirty(pPg);
  if( pageInJournal(pPg) && !subjRequiresPage(pPg) ){
    assert( !pagerUseWal(pPager) );
    pPager->dbModified = 1;
  }else{

    /* If we get this far, it means that the page needs to be
    ** written to the transaction journal or the ckeckpoint journal
    ** or both.
    **
    ** Higher level routines should have already started a transaction,
    ** which means they have acquired the necessary locks but the rollback
    ** journal might not yet be open.
    */
    assert( pPager->state>=RESERVED_LOCK );
    if( pPager->pInJournal==0
     && pPager->journalMode!=PAGER_JOURNALMODE_OFF 
     && !pagerUseWal(pPager)
    ){
      assert( pPager->useJournal );
      rc = pager_open_journal(pPager);
      if( rc!=SQLITE_OK ) return rc;
    }
    pPager->dbModified = 1;

  
    /* The transaction journal now exists and we have a RESERVED or an
    ** EXCLUSIVE lock on the main database file.  Write the current page to
    ** the transaction journal if it is not there already.
    */
    if( !pageInJournal(pPg) && isOpen(pPager->jfd) ){
      assert( !pagerUseWal(pPager) );
      if( pPg->pgno<=pPager->dbOrigSize ){
        u32 cksum;
        char *pData2;


        /* We should never write to the journal file the page that
        ** contains the database locks.  The following assert verifies
        ** that we do not. */
        assert( pPg->pgno!=PAGER_MJ_PGNO(pPager) );

        assert( pPager->journalHdr <= pPager->journalOff );
        CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
        cksum = pager_cksum(pPager, (u8*)pData2);










        rc = write32bits(pPager->jfd, pPager->journalOff, pPg->pgno);
        if( rc==SQLITE_OK ){
          rc = sqlite3OsWrite(pPager->jfd, pData2, pPager->pageSize,
                              pPager->journalOff + 4);
          pPager->journalOff += pPager->pageSize+4;
        }
        if( rc==SQLITE_OK ){
          rc = write32bits(pPager->jfd, pPager->journalOff, cksum);
          pPager->journalOff += 4;

        }
        IOTRACE(("JOUT %p %d %lld %d\n", pPager, pPg->pgno, 
                 pPager->journalOff, pPager->pageSize));
        PAGER_INCR(sqlite3_pager_writej_count);
        PAGERTRACE(("JOURNAL %d page %d needSync=%d hash(%08x)\n",
             PAGERID(pPager), pPg->pgno, 
             ((pPg->flags&PGHDR_NEED_SYNC)?1:0), pager_pagehash(pPg)));

        /* Even if an IO or diskfull error occurred while journalling the
        ** page in the block above, set the need-sync flag for the page.
        ** Otherwise, when the transaction is rolled back, the logic in
        ** playback_one_page() will think that the page needs to be restored
        ** in the database file. And if an IO error occurs while doing so,
        ** then corruption may follow.
        */
        if( !pPager->noSync ){
          pPg->flags |= PGHDR_NEED_SYNC;
          pPager->needSync = 1;
        }

        /* An error has occurred writing to the journal file. The 
        ** transaction will be rolled back by the layer above.
        */
        if( rc!=SQLITE_OK ){
          return rc;
        }

        pPager->nRec++;
        assert( pPager->pInJournal!=0 );
        rc = sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
        testcase( rc==SQLITE_NOMEM );
        assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
        rc |= addToSavepointBitvecs(pPager, pPg->pgno);
        if( rc!=SQLITE_OK ){
          assert( rc==SQLITE_NOMEM );
          return rc;
        }
      }else{
        if( !pPager->journalStarted && !pPager->noSync ){
          pPg->flags |= PGHDR_NEED_SYNC;
          pPager->needSync = 1;
        }
        PAGERTRACE(("APPEND %d page %d needSync=%d\n",
                PAGERID(pPager), pPg->pgno,
               ((pPg->flags&PGHDR_NEED_SYNC)?1:0)));
      }
    }
  
................................................................................
    if( subjRequiresPage(pPg) ){
      rc = subjournalPage(pPg);
    }
  }

  /* Update the database size and return.
  */
  assert( pPager->state>=PAGER_SHARED );
  if( pPager->dbSize<pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
................................................................................
int sqlite3PagerWrite(DbPage *pDbPage){
  int rc = SQLITE_OK;

  PgHdr *pPg = pDbPage;
  Pager *pPager = pPg->pPager;
  Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);





  if( nPagePerSector>1 ){
    Pgno nPageCount;          /* Total number of pages in database file */
    Pgno pg1;                 /* First page of the sector pPg is located on. */
    int nPage = 0;            /* Number of pages starting at pg1 to journal */
    int ii;                   /* Loop counter */
    int needSync = 0;         /* True if any page has PGHDR_NEED_SYNC */

................................................................................

    /* This trick assumes that both the page-size and sector-size are
    ** an integer power of 2. It sets variable pg1 to the identifier
    ** of the first page of the sector pPg is located on.
    */
    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

    rc = sqlite3PagerPagecount(pPager, (int *)&nPageCount);
    if( rc==SQLITE_OK ){
      if( pPg->pgno>nPageCount ){
        nPage = (pPg->pgno - pg1)+1;
      }else if( (pg1+nPagePerSector-1)>nPageCount ){
        nPage = nPageCount+1-pg1;
      }else{
        nPage = nPagePerSector;
      }
      assert(nPage>0);
      assert(pg1<=pPg->pgno);
      assert((pg1+nPage)>pPg->pgno);
    }

    for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
      Pgno pg = pg1+ii;
      PgHdr *pPage;
      if( pg==pPg->pgno || !sqlite3BitvecTest(pPager->pInJournal, pg) ){
        if( pg!=PAGER_MJ_PGNO(pPager) ){
          rc = sqlite3PagerGet(pPager, pg, &pPage);
          if( rc==SQLITE_OK ){
            rc = pager_write(pPage);
            if( pPage->flags&PGHDR_NEED_SYNC ){
              needSync = 1;
              assert(pPager->needSync);
            }
            sqlite3PagerUnref(pPage);
          }
        }
      }else if( (pPage = pager_lookup(pPager, pg))!=0 ){
        if( pPage->flags&PGHDR_NEED_SYNC ){
          needSync = 1;
................................................................................
    /* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages 
    ** starting at pg1, then it needs to be set for all of them. Because
    ** writing to any of these nPage pages may damage the others, the
    ** journal file must contain sync()ed copies of all of them
    ** before any of them can be written out to the database file.
    */
    if( rc==SQLITE_OK && needSync ){
      assert( !MEMDB && pPager->noSync==0 );
      for(ii=0; ii<nPage; ii++){
        PgHdr *pPage = pager_lookup(pPager, pg1+ii);
        if( pPage ){
          pPage->flags |= PGHDR_NEED_SYNC;
          sqlite3PagerUnref(pPage);
        }
      }
      assert(pPager->needSync);
    }

    assert( pPager->doNotSyncSpill==1 );
    pPager->doNotSyncSpill--;
  }else{
    rc = pager_write(pDbPage);
  }
................................................................................
** with the SQLITE_ENABLE_ATOMIC_WRITE macro defined. In this case,
** if isDirect is non-zero, then the database file is updated directly
** by writing an updated version of page 1 using a call to the 
** sqlite3OsWrite() function.
*/
static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
  int rc = SQLITE_OK;






  /* Declare and initialize constant integer 'isDirect'. If the
  ** atomic-write optimization is enabled in this build, then isDirect
  ** is initialized to the value passed as the isDirectMode parameter
  ** to this function. Otherwise, it is always set to zero.
  **
  ** The idea is that if the atomic-write optimization is not
................................................................................
# define DIRECT_MODE 0
  assert( isDirectMode==0 );
  UNUSED_PARAMETER(isDirectMode);
#else
# define DIRECT_MODE isDirectMode
#endif

  assert( pPager->state>=PAGER_RESERVED );
  if( !pPager->changeCountDone && pPager->dbSize>0 ){
    PgHdr *pPgHdr;                /* Reference to page 1 */
    u32 change_counter;           /* Initial value of change-counter field */

    assert( !pPager->tempFile && isOpen(pPager->fd) );

    /* Open page 1 of the file for writing. */
................................................................................
** If the EXCLUSIVE lock is already held or the attempt to obtain it is
** successful, or the connection is in WAL mode, SQLITE_OK is returned.
** Otherwise, either SQLITE_BUSY or an SQLITE_IOERR_XXX error code is 
** returned.
*/
int sqlite3PagerExclusiveLock(Pager *pPager){
  int rc = SQLITE_OK;
  assert( pPager->state>=PAGER_RESERVED );




  if( 0==pagerUseWal(pPager) ){
    rc = pager_wait_on_lock(pPager, PAGER_EXCLUSIVE);
  }
  return rc;
}

/*
** Sync the database file for the pager pPager. zMaster points to the name
** of a master journal file that should be written into the individual
................................................................................
int sqlite3PagerCommitPhaseOne(
  Pager *pPager,                  /* Pager object */
  const char *zMaster,            /* If not NULL, the master journal name */
  int noSync                      /* True to omit the xSync on the db file */
){
  int rc = SQLITE_OK;             /* Return code */

  /* The dbOrigSize is never set if journal_mode=OFF */
  assert( pPager->journalMode!=PAGER_JOURNALMODE_OFF || pPager->dbOrigSize==0 );





  /* If a prior error occurred, report that error again. */
  if( pPager->errCode ) return pPager->errCode;

  PAGERTRACE(("DATABASE SYNC: File=%s zMaster=%s nSize=%d\n", 
      pPager->zFilename, zMaster, pPager->dbSize));




  if( MEMDB && pPager->dbModified ){
    /* If this is an in-memory db, or no pages have been written to, or this
    ** function has already been called, it is mostly a no-op.  However, any
    ** backup in progress needs to be restarted.
    */
    sqlite3BackupRestart(pPager->pBackup);
  }else if( pPager->dbModified ){
    if( pagerUseWal(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      if( pList ){
        rc = pagerWalFrames(pPager, pList, pPager->dbSize, 1, 
            (pPager->fullSync ? pPager->sync_flags : 0)
        );
      }
................................................................................
      PgHdr *pPg;
      assert( isOpen(pPager->jfd) 
           || pPager->journalMode==PAGER_JOURNALMODE_OFF 
           || pPager->journalMode==PAGER_JOURNALMODE_WAL 
      );
      if( !zMaster && isOpen(pPager->jfd) 
       && pPager->journalOff==jrnlBufferSize(pPager) 
       && pPager->dbSize>=pPager->dbFileSize
       && (0==(pPg = sqlite3PcacheDirtyList(pPager->pPCache)) || 0==pPg->pDirty)
      ){
        /* Update the db file change counter via the direct-write method. The 
        ** following call will modify the in-memory representation of page 1 
        ** to include the updated change counter and then write page 1 
        ** directly to the database file. Because of the atomic-write 
        ** property of the host file-system, this is safe.
................................................................................
      ** reading data from the database file.
      **
      ** When journal_mode==OFF the dbOrigSize is always zero, so this
      ** block never runs if journal_mode=OFF.
      */
  #ifndef SQLITE_OMIT_AUTOVACUUM
      if( pPager->dbSize<pPager->dbOrigSize 
       && ALWAYS(pPager->journalMode!=PAGER_JOURNALMODE_OFF)
      ){
        Pgno i;                                   /* Iterator variable */
        const Pgno iSkip = PAGER_MJ_PGNO(pPager); /* Pending lock page */
        const Pgno dbSize = pPager->dbSize;       /* Database image size */ 
        pPager->dbSize = pPager->dbOrigSize;
        for( i=dbSize+1; i<=pPager->dbOrigSize; i++ ){
          if( !sqlite3BitvecTest(pPager->pInJournal, i) && i!=iSkip ){
................................................................................
      /* Write the master journal name into the journal file. If a master 
      ** journal file name has already been written to the journal file, 
      ** or if zMaster is NULL (no master journal), then this call is a no-op.
      */
      rc = writeMasterJournal(pPager, zMaster);
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  

      /* Sync the journal file. If the atomic-update optimization is being
      ** used, this call will not create the journal file or perform any
      ** real IO.







      */
      rc = syncJournal(pPager);
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  
      /* Write all dirty pages to the database file. */
      rc = pager_write_pagelist(pPager,sqlite3PcacheDirtyList(pPager->pPCache));
      if( rc!=SQLITE_OK ){
        assert( rc!=SQLITE_IOERR_BLOCKED );
        goto commit_phase_one_exit;
      }
      sqlite3PcacheCleanAll(pPager->pPCache);
  
      /* If the file on disk is not the same size as the database image,
      ** then use pager_truncate to grow or shrink the file here.
      */
      if( pPager->dbSize!=pPager->dbFileSize ){
        Pgno nNew = pPager->dbSize - (pPager->dbSize==PAGER_MJ_PGNO(pPager));
        assert( pPager->state>=PAGER_EXCLUSIVE );
        rc = pager_truncate(pPager, nNew);
        if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
      }
  
      /* Finally, sync the database file. */
      if( !pPager->noSync && !noSync ){
        rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
      }
      IOTRACE(("DBSYNC %p\n", pPager))
    }

    assert( pPager->state!=PAGER_SYNCED );
    pPager->state = PAGER_SYNCED;
  }

commit_phase_one_exit:



  return rc;
}


/*
** When this function is called, the database file has been completely
** updated to reflect the changes made by the current transaction and
................................................................................
  int rc = SQLITE_OK;                  /* Return code */

  /* This routine should not be called if a prior error has occurred.
  ** But if (due to a coding error elsewhere in the system) it does get
  ** called, just return the same error code without doing anything. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  /* This function should not be called if the pager is not in at least
  ** PAGER_RESERVED state. **FIXME**: Make it so that this test always
  ** fails - make it so that we never reach this point if we do not hold
  ** all necessary locks.
  */
  if( NEVER(pPager->state<PAGER_RESERVED) ) return SQLITE_ERROR;

  /* An optimization. If the database was not actually modified during
  ** this transaction, the pager is running in exclusive-mode and is
  ** using persistent journals, then this function is a no-op.
  **
  ** The start of the journal file currently contains a single journal 
  ** header with the nRec field set to 0. If such a journal is used as
  ** a hot-journal during hot-journal rollback, 0 changes will be made
  ** to the database file. So there is no need to zero the journal 
  ** header. Since the pager is in exclusive mode, there is no need
  ** to drop any locks either.
  */

  if( pPager->dbModified==0 && pPager->exclusiveMode 
   && pPager->journalMode==PAGER_JOURNALMODE_PERSIST
  ){
    assert( pPager->journalOff==JOURNAL_HDR_SZ(pPager) || !pPager->journalOff );

    return SQLITE_OK;
  }

  PAGERTRACE(("COMMIT %d\n", PAGERID(pPager)));
  assert( pPager->state==PAGER_SYNCED || MEMDB || !pPager->dbModified );
  rc = pager_end_transaction(pPager, pPager->setMaster);
  return pager_error(pPager, rc);
}

/*
** Rollback all changes. The database falls back to PAGER_SHARED mode.



**



** This function performs two tasks:
**
**   1) It rolls back the journal file, restoring all database file and 
**      in-memory cache pages to the state they were in when the transaction
**      was opened, and

**   2) It finalizes the journal file, so that it is not used for hot
**      rollback at any point in the future.
**
** subject to the following qualifications:

**
** * If the journal file is not yet open when this function is called,
**   then only (2) is performed. In this case there is no journal file
**   to roll back.
**
** * If in an error state other than SQLITE_FULL, then task (1) is 
**   performed. If successful, task (2). Regardless of the outcome
**   of either, the error state error code is returned to the caller
**   (i.e. either SQLITE_IOERR or SQLITE_CORRUPT).
**
** * If the pager is in PAGER_RESERVED state, then attempt (1). Whether
**   or not (1) is successful, also attempt (2). If successful, return
**   SQLITE_OK. Otherwise, enter the error state and return the first 
**   error code encountered. 
**
**   In this case there is no chance that the database was written to. 
**   So is safe to finalize the journal file even if the playback 
**   (operation 1) failed. However the pager must enter the error state
**   as the contents of the in-memory cache are now suspect.
**
** * Finally, if in PAGER_EXCLUSIVE state, then attempt (1). Only
**   attempt (2) if (1) is successful. Return SQLITE_OK if successful,
**   otherwise enter the error state and return the error code from the 
**   failing operation.
**
**   In this case the database file may have been written to. So if the
**   playback operation did not succeed it would not be safe to finalize
**   the journal file. It needs to be left in the file-system so that
**   some other process can use it to restore the database state (by
**   hot-journal rollback).
*/
int sqlite3PagerRollback(Pager *pPager){
  int rc = SQLITE_OK;                  /* Return code */
  PAGERTRACE(("ROLLBACK %d\n", PAGERID(pPager)));









  if( pagerUseWal(pPager) ){
    int rc2;

    rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
    rc2 = pager_end_transaction(pPager, pPager->setMaster);
    if( rc==SQLITE_OK ) rc = rc2;
    rc = pager_error(pPager, rc);
  }else if( !pPager->dbModified || !isOpen(pPager->jfd) ){
    rc = pager_end_transaction(pPager, pPager->setMaster);
  }else if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
    if( pPager->state>=PAGER_EXCLUSIVE ){
      pager_playback(pPager, 0);
    }
    rc = pPager->errCode;
  }else{
    if( pPager->state==PAGER_RESERVED ){
      int rc2;
      rc = pager_playback(pPager, 0);
      rc2 = pager_end_transaction(pPager, pPager->setMaster);
      if( rc==SQLITE_OK ){
        rc = rc2;
      }
    }else{
      rc = pager_playback(pPager, 0);
    }



    if( !MEMDB ){
      pPager->dbSizeValid = 0;
    }

    /* If an error occurs during a ROLLBACK, we can no longer trust the pager
    ** cache. So call pager_error() on the way out to make any error 
    ** persistent.
    */
    rc = pager_error(pPager, rc);
  }
  return rc;
}

/*
** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
u8 sqlite3PagerIsreadonly(Pager *pPager){
................................................................................
** This routine is used for testing and analysis only.
*/
int *sqlite3PagerStats(Pager *pPager){
  static int a[11];
  a[0] = sqlite3PcacheRefCount(pPager->pPCache);
  a[1] = sqlite3PcachePagecount(pPager->pPCache);
  a[2] = sqlite3PcacheGetCachesize(pPager->pPCache);
  a[3] = pPager->dbSizeValid ? (int) pPager->dbSize : -1;
  a[4] = pPager->state;
  a[5] = pPager->errCode;
  a[6] = pPager->nHit;
  a[7] = pPager->nMiss;
  a[8] = 0;  /* Used to be pPager->nOvfl */
  a[9] = pPager->nRead;
  a[10] = pPager->nWrite;
  return a;
................................................................................
** If a memory allocation fails, SQLITE_NOMEM is returned. If an error 
** occurs while opening the sub-journal file, then an IO error code is
** returned. Otherwise, SQLITE_OK.
*/
int sqlite3PagerOpenSavepoint(Pager *pPager, int nSavepoint){
  int rc = SQLITE_OK;                       /* Return code */
  int nCurrent = pPager->nSavepoint;        /* Current number of savepoints */




  if( nSavepoint>nCurrent && pPager->useJournal ){
    int ii;                                 /* Iterator variable */
    PagerSavepoint *aNew;                   /* New Pager.aSavepoint array */
    int nPage;                              /* Size of database file */

    rc = sqlite3PagerPagecount(pPager, &nPage);
    if( rc ) return rc;

    /* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
    ** if the allocation fails. Otherwise, zero the new portion in case a 
    ** malloc failure occurs while populating it in the for(...) loop below.
    */
    aNew = (PagerSavepoint *)sqlite3Realloc(
        pPager->aSavepoint, sizeof(PagerSavepoint)*nSavepoint
................................................................................
      return SQLITE_NOMEM;
    }
    memset(&aNew[nCurrent], 0, (nSavepoint-nCurrent) * sizeof(PagerSavepoint));
    pPager->aSavepoint = aNew;

    /* Populate the PagerSavepoint structures just allocated. */
    for(ii=nCurrent; ii<nSavepoint; ii++){
      aNew[ii].nOrig = nPage;
      if( isOpen(pPager->jfd) && pPager->journalOff>0 ){
        aNew[ii].iOffset = pPager->journalOff;
      }else{
        aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
      }
      aNew[ii].iSubRec = pPager->nSubRec;
      aNew[ii].pInSavepoint = sqlite3BitvecCreate(nPage);
      if( !aNew[ii].pInSavepoint ){
        return SQLITE_NOMEM;
      }
      if( pagerUseWal(pPager) ){
        sqlite3WalSavepoint(pPager->pWal, aNew[ii].aWalData);
      }
      pPager->nSavepoint = ii+1;
................................................................................
** then savepoint iSavepoint is also destroyed.
**
** This function may return SQLITE_NOMEM if a memory allocation fails,
** or an IO error code if an IO error occurs while rolling back a 
** savepoint. If no errors occur, SQLITE_OK is returned.
*/ 
int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint){
  int rc = SQLITE_OK;

  assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
  assert( iSavepoint>=0 || op==SAVEPOINT_ROLLBACK );

  if( iSavepoint<pPager->nSavepoint ){
    int ii;            /* Iterator variable */
    int nNew;          /* Number of remaining savepoints after this op. */

    /* Figure out how many savepoints will still be active after this
    ** operation. Store this value in nNew. Then free resources associated 
    ** with any savepoints that are destroyed by this operation.
    */
................................................................................
    ** the database file, so the playback operation can be skipped.
    */
    else if( pagerUseWal(pPager) || isOpen(pPager->jfd) ){
      PagerSavepoint *pSavepoint = (nNew==0)?0:&pPager->aSavepoint[nNew-1];
      rc = pagerPlaybackSavepoint(pPager, pSavepoint);
      assert(rc!=SQLITE_DONE);
    }
  
  }
  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3PagerFilename(Pager *pPager){
................................................................................
int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
  PgHdr *pPgOld;               /* The page being overwritten. */
  Pgno needSyncPgno = 0;       /* Old value of pPg->pgno, if sync is required */
  int rc;                      /* Return code */
  Pgno origPgno;               /* The original page number */

  assert( pPg->nRef>0 );





  /* In order to be able to rollback, an in-memory database must journal
  ** the page we are moving from.
  */
  if( MEMDB ){
    rc = sqlite3PagerWrite(pPg);
    if( rc ) return rc;
................................................................................
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( pageInJournal(pPg) || pPg->pgno>pPager->dbOrigSize );
    assert( pPg->flags&PGHDR_DIRTY );
    assert( pPager->needSync );
  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PgHdr.needSync was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.
  */
  pPg->flags &= ~PGHDR_NEED_SYNC;
  pPgOld = pager_lookup(pPager, pgno);
  assert( !pPgOld || pPgOld->nRef==1 );
  if( pPgOld ){
    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
    if( MEMDB ){
      /* Do not discard pages from an in-memory database since we might
      ** need to rollback later.  Just move the page out of the way. */
      assert( pPager->dbSizeValid );
      sqlite3PcacheMove(pPgOld, pPager->dbSize+1);
    }else{
      sqlite3PcacheDrop(pPgOld);
    }
  }

  origPgno = pPg->pgno;
  sqlite3PcacheMove(pPg, pgno);
  sqlite3PcacheMakeDirty(pPg);
  pPager->dbModified = 1;











  if( needSyncPgno ){
    /* If needSyncPgno is non-zero, then the journal file needs to be 
    ** sync()ed before any data is written to database file page needSyncPgno.
    ** Currently, no such page exists in the page-cache and the 
    ** "is journaled" bitvec flag has been set. This needs to be remedied by
    ** loading the page into the pager-cache and setting the PgHdr.needSync 
    ** flag.
    **
    ** If the attempt to load the page into the page-cache fails, (due
    ** to a malloc() or IO failure), clear the bit in the pInJournal[]
    ** array. Otherwise, if the page is loaded and written again in
    ** this transaction, it may be written to the database file before
    ** it is synced into the journal file. This way, it may end up in
    ** the journal file twice, but that is not a problem.
    **
    ** The sqlite3PagerGet() call may cause the journal to sync. So make
    ** sure the Pager.needSync flag is set too.
    */
    PgHdr *pPgHdr;
    assert( pPager->needSync );
    rc = sqlite3PagerGet(pPager, needSyncPgno, &pPgHdr);
    if( rc!=SQLITE_OK ){
      if( needSyncPgno<=pPager->dbOrigSize ){
        assert( pPager->pTmpSpace!=0 );
        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno, pPager->pTmpSpace);
      }
      return rc;
    }
    pPager->needSync = 1;
    assert( pPager->noSync==0 && !MEMDB );
    pPgHdr->flags |= PGHDR_NEED_SYNC;
    sqlite3PcacheMakeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }

  /*
  ** For an in-memory database, make sure the original page continues
  ** to exist, in case the transaction needs to roll back.  Use pPgOld
  ** as the original page since it has already been allocated.
  */
  if( MEMDB ){
    sqlite3PcacheMove(pPgOld, origPgno);
    sqlite3PagerUnref(pPgOld);
  }

  return SQLITE_OK;
}
#endif

/*
** Return a pointer to the data for the specified page.
*/
................................................................................
    assert( eOld==PAGER_JOURNALMODE_MEMORY || eOld==PAGER_JOURNALMODE_OFF );
    if( eMode!=PAGER_JOURNALMODE_MEMORY && eMode!=PAGER_JOURNALMODE_OFF ){
      eMode = eOld;
    }
  }

  if( eMode!=eOld ){
    /* When changing between rollback modes, close the journal file prior
    ** to the change.  But when changing from a rollback mode to WAL, keep
    ** the journal open since there is a rollback-style transaction in play
    ** used to convert the version numbers in the btree header.
    */
    if( isOpen(pPager->jfd) && eMode!=PAGER_JOURNALMODE_WAL ){
      sqlite3OsClose(pPager->jfd);
    }

    /* Change the journal mode. */

    pPager->journalMode = (u8)eMode;

    /* When transistioning from TRUNCATE or PERSIST to any other journal
    ** mode except WAL (and we are not in locking_mode=EXCLUSIVE) then 
    ** delete the journal file.
    */
    assert( (PAGER_JOURNALMODE_TRUNCATE & 5)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST & 5)==1 );
    assert( (PAGER_JOURNALMODE_DELETE & 5)==0 );
    assert( (PAGER_JOURNALMODE_MEMORY & 5)==4 );
    assert( (PAGER_JOURNALMODE_OFF & 5)==0 );
................................................................................
      ** not possible, then that is not a problem. Deleting the journal file
      ** here is an optimization only.
      **
      ** Before deleting the journal file, obtain a RESERVED lock on the
      ** database file. This ensures that the journal file is not deleted
      ** while it is in use by some other client.
      */




      int rc = SQLITE_OK;
      int state = pPager->state;
      if( state<PAGER_SHARED ){
        rc = sqlite3PagerSharedLock(pPager);
      }
      if( pPager->state==PAGER_SHARED ){

        assert( rc==SQLITE_OK );
        rc = sqlite3OsLock(pPager->fd, RESERVED_LOCK);
      }
      if( rc==SQLITE_OK ){
        sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }
      if( rc==SQLITE_OK && state==PAGER_SHARED ){
        sqlite3OsUnlock(pPager->fd, SHARED_LOCK);
      }else if( state==PAGER_UNLOCK ){
        pager_unlock(pPager);
      }
      assert( state==pPager->state );

    }
  }

  /* Return the new journal mode */
  return (int)pPager->journalMode;
}

................................................................................

/*
** Return TRUE if the pager is in a state where it is OK to change the
** journalmode.  Journalmode changes can only happen when the database
** is unmodified.
*/
int sqlite3PagerOkToChangeJournalMode(Pager *pPager){
  if( pPager->dbModified ) return 0;

  if( NEVER(isOpen(pPager->jfd) && pPager->journalOff>0) ) return 0;
  return 1;
}

/*
** Get/set the size-limit used for persistent journal files.
**
................................................................................
** The caller must be holding a SHARED lock on the database file to call
** this function.
**
** If the pager passed as the first argument is open on a real database
** file (not a temp file or an in-memory database), and the WAL file
** is not already open, make an attempt to open it now. If successful,
** return SQLITE_OK. If an error occurs or the VFS used by the pager does 
** not support the xShmXXX() methods, return an error code. *pisOpen is
** not modified in either case.
**
** If the pager is open on a temp-file (or in-memory database), or if
** the WAL file is already open, set *pisOpen to 1 and return SQLITE_OK
** without doing anything.
*/
int sqlite3PagerOpenWal(
  Pager *pPager,                  /* Pager object */
  int *pisOpen                    /* OUT: Set to true if call is a no-op */
){
  int rc = SQLITE_OK;             /* Return code */


  assert( pPager->state>=PAGER_SHARED );


  assert( (pisOpen==0 && !pPager->tempFile && !pPager->pWal) || *pisOpen==0 );

  if( !pPager->tempFile && !pPager->pWal ){
    if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;





    /* Open the connection to the log file. If this operation fails, 
    ** (e.g. due to malloc() failure), unlock the database file and 
    ** return an error code.
    */
    rc = sqlite3WalOpen(pPager->pVfs, pPager->fd, pPager->zWal, &pPager->pWal);
    if( rc==SQLITE_OK ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;

    }
  }else{
    *pisOpen = 1;
  }

  return rc;
}

/*
** This function is called to close the connection to the log file prior
................................................................................

  /* If the log file is not already open, but does exist in the file-system,
  ** it may need to be checkpointed before the connection can switch to
  ** rollback mode. Open it now so this can happen.
  */
  if( !pPager->pWal ){
    int logexists = 0;
    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_SHARED);
    if( rc==SQLITE_OK ){
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &logexists
      );
    }
    if( rc==SQLITE_OK && logexists ){
      rc = sqlite3WalOpen(pPager->pVfs, pPager->fd,
................................................................................
    }
  }
    
  /* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
  ** the database file, the log and log-summary files will be deleted.
  */
  if( rc==SQLITE_OK && pPager->pWal ){
    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal,
                           (pPager->noSync ? 0 : pPager->sync_flags), 
        pPager->pageSize, (u8*)pPager->pTmpSpace
      );
      pPager->pWal = 0;
    }else{
      /* If we cannot get an EXCLUSIVE lock, downgrade the PENDING lock
      ** that we did get back to SHARED. */
      sqlite3OsUnlock(pPager->fd, SQLITE_LOCK_SHARED);
    }
  }
  return rc;
}

#ifdef SQLITE_HAS_CODEC
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630
631
632
633
634
635
636


637
638
639
640

641
642
643
644
645
646
647
648
649
650
651
652
...
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804


805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
....
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030

1031
1032
1033
1034



1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053

1054
1055
1056
1057
1058
1059
1060
1061
1062


1063
1064
1065

1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
....
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
....
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
....
1597
1598
1599
1600
1601
1602
1603

1604
1605
1606
1607
1608
1609
1610
....
1632
1633
1634
1635
1636
1637
1638
1639



1640
1641

1642
1643


1644
1645
1646
1647
1648
1649
1650
....
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
....
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788

1789
1790
1791
1792
1793
1794
1795
....
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809


























1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
....
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852




1853
1854
1855
1856
1857
1858
1859
....
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884

1885
1886
1887
1888
1889
1890
1891
1892
1893
....
1895
1896
1897
1898
1899
1900
1901

1902
1903
1904
1905

1906

1907
1908
1909
1910
1911
1912
1913
....
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933

1934


1935
1936
1937


1938
1939
1940
1941
1942
1943
1944

1945


1946
1947
1948


1949
1950
1951
1952
1953
1954
1955

1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981

1982
1983
1984
1985
1986
1987
1988
1989
1990
....
2028
2029
2030
2031
2032
2033
2034
2035
2036

2037
2038
2039
2040
2041
2042
2043
....
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
....
2130
2131
2132
2133
2134
2135
2136

2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
....
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
....
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
....
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576

2577
2578
2579
2580
2581
2582
2583
....
2719
2720
2721
2722
2723
2724
2725
2726
2727


2728
2729
2730
2731
2732
2733
2734
2735
....
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
....
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943


2944

2945

2946

2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017


3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031

3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046



3047
3048
3049
3050
3051
3052
3053
....
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
....
3231
3232
3233
3234
3235
3236
3237

3238
3239
3240
3241
3242
3243
3244
....
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
....
3399
3400
3401
3402
3403
3404
3405

3406
3407
3408
3409

3410
3411
3412
3413
3414
3415
3416
3417
....
3468
3469
3470
3471
3472
3473
3474
3475
3476

3477
3478
3479









3480
3481




























3482
3483
3484















3485
3486
3487
3488
3489
3490
3491
....
3499
3500
3501
3502
3503
3504
3505











3506
3507
3508
3509
3510
3511
3512
3513
3514
3515



3516

3517
3518





3519
3520
3521
3522
3523
3524
3525
....
3556
3557
3558
3559
3560
3561
3562

3563
3564
3565
3566
3567
3568
3569
3570
3571
....
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628

3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
....
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
....
3703
3704
3705
3706
3707
3708
3709



3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728

3729
3730
3731
3732
3733
3734
3735
....
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809





3810
3811

3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
....
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860















3861
3862
3863

3864
3865
3866
3867
3868
3869
3870
....
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
....
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
....
4056
4057
4058
4059
4060
4061
4062
4063
4064




4065



4066
4067
4068
4069
4070
4071
4072
4073
....
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
....
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
....
4364
4365
4366
4367
4368
4369
4370

4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387

4388
4389
4390
4391
4392
4393
4394
....
4445
4446
4447
4448
4449
4450
4451

4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
....
4563
4564
4565
4566
4567
4568
4569

4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580




4581
4582

4583
4584
4585

4586








4587



4588
4589


4590
4591
4592
4593

4594
4595
4596
4597
4598

4599
4600
4601
4602
4603

4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619

4620
4621

4622
4623

4624

4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638

4639
4640
4641
4642
4643

4644
4645
4646
4647
4648
4649
4650
4651
4652







4653
4654













4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
....
4714
4715
4716
4717
4718
4719
4720
4721
4722

4723


4724
4725

4726
4727
4728
4729
4730
4731
4732
....
4734
4735
4736
4737
4738
4739
4740

4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757

4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775


4776
4777
4778
4779
4780
4781
4782
....
4832
4833
4834
4835
4836
4837
4838
4839
4840

4841
4842
4843
4844
4845
4846
4847
....
4867
4868
4869
4870
4871
4872
4873

4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885





4886
4887
4888
4889
4890
4891
4892
4893
....
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
....
4990
4991
4992
4993
4994
4995
4996

4997
4998

4999

5000
5001
5002
5003
5004
5005
5006
5007
5008


5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041



5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069








5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084

5085
5086
5087
5088
5089
5090
5091

5092
5093
5094
5095
5096
5097
5098
5099
5100
5101






5102
5103








5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
....
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164


5165
5166
5167
5168
5169
5170
5171


5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190

5191




5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229



5230
5231

5232
5233
5234
5235
5236
5237
5238
5239
5240
5241


















5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254

5255
5256
5257
5258
5259
5260
5261
....
5267
5268
5269
5270
5271
5272
5273

5274
5275
5276
5277
5278
5279
5280
....
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
....
5319
5320
5321
5322
5323
5324
5325
5326

5327
5328
5329
5330
5331
5332
5333
5334
5335
5336

5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347

5348
5349
5350
5351
5352
5353
5354
....
5360
5361
5362
5363
5364
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** associated file-descriptor is returned. FILEHANDLEID() takes an sqlite3_file
** struct as its argument.
*/
#define PAGERID(p) ((int)(p->fd))
#define FILEHANDLEID(fd) ((int)fd)

/*
** The Pager.eState variable stores the current 'state' of a pager. A
** pager may be in any one of the seven states shown in the following
** state diagram.
**

**                            OPEN <------+------+
**                              |         |      |
**                              V         |      |
**               +---------> READER-------+      |
**               |              |                |
**               |              V                |
**               |<-------WRITER_LOCKED------> ERROR
**               |              |                ^  
**               |              V                |
**               |<------WRITER_CACHEMOD-------->|
**               |              |                |
**               |              V                |
**               |<-------WRITER_DBMOD---------->|
**               |              |                |
**               |              V                |
**               +<------WRITER_FINISHED-------->+
**

**
** List of state transitions and the C [function] that performs each:

** 
**   OPEN              -> READER              [sqlite3PagerSharedLock]
**   READER            -> OPEN                [pager_unlock]
**
**   READER            -> WRITER_LOCKED       [sqlite3PagerBegin]
**   WRITER_LOCKED     -> WRITER_CACHEMOD     [pager_open_journal]
**   WRITER_CACHEMOD   -> WRITER_DBMOD        [syncJournal]
**   WRITER_DBMOD      -> WRITER_FINISHED     [sqlite3PagerCommitPhaseOne]
**   WRITER_***        -> READER              [pager_end_transaction]
**

**   WRITER_***        -> ERROR               [pager_error]
**   ERROR             -> OPEN                [pager_unlock]
** 
**
**  OPEN:
**
**    The pager starts up in this state. Nothing is guaranteed in this
**    state - the file may or may not be locked and the database size is
**    unknown. The database may not be read or written.
**
**    * No read or write transaction is active.
**    * Any lock, or no lock at all, may be held on the database file.
**    * The dbSize, dbOrigSize and dbFileSize variables may not be trusted.
**
**  READER:
**
**    In this state all the requirements for reading the database in 
**    rollback (non-WAL) mode are met. Unless the pager is (or recently
**    was) in exclusive-locking mode, a user-level read transaction is 
**    open. The database size is known in this state.
**
**    A connection running with locking_mode=normal enters this state when
**    it opens a read-transaction on the database and returns to state
**    OPEN after the read-transaction is completed. However a connection
**    running in locking_mode=exclusive (including temp databases) remains in
**    this state even after the read-transaction is closed. The only way
**    a locking_mode=exclusive connection can transition from READER to OPEN
**    is via the ERROR state (see below).
** 
**    * A read transaction may be active (but a write-transaction cannot).
**    * A SHARED or greater lock is held on the database file.
**    * The dbSize variable may be trusted (even if a user-level read 
**      transaction is not active). The dbOrigSize and dbFileSize variables
**      may not be trusted at this point.
**    * If the database is a WAL database, then the WAL connection is open.
**    * Even if a read-transaction is not open, it is guaranteed that 
**      there is no hot-journal in the file-system.
**
**  WRITER_LOCKED:
**
**    The pager moves to this state from READER when a write-transaction
**    is first opened on the database. In WRITER_LOCKED state, all locks 
**    required to start a write-transaction are held, but no actual 
**    modifications to the cache or database have taken place.
**
**    In rollback mode, a RESERVED or (if the transaction was opened with 
**    BEGIN EXCLUSIVE) EXCLUSIVE lock is obtained on the database file when
**    moving to this state, but the journal file is not written to or opened 
**    to in this state. If the transaction is committed or rolled back while 
**    in WRITER_LOCKED state, all that is required is to unlock the database 
**    file.
**
**    IN WAL mode, WalBeginWriteTransaction() is called to lock the log file.
**    If the connection is running with locking_mode=exclusive, an attempt
**    is made to obtain an EXCLUSIVE lock on the database file.
**
**    * A write transaction is active.
**    * If the connection is open in rollback-mode, a RESERVED or greater 
**      lock is held on the database file.
**    * If the connection is open in WAL-mode, a WAL write transaction
**      is open (i.e. sqlite3WalBeginWriteTransaction() has been successfully
**      called).
**    * The dbSize, dbOrigSize and dbFileSize variables are all valid.
**    * The contents of the pager cache have not been modified.
**    * The journal file may or may not be open.
**    * Nothing (not even the first header) has been written to the journal.
**
**  WRITER_CACHEMOD:
**
**    A pager moves from WRITER_LOCKED state to this state when a page is
**    first modified by the upper layer. In rollback mode the journal file
**    is opened (if it is not already open) and a header written to the
**    start of it. The database file on disk has not been modified.
**
**    * A write transaction is active.
**    * A RESERVED or greater lock is held on the database file.
**    * The journal file is open and the first header has been written 
**      to it, but the header has not been synced to disk.
**    * The contents of the page cache have been modified.
**
**  WRITER_DBMOD:
**
**    The pager transitions from WRITER_CACHEMOD into WRITER_DBMOD state
**    when it modifies the contents of the database file. WAL connections
**    never enter this state (since they do not modify the database file,
**    just the log file).
**
**    * A write transaction is active.
**    * An EXCLUSIVE or greater lock is held on the database file.
**    * The journal file is open and the first header has been written 
**      and synced to disk.
**    * The contents of the page cache have been modified (and possibly
**      written to disk).
**
**  WRITER_FINISHED:
**
**    It is not possible for a WAL connection to enter this state.
**
**    A rollback-mode pager changes to WRITER_FINISHED state from WRITER_DBMOD
**    state after the entire transaction has been successfully written into the
**    database file. In this state the transaction may be committed simply
**    by finalizing the journal file. Once in WRITER_FINISHED state, it is 
**    not possible to modify the database further. At this point, the upper 
**    layer must either commit or rollback the transaction.
**
**    * A write transaction is active.
**    * An EXCLUSIVE or greater lock is held on the database file.
**    * All writing and syncing of journal and database data has finished.
**      If no error occured, all that remains is to finalize the journal to
**      commit the transaction. If an error did occur, the caller will need
**      to rollback the transaction. 
**
**  ERROR:
**
**    The ERROR state is entered when an IO, OOM or disk-full error 
**    occurs at a point in the code that makes it difficult to be sure
**    that the in-memory pager state (cache contents, db size etc.) are
**    consistent with the contents of the file-system.
**
**    For example, if an IO error occurs while performing a rollback, 
**    the contents of the page-cache may be left in an inconsistent state.
**    At this point it would be dangerous to change back to READER state
**    (as usually happens after a rollback). Any subsequent readers might
**    report database corruption (due to the inconsistent cache), and if
**    they upgrade to writers, they may inadvertently corrupt the database
**    file. To avoid this hazard, the pager switches into the ERROR state
**    instead of READER following such an error.
**
**    Once it has entered the ERROR state, any attempt to use the pager
**    to read or write data returns an error. Eventually, once all 
**    outstanding transactions have been abandoned, the pager is able to
**    transition back to OPEN state, discarding the contents of the 
**    page-cache and any other in-memory state at the same time. Everything
**    is reloaded from disk (and, if necessary, hot-journal rollback peformed)
**    when a read-transaction is next opened on the pager (transitioning
**    the pager into READER state). At that point the system has recovered 
**    from the error.
**
**    Specifically, the pager jumps into the ERROR state if:
**
**      1. An error occurs while attempting a rollback. This happens in
**         function sqlite3PagerRollback().
**
**      2. An error occurs while attempting to finalize a journal file
**         following a commit in function sqlite3PagerCommitPhaseTwo().

**
**      3. An error occurs while attempting to write to the journal or
**         database file in function pagerStress() in order to free up
**         memory.
**
**    In other cases, the error is returned to the b-tree layer. The b-tree
**    layer then attempts a rollback operation. If the error condition 
**    persists, the pager enters the ERROR state via condition (1) above.
**
**    Condition (3) is necessary because it can be triggered by a read-only
**    statement executed within a transaction. In this case, if the error
**    code were simply returned to the user, the b-tree layer would not
**    automatically attempt a rollback, as it assumes that an error in a
**    read-only statement cannot leave the pager in an internally inconsistent 
**    state.
**
**    * The Pager.errCode variable is set to something other than SQLITE_OK.
**    * There are one or more outstanding references to pages (after the
**      last reference is dropped the pager should move back to OPEN state).
**    
**
** Notes:
**
**   * A pager is never in WRITER_DBMOD or WRITER_FINISHED state if the
**     connection is open in WAL mode. A WAL connection is always in one
**     of the first four states.
**
**   * Normally, a connection open in exclusive mode is never in PAGER_OPEN
**     state. There are two exceptions: immediately after exclusive-mode has
**     been turned on (and before any read or write transactions are 
**     executed), and when the pager is leaving the "error state".
**
**   * See also: assert_pager_state().
*/
#define PAGER_OPEN                  0



#define PAGER_READER                1
#define PAGER_WRITER_LOCKED         2
#define PAGER_WRITER_CACHEMOD       3
#define PAGER_WRITER_DBMOD          4
#define PAGER_WRITER_FINISHED       5
#define PAGER_ERROR                 6

/*
** The Pager.eLock variable is almost always set to one of the 
** following locking-states, according to the lock currently held on
** the database file: NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
** This variable is kept up to date as locks are taken and released by
** the pagerLockDb() and pagerUnlockDb() wrappers.
**
** If the VFS xLock() or xUnlock() returns an error other than SQLITE_BUSY
** (i.e. one of the SQLITE_IOERR subtypes), it is not clear whether or not
** the operation was successful. In these circumstances pagerLockDb() and
** pagerUnlockDb() take a conservative approach - eLock is always updated
** when unlocking the file, and only updated when locking the file if the
** VFS call is successful. This way, the Pager.eLock variable may be set
** to a less exclusive (lower) value than the lock that is actually held
** at the system level, but it is never set to a more exclusive value.
**
** This is usually safe. If an xUnlock fails or appears to fail, there may 
** be a few redundant xLock() calls or a lock may be held for longer than
** required, but nothing really goes wrong.
**
** The exception is when the database file is unlocked as the pager moves
** from ERROR to OPEN state. At this point there may be a hot-journal file 
** in the file-system that needs to be rolled back (as part of a OPEN->SHARED
** transition, by the same pager or any other). If the call to xUnlock()
** fails at this point and the pager is left holding an EXCLUSIVE lock, this
** can confuse the call to xCheckReservedLock() call made later as part
** of hot-journal detection.
**
** xCheckReservedLock() is defined as returning true "if there is a RESERVED 
** lock held by this process or any others". So xCheckReservedLock may 
** return true because the caller itself is holding an EXCLUSIVE lock (but
** doesn't know it because of a previous error in xUnlock). If this happens
** a hot-journal may be mistaken for a journal being created by an active
** transaction in another process, causing SQLite to read from the database
** without rolling it back.
**
** To work around this, if a call to xUnlock() fails when unlocking the
** database in the ERROR state, Pager.eLock is set to UNKNOWN_LOCK. It
** is only changed back to a real locking state after a successful call
** to xLock(EXCLUSIVE). Also, the code to do the OPEN->SHARED state transition
** omits the check for a hot-journal if Pager.eLock is set to UNKNOWN_LOCK 
** lock. Instead, it assumes a hot-journal exists and obtains an EXCLUSIVE
** lock on the database file before attempting to roll it back. See function
** PagerSharedLock() for more detail.
**
** Pager.eLock may only be set to UNKNOWN_LOCK when the pager is in 
** PAGER_OPEN state.
*/
#define UNKNOWN_LOCK                (EXCLUSIVE_LOCK+1)

/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC1(P,D,N,X,E) \
    if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
................................................................................
  Pgno iSubRec;                /* Index of first record in sub-journal */
#ifndef SQLITE_OMIT_WAL
  u32 aWalData[WAL_SAVEPOINT_NDATA];        /* WAL savepoint context */
#endif
};

/*
** A open page cache is an instance of struct Pager. A description of
** some of the more important member variables follows:
**
** eState
**
**   The current 'state' of the pager object. See the comment and state
**   diagram above for a description of the pager state.
**
** eLock
**
**   For a real on-disk database, the current lock held on the database file -
**   NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
**
**   For a temporary or in-memory database (neither of which require any
**   locks), this variable is always set to EXCLUSIVE_LOCK. Since such
**   databases always have Pager.exclusiveMode==1, this tricks the pager
**   logic into thinking that it already has all the locks it will ever
**   need (and no reason to release them).
**
**   In some (obscure) circumstances, this variable may also be set to
**   UNKNOWN_LOCK. See the comment above the #define of UNKNOWN_LOCK for
**   details.





**
** changeCountDone
**
**   This boolean variable is used to make sure that the change-counter 
**   (the 4-byte header field at byte offset 24 of the database file) is 
**   not updated more often than necessary. 
**
................................................................................
**   The changeCountDone flag is inspected. If it is true, the work of
**   updating the change-counter is omitted for the current transaction.
**
**   This mechanism means that when running in exclusive mode, a connection 
**   need only update the change-counter once, for the first transaction
**   committed.
**


















** setMaster
**
**   When PagerCommitPhaseOne() is called to commit a transaction, it may
**   (or may not) specify a master-journal name to be written into the 
**   journal file before it is synced to disk.
**
**   Whether or not a journal file contains a master-journal pointer affects 
**   the way in which the journal file is finalized after the transaction is 
**   committed or rolled back when running in "journal_mode=PERSIST" mode.
**   If a journal file does not contain a master-journal pointer, it is
**   finalized by overwriting the first journal header with zeroes. If
**   it does contain a master-journal pointer the journal file is finalized 
**   by truncating it to zero bytes, just as if the connection were 
**   running in "journal_mode=truncate" mode.
**
**   Journal files that contain master journal pointers cannot be finalized
**   simply by overwriting the first journal-header with zeroes, as the
**   master journal pointer could interfere with hot-journal rollback of any
**   subsequently interrupted transaction that reuses the journal file.
**
**   The flag is cleared as soon as the journal file is finalized (either
**   by PagerCommitPhaseTwo or PagerRollback). If an IO error prevents the
**   journal file from being successfully finalized, the setMaster flag
**   is cleared anyway (and the pager will move to ERROR state).
**
** doNotSpill, doNotSyncSpill
**
**   These two boolean variables control the behaviour of cache-spills
**   (calls made by the pcache module to the pagerStress() routine to
**   write cached data to the file-system in order to free up memory).




**
**   When doNotSpill is non-zero, writing to the database from pagerStress()
**   is disabled altogether. This is done in a very obscure case that
**   comes up during savepoint rollback that requires the pcache module
**   to allocate a new page to prevent the journal file from being written
**   while it is being traversed by code in pager_playback().
** 
**   If doNotSyncSpill is non-zero, writing to the database from pagerStress()
**   is permitted, but syncing the journal file is not. This flag is set
**   by sqlite3PagerWrite() when the file-system sector-size is larger than
**   the database page-size in order to prevent a journal sync from happening 
**   in between the journalling of two pages on the same sector. 
**
** subjInMemory
**
**   This is a boolean variable. If true, then any required sub-journal
**   is opened as an in-memory journal file. If false, then in-memory
**   sub-journals are only used for in-memory pager files.
**
**   This variable is updated by the upper layer each time a new 
**   write-transaction is opened.
**
** dbSize, dbOrigSize, dbFileSize
**
**   Variable dbSize is set to the number of pages in the database file.
**   It is valid in PAGER_READER and higher states (all states except for
**   OPEN and ERROR). 
**
**   dbSize is set based on the size of the database file, which may be 
**   larger than the size of the database (the value stored at offset
**   28 of the database header by the btree). If the size of the file
**   is not an integer multiple of the page-size, the value stored in
**   dbSize is rounded down (i.e. a 5KB file with 2K page-size has dbSize==2).
**   Except, any file that is greater than 0 bytes in size is considered
**   to have at least one page. (i.e. a 1KB file with 2K page-size leads
**   to dbSize==1).
**
**   During a write-transaction, if pages with page-numbers greater than
**   dbSize are modified in the cache, dbSize is updated accordingly.
**   Similarly, if the database is truncated using PagerTruncateImage(), 
**   dbSize is updated.
**
**   Variables dbOrigSize and dbFileSize are valid in states 
**   PAGER_WRITER_LOCKED and higher. dbOrigSize is a copy of the dbSize
**   variable at the start of the transaction. It is used during rollback,
**   and to determine whether or not pages need to be journalled before
**   being modified.
**
**   Throughout a write-transaction, dbFileSize contains the size of
**   the file on disk in pages. It is set to a copy of dbSize when the
**   write-transaction is first opened, and updated when VFS calls are made
**   to write or truncate the database file on disk. 
**
**   The only reason the dbFileSize variable is required is to suppress 
**   unnecessary calls to xTruncate() after committing a transaction. If, 
**   when a transaction is committed, the dbFileSize variable indicates 
**   that the database file is larger than the database image (Pager.dbSize), 
**   pager_truncate() is called. The pager_truncate() call uses xFilesize()
**   to measure the database file on disk, and then truncates it if required.
**   dbFileSize is not used when rolling back a transaction. In this case
**   pager_truncate() is called unconditionally (which means there may be
**   a call to xFilesize() that is not strictly required). In either case,
**   pager_truncate() may cause the file to become smaller or larger.
**
** dbHintSize
**
**   The dbHintSize variable is used to limit the number of calls made to
**   the VFS xFileControl(FCNTL_SIZE_HINT) method. 
**
**   dbHintSize is set to a copy of the dbSize variable when a
**   write-transaction is opened (at the same time as dbFileSize and
**   dbOrigSize). If the xFileControl(FCNTL_SIZE_HINT) method is called,
**   dbHintSize is increased to the number of pages that correspond to the
**   size-hint passed to the method call. See pager_write_pagelist() for 
**   details.
**
** errCode
**
**   The Pager.errCode variable is only ever used in PAGER_ERROR state. It
**   is set to zero in all other states. In PAGER_ERROR state, Pager.errCode 
**   is always set to SQLITE_FULL, SQLITE_IOERR or one of the SQLITE_IOERR_XXX 
**   sub-codes.
**
**   If Pager.errCode is set to SQLITE_IOERR or one of its subcodes, then
**   this value is immediately returned when ever any sqlite3PagerXXX() method
**   that returns an error code is called. If it is set to SQLITE_FULL,
**   then it is returned whenever any such sqlite3PagerXXX() method except
**   for PagerAcquire() or PagerLookup() is called.
**
**   TODO: Review the SQLITE_FULL/PagerAcquire() exception. Is it a good idea?
**         If so, are there bugs whereby shared-cache clients can see 
**         uncommitted data when the pager is in the ERROR state?
**
*/
struct Pager {
  sqlite3_vfs *pVfs;          /* OS functions to use for IO */
  u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
  u8 journalMode;             /* One of the PAGER_JOURNALMODE_* values */
  u8 useJournal;              /* Use a rollback journal on this file */
  u8 noReadlock;              /* Do not bother to obtain readlocks */
  u8 noSync;                  /* Do not sync the journal if true */
  u8 fullSync;                /* Do extra syncs of the journal for robustness */
  u8 sync_flags;              /* One of SYNC_NORMAL or SYNC_FULL */
  u8 tempFile;                /* zFilename is a temporary file */
  u8 readOnly;                /* True for a read-only database */
................................................................................
  ** operates.
  **
  ** The 'state' variable is described in more detail along with the
  ** descriptions of the values it may take - PAGER_UNLOCK etc. Many of the
  ** other variables in this block are described in the comment directly 
  ** above this class definition.
  */
  u8 eState;                  /* Pager state (OPEN, READER, WRITER_LOCKED..) */
  u8 eLock;                   /* Current lock held on database file */


  u8 changeCountDone;         /* Set after incrementing the change-counter */
  u8 setMaster;               /* True if a m-j name has been written to jrnl */
  u8 doNotSpill;              /* Do not spill the cache when non-zero */
  u8 doNotSyncSpill;          /* Do not do a spill that requires jrnl sync */

  u8 subjInMemory;            /* True to use in-memory sub-journals */
  Pgno dbSize;                /* Number of pages in the database */
  Pgno dbOrigSize;            /* dbSize before the current transaction */
  Pgno dbFileSize;            /* Number of pages in the database file */
  Pgno dbHintSize;            /* Value passed to FCNTL_SIZE_HINT call */
  int errCode;                /* One of several kinds of errors */
  int nRec;                   /* Pages journalled since last j-header written */
  u32 cksumInit;              /* Quasi-random value added to every checksum */
  u32 nSubRec;                /* Number of records written to sub-journal */
  Bitvec *pInJournal;         /* One bit for each page in the database file */
  sqlite3_file *fd;           /* File descriptor for database */
  sqlite3_file *jfd;          /* File descriptor for main journal */
................................................................................
#endif

/*
** The maximum legal page number is (2^31 - 1).
*/
#define PAGER_MAX_PGNO 2147483647

/*
** The argument to this macro is a file descriptor (type sqlite3_file*).
** Return 0 if it is not open, or non-zero (but not 1) if it is.
**
** This is so that expressions can be written as:
**
**   if( isOpen(pPager->jfd) ){ ...
**
** instead of
**
**   if( pPager->jfd->pMethods ){ ...
*/
#define isOpen(pFd) ((pFd)->pMethods)

/*
** Return true if this pager uses a write-ahead log instead of the usual
** rollback journal. Otherwise false.
*/
#ifndef SQLITE_OMIT_WAL
static int pagerUseWal(Pager *pPager){
  return (pPager->pWal!=0);
}
#else
# define pagerUseWal(x) 0
# define pagerRollbackWal(x) 0
# define pagerWalFrames(v,w,x,y,z) 0
# define pagerOpenWalIfPresent(z) SQLITE_OK
# define pagerBeginReadTransaction(z) SQLITE_OK
#endif

#ifndef NDEBUG 
/*
** Usage:
**
**   assert( assert_pager_state(pPager) );
**
** This function runs many asserts to try to find inconsistencies in
** the internal state of the Pager object.
*/
static int assert_pager_state(Pager *p){
  Pager *pPager = p;



  /* State must be valid. */
  assert( p->eState==PAGER_OPEN
       || p->eState==PAGER_READER
       || p->eState==PAGER_WRITER_LOCKED
       || p->eState==PAGER_WRITER_CACHEMOD
       || p->eState==PAGER_WRITER_DBMOD
       || p->eState==PAGER_WRITER_FINISHED
       || p->eState==PAGER_ERROR
  );

  /* Regardless of the current state, a temp-file connection always behaves
  ** as if it has an exclusive lock on the database file. It never updates
  ** the change-counter field, so the changeCountDone flag is always set.
  */
  assert( p->tempFile==0 || p->eLock==EXCLUSIVE_LOCK );
  assert( p->tempFile==0 || pPager->changeCountDone );

  /* If the useJournal flag is clear, the journal-mode must be "OFF". 
  ** And if the journal-mode is "OFF", the journal file must not be open.
  */
  assert( p->journalMode==PAGER_JOURNALMODE_OFF || p->useJournal );
  assert( p->journalMode!=PAGER_JOURNALMODE_OFF || !isOpen(p->jfd) );

  /* Check that MEMDB implies noSync. */
  assert( !MEMDB || p->noSync );

  /* If changeCountDone is set, a RESERVED lock or greater must be held
  ** on the file.
  */
  assert( pPager->changeCountDone==0 || pPager->eLock>=RESERVED_LOCK );
  assert( p->eLock!=PENDING_LOCK );

  switch( p->eState ){
    case PAGER_OPEN:
      assert( !MEMDB );
      assert( pPager->errCode==SQLITE_OK );
      assert( sqlite3PcacheRefCount(pPager->pPCache)==0 || pPager->tempFile );
      break;

    case PAGER_READER:
      assert( pPager->errCode==SQLITE_OK );
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( p->eLock>=SHARED_LOCK || p->noReadlock );
      break;

    case PAGER_WRITER_LOCKED:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        assert( p->eLock>=RESERVED_LOCK );
      }
      assert( pPager->dbSize==pPager->dbOrigSize );
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->dbOrigSize==pPager->dbHintSize );
      assert( pPager->setMaster==0 );
      break;

    case PAGER_WRITER_CACHEMOD:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        /* It is possible that if journal_mode=wal here that neither the
        ** journal file nor the WAL file are open. This happens during
        ** a rollback transaction that switches from journal_mode=off
        ** to journal_mode=wal.
        */
        assert( p->eLock>=RESERVED_LOCK );
        assert( isOpen(p->jfd) 
             || p->journalMode==PAGER_JOURNALMODE_OFF 
             || p->journalMode==PAGER_JOURNALMODE_WAL 
        );
      }
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->dbOrigSize==pPager->dbHintSize );
      break;

    case PAGER_WRITER_DBMOD:
      assert( p->eLock==EXCLUSIVE_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( p->eLock>=EXCLUSIVE_LOCK );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      assert( pPager->dbOrigSize<=pPager->dbHintSize );
      break;

    case PAGER_WRITER_FINISHED:
      assert( p->eLock==EXCLUSIVE_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      break;

    case PAGER_ERROR:
      /* There must be at least one outstanding reference to the pager if
      ** in ERROR state. Otherwise the pager should have already dropped
      ** back to OPEN state.
      */
      assert( pPager->errCode!=SQLITE_OK );
      assert( sqlite3PcacheRefCount(pPager->pPCache)>0 );
      break;
  }

  return 1;
}

/*
** Return a pointer to a human readable string in a static buffer
** containing the state of the Pager object passed as an argument. This
** is intended to be used within debuggers. For example, as an alternative
** to "print *pPager" in gdb:
**
** (gdb) printf "%s", print_pager_state(pPager)
*/
static char *print_pager_state(Pager *p){
  static char zRet[1024];

  sqlite3_snprintf(1024, zRet,
      "Filename:      %s\n"
      "State:         %s errCode=%d\n"
      "Lock:          %s\n"
      "Locking mode:  locking_mode=%s\n"
      "Journal mode:  journal_mode=%s\n"
      "Backing store: tempFile=%d memDb=%d useJournal=%d\n"
      "Journal:       journalOff=%lld journalHdr=%lld\n"
      "Size:          dbsize=%d dbOrigSize=%d dbFileSize=%d\n"
      , p->zFilename
      , p->eState==PAGER_OPEN            ? "OPEN" :
        p->eState==PAGER_READER          ? "READER" :
        p->eState==PAGER_WRITER_LOCKED   ? "WRITER_LOCKED" :
        p->eState==PAGER_WRITER_CACHEMOD ? "WRITER_CACHEMOD" :
        p->eState==PAGER_WRITER_DBMOD    ? "WRITER_DBMOD" :
        p->eState==PAGER_WRITER_FINISHED ? "WRITER_FINISHED" :
        p->eState==PAGER_ERROR           ? "ERROR" : "?error?"
      , (int)p->errCode
      , p->eLock==NO_LOCK         ? "NO_LOCK" :
        p->eLock==RESERVED_LOCK   ? "RESERVED" :
        p->eLock==EXCLUSIVE_LOCK  ? "EXCLUSIVE" :
        p->eLock==SHARED_LOCK     ? "SHARED" :
        p->eLock==UNKNOWN_LOCK    ? "UNKNOWN" : "?error?"
      , p->exclusiveMode ? "exclusive" : "normal"
      , p->journalMode==PAGER_JOURNALMODE_MEMORY   ? "memory" :
        p->journalMode==PAGER_JOURNALMODE_OFF      ? "off" :
        p->journalMode==PAGER_JOURNALMODE_DELETE   ? "delete" :
        p->journalMode==PAGER_JOURNALMODE_PERSIST  ? "persist" :
        p->journalMode==PAGER_JOURNALMODE_TRUNCATE ? "truncate" :
        p->journalMode==PAGER_JOURNALMODE_WAL      ? "wal" : "?error?"
      , (int)p->tempFile, (int)p->memDb, (int)p->useJournal
      , p->journalOff, p->journalHdr
      , (int)p->dbSize, (int)p->dbOrigSize, (int)p->dbFileSize
  );

  return zRet;
}
#endif

/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
................................................................................
  return rc;
}

/*
** Write a 32-bit integer into a string buffer in big-endian byte order.
*/
#define put32bits(A,B)  sqlite3Put4byte((u8*)A,B)


/*
** Write a 32-bit integer into the given file descriptor.  Return SQLITE_OK
** on success or an error code is something goes wrong.
*/
static int write32bits(sqlite3_file *fd, i64 offset, u32 val){
  char ac[4];
  put32bits(ac, val);
  return sqlite3OsWrite(fd, ac, 4, offset);
}

/*
** Unlock the database file to level eLock, which must be either NO_LOCK
** or SHARED_LOCK. Regardless of whether or not the call to xUnlock()
** succeeds, set the Pager.eLock variable to match the (attempted) new lock.

**
** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is
** called, do not modify it. See the comment above the #define of 
** UNKNOWN_LOCK for an explanation of this.



*/
static int pagerUnlockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;

  assert( !pPager->exclusiveMode );
  assert( eLock==NO_LOCK || eLock==SHARED_LOCK );
  assert( eLock!=NO_LOCK || pagerUseWal(pPager)==0 );
  if( isOpen(pPager->fd) ){
    assert( pPager->eLock>=eLock );
    rc = sqlite3OsUnlock(pPager->fd, eLock);
    if( pPager->eLock!=UNKNOWN_LOCK ){
      pPager->eLock = eLock;
    }
    IOTRACE(("UNLOCK %p %d\n", pPager, eLock))
  }
  return rc;
}

/*

** Lock the database file to level eLock, which must be either SHARED_LOCK,
** RESERVED_LOCK or EXCLUSIVE_LOCK. If the caller is successful, set the
** Pager.eLock variable to the new locking state. 
**
** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is 
** called, do not modify it unless the new locking state is EXCLUSIVE_LOCK. 
** See the comment above the #define of UNKNOWN_LOCK for an explanation 
** of this.
*/


static int pagerLockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;


  assert( eLock==SHARED_LOCK || eLock==RESERVED_LOCK || eLock==EXCLUSIVE_LOCK );
  if( pPager->eLock<eLock || pPager->eLock==UNKNOWN_LOCK ){
    rc = sqlite3OsLock(pPager->fd, eLock);
    if( rc==SQLITE_OK && (pPager->eLock!=UNKNOWN_LOCK||eLock==EXCLUSIVE_LOCK) ){
      pPager->eLock = eLock;
      IOTRACE(("LOCK %p %d\n", pPager, eLock))
    }
  }
  return rc;
}

/*
** This function determines whether or not the atomic-write optimization
** can be used with this pager. The optimization can be used if:
**
**  (a) the value returned by OsDeviceCharacteristics() indicates that
................................................................................
  **   * When the pager is in no-sync mode. Corruption can follow a
  **     power failure in this case anyway.
  **
  **   * When the SQLITE_IOCAP_SAFE_APPEND flag is set. This guarantees
  **     that garbage data is never appended to the journal file.
  */
  assert( isOpen(pPager->fd) || pPager->noSync );
  if( pPager->noSync || (pPager->journalMode==PAGER_JOURNALMODE_MEMORY)
   || (sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND) 
  ){
    memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
    put32bits(&zHeader[sizeof(aJournalMagic)], 0xffffffff);
  }else{
    memset(zHeader, 0, sizeof(aJournalMagic)+4);
  }
................................................................................
  int rc;                          /* Return code */
  int nMaster;                     /* Length of string zMaster */
  i64 iHdrOff;                     /* Offset of header in journal file */
  i64 jrnlSize;                    /* Size of journal file on disk */
  u32 cksum = 0;                   /* Checksum of string zMaster */

  assert( pPager->setMaster==0 );
  assert( !pagerUseWal(pPager) );

  if( !zMaster 
   || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
   || pPager->journalMode==PAGER_JOURNALMODE_OFF 
  ){
    return SQLITE_OK;
  }
  pPager->setMaster = 1;
................................................................................
   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster, nMaster)))
   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster+4, cksum)))
   || (0 != (rc = sqlite3OsWrite(pPager->jfd, aJournalMagic, 8, iHdrOff+4+nMaster+8)))
  ){
    return rc;
  }
  pPager->journalOff += (nMaster+20);


  /* If the pager is in peristent-journal mode, then the physical 
  ** journal-file may extend past the end of the master-journal name
  ** and 8 bytes of magic data just written to the file. This is 
  ** dangerous because the code to rollback a hot-journal file
  ** will not be able to find the master-journal name to determine 
  ** whether or not the journal is hot. 
................................................................................
  ** fail, since no attempt to allocate dynamic memory will be made.
  */
  (void)sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &p);
  return p;
}

/*
** Discard the entire contents of the in-memory page-cache.



*/
static void pager_reset(Pager *pPager){

  sqlite3BackupRestart(pPager->pBackup);
  sqlite3PcacheClear(pPager->pPCache);


}

/*
** Free all structures in the Pager.aSavepoint[] array and set both
** Pager.aSavepoint and Pager.nSavepoint to zero. Close the sub-journal
** if it is open and the pager is not in exclusive mode.
*/
................................................................................
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}

/*
** This function is a no-op if the pager is in exclusive mode and not
** in the ERROR state. Otherwise, it switches the pager to PAGER_OPEN
** state.
**
** If the pager is not in exclusive-access mode, the database file is
** completely unlocked. If the file is unlocked and the file-system does
** not exhibit the UNDELETABLE_WHEN_OPEN property, the journal file is
** closed (if it is open).
**
** If the pager is in ERROR state when this function is called, the 
** contents of the pager cache are discarded before switching back to 
** the OPEN state. Regardless of whether the pager is in exclusive-mode
** or not, any journal file left in the file-system will be treated
** as a hot-journal and rolled back the next time a read-transaction
** is opened (by this or by any other connection).
*/
static void pager_unlock(Pager *pPager){

  assert( pPager->eState==PAGER_READER 
       || pPager->eState==PAGER_OPEN 
       || pPager->eState==PAGER_ERROR 
  );

  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  releaseAllSavepoints(pPager);

  if( pagerUseWal(pPager) ){
    assert( !isOpen(pPager->jfd) );
    sqlite3WalEndReadTransaction(pPager->pWal);
    pPager->eState = PAGER_OPEN;
  }else if( !pPager->exclusiveMode ){
    int rc;                       /* Error code returned by pagerUnlockDb() */
    int iDc = isOpen(pPager->fd)?sqlite3OsDeviceCharacteristics(pPager->fd):0;

    /* If the operating system support deletion of open files, then
    ** close the journal file when dropping the database lock.  Otherwise
    ** another connection with journal_mode=delete might delete the file
    ** out from under us.
    */
................................................................................
    assert( (PAGER_JOURNALMODE_PERSIST  & 5)==1 );
    if( 0==(iDc & SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN)
     || 1!=(pPager->journalMode & 5)
    ){
      sqlite3OsClose(pPager->jfd);
    }

    /* If the pager is in the ERROR state and the call to unlock the database
    ** file fails, set the current lock to UNKNOWN_LOCK. See the comment
    ** above the #define for UNKNOWN_LOCK for an explanation of why this
    ** is necessary.
    */
    rc = pagerUnlockDb(pPager, NO_LOCK);
    if( rc!=SQLITE_OK && pPager->eState==PAGER_ERROR ){
      pPager->eLock = UNKNOWN_LOCK;
    }

    /* The pager state may be changed from PAGER_ERROR to PAGER_OPEN here
    ** without clearing the error code. This is intentional - the error
    ** code is cleared and the cache reset in the block below.
    */
    assert( pPager->errCode || pPager->eState!=PAGER_ERROR );
    pPager->changeCountDone = 0;
    pPager->eState = PAGER_OPEN;
  }

  /* If Pager.errCode is set, the contents of the pager cache cannot be
  ** trusted. Now that there are no outstanding references to the pager,
  ** it can safely move back to PAGER_OPEN state. This happens in both
  ** normal and exclusive-locking mode.
  */
  if( pPager->errCode && !MEMDB ){
    pager_reset(pPager);
    pPager->changeCountDone = pPager->tempFile;
    pPager->eState = PAGER_OPEN;
    pPager->errCode = SQLITE_OK;
  }

  pPager->journalOff = 0;
  pPager->journalHdr = 0;
  pPager->setMaster = 0;
}

/*
** This function is called whenever an IOERR or FULL error that requires
** the pager to transition into the ERROR state may ahve occurred.
** The first argument is a pointer to the pager structure, the second 
** the error-code about to be returned by a pager API function. The 
** value returned is a copy of the second argument to this function. 
**
** If the second argument is SQLITE_FULL, SQLITE_IOERR or one of the
** IOERR sub-codes, the pager enters the ERROR state and the error code
** is stored in Pager.errCode. While the pager remains in the ERROR state,
** all major API calls on the Pager will immediately return Pager.errCode.
** Except, if the error-code is SQLITE_FULL, calls to PagerLookup() and
** PagerAcquire are handled as if the pager were in PAGER_READER state.
**
** The ERROR state indicates that the contents of the pager-cache 

** cannot be trusted. This state can be cleared by completely discarding 
** the contents of the pager-cache. If a transaction was active when
** the persistent error occurred, then the rollback journal may need
** to be replayed to restore the contents of the database file (as if
** it were a hot-journal).
*/
static int pager_error(Pager *pPager, int rc){
................................................................................
  assert(
       pPager->errCode==SQLITE_FULL ||
       pPager->errCode==SQLITE_OK ||
       (pPager->errCode & 0xff)==SQLITE_IOERR
  );
  if( rc2==SQLITE_FULL || rc2==SQLITE_IOERR ){
    pPager->errCode = rc;
    pPager->eState = PAGER_ERROR;
  }
  return rc;
}



























/*
** This routine ends a transaction. A transaction is usually ended by 
** either a COMMIT or a ROLLBACK operation. This routine may be called 
** after rollback of a hot-journal, or if an error occurs while opening
** the journal file or writing the very first journal-header of a
** database transaction.
** 
** This routine is never called in PAGER_ERROR state. If it is called
** in PAGER_NONE or PAGER_SHARED state and the lock held is less
** exclusive than a RESERVED lock, it is a no-op.
**
** Otherwise, any active savepoints are released.
**
** If the journal file is open, then it is "finalized". Once a journal 
** file has been finalized it is not possible to use it to roll back a 
** transaction. Nor will it be considered to be a hot-journal by this
** or any other database connection. Exactly how a journal is finalized
................................................................................
**     The journal file is closed and deleted using sqlite3OsDelete().
**
**     If the pager is running in exclusive mode, this method of finalizing
**     the journal file is never used. Instead, if the journalMode is
**     DELETE and the pager is in exclusive mode, the method described under
**     journalMode==PERSIST is used instead.
**
** After the journal is finalized, the pager moves to PAGER_READER state.
** If running in non-exclusive rollback mode, the lock on the file is 
** downgraded to a SHARED_LOCK.




**
** SQLITE_OK is returned if no error occurs. If an error occurs during
** any of the IO operations to finalize the journal file or unlock the
** database then the IO error code is returned to the user. If the 
** operation to finalize the journal file fails, then the code still
** tries to unlock the database file if not in exclusive mode. If the
** unlock operation fails as well, then the first error code related
................................................................................
** to the first error encountered (the journal finalization one) is
** returned.
*/
static int pager_end_transaction(Pager *pPager, int hasMaster){
  int rc = SQLITE_OK;      /* Error code from journal finalization operation */
  int rc2 = SQLITE_OK;     /* Error code from db file unlock operation */

  /* Do nothing if the pager does not have an open write transaction
  ** or at least a RESERVED lock. This function may be called when there
  ** is no write-transaction active but a RESERVED or greater lock is
  ** held under two circumstances:
  **
  **   1. After a successful hot-journal rollback, it is called with
  **      eState==PAGER_NONE and eLock==EXCLUSIVE_LOCK.
  **
  **   2. If a connection with locking_mode=exclusive holding an EXCLUSIVE 
  **      lock switches back to locking_mode=normal and then executes a
  **      read-transaction, this function is called with eState==PAGER_READER 
  **      and eLock==EXCLUSIVE_LOCK when the read-transaction is closed.
  */
  assert( assert_pager_state(pPager) );
  assert( pPager->eState!=PAGER_ERROR );
  if( pPager->eState<PAGER_WRITER_LOCKED && pPager->eLock<RESERVED_LOCK ){
    return SQLITE_OK;
  }


  releaseAllSavepoints(pPager);
  assert( isOpen(pPager->jfd) || pPager->pInJournal==0 );
  if( isOpen(pPager->jfd) ){
    assert( !pagerUseWal(pPager) );

    /* Finalize the journal file. */
    if( sqlite3IsMemJournal(pPager->jfd) ){
      assert( pPager->journalMode==PAGER_JOURNALMODE_MEMORY );
................................................................................
    }else if( pPager->journalMode==PAGER_JOURNALMODE_TRUNCATE ){
      if( pPager->journalOff==0 ){
        rc = SQLITE_OK;
      }else{
        rc = sqlite3OsTruncate(pPager->jfd, 0);
      }
      pPager->journalOff = 0;

    }else if( pPager->journalMode==PAGER_JOURNALMODE_PERSIST
      || (pPager->exclusiveMode && pPager->journalMode!=PAGER_JOURNALMODE_WAL)
    ){
      rc = zeroJournalHdr(pPager, hasMaster);

      pPager->journalOff = 0;

    }else{
      /* This branch may be executed with Pager.journalMode==MEMORY if
      ** a hot-journal was just rolled back. In this case the journal
      ** file should be closed and deleted. If this connection writes to
      ** the database file, it will do so using an in-memory journal. 
      */
      assert( pPager->journalMode==PAGER_JOURNALMODE_DELETE 
................................................................................
    sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
#endif
  }
  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  pPager->nRec = 0;
  sqlite3PcacheCleanAll(pPager->pPCache);
  sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);

  if( pagerUseWal(pPager) ){

    /* Drop the WAL write-lock, if any. Also, if the connection was in 


    ** locking_mode=exclusive mode but is no longer, drop the EXCLUSIVE 
    ** lock held on the database file.
    */


    rc2 = sqlite3WalEndWriteTransaction(pPager->pWal);
    assert( rc2==SQLITE_OK );
  }
  if( !pPager->exclusiveMode 
   && (!pagerUseWal(pPager) || sqlite3WalExclusiveMode(pPager->pWal, 0))
  ){
    rc2 = pagerUnlockDb(pPager, SHARED_LOCK);

    pPager->changeCountDone = 0;


  }
  pPager->eState = PAGER_READER;
  pPager->setMaster = 0;



  return (rc==SQLITE_OK?rc2:rc);
}

/*
** Execute a rollback if a transaction is active and unlock the 
** database file. 

**
** If the pager has already entered the ERROR state, do not attempt 
** the rollback at this time. Instead, pager_unlock() is called. The
** call to pager_unlock() will discard all in-memory pages, unlock
** the database file and move the pager back to OPEN state. If this 
** means that there is a hot-journal left in the file-system, the next 
** connection to obtain a shared lock on the pager (which may be this one) 
** will roll it back.
**
** If the pager has not already entered the ERROR state, but an IO or
** malloc error occurs during a rollback, then this will itself cause 
** the pager to enter the ERROR state. Which will be cleared by the
** call to pager_unlock(), as described above.
*/
static void pagerUnlockAndRollback(Pager *pPager){
  if( pPager->eState!=PAGER_ERROR && pPager->eState!=PAGER_OPEN ){
    assert( assert_pager_state(pPager) );
    if( pPager->eState>=PAGER_WRITER_LOCKED ){
      sqlite3BeginBenignMalloc();
      sqlite3PagerRollback(pPager);
      sqlite3EndBenignMalloc();
    }else if( !pPager->exclusiveMode ){
      assert( pPager->eState==PAGER_READER );
      pager_end_transaction(pPager, 0);
    }
  }

  pager_unlock(pPager);
}

/*
** Parameter aData must point to a buffer of pPager->pageSize bytes
** of data. Compute and return a checksum based ont the contents of the 
** page of data and the current value of pPager->cksumInit.
**
** This is not a real checksum. It is really just the sum of the 
................................................................................

/*
** Read a single page from either the journal file (if isMainJrnl==1) or
** from the sub-journal (if isMainJrnl==0) and playback that page.
** The page begins at offset *pOffset into the file. The *pOffset
** value is increased to the start of the next page in the journal.
**
** The main rollback journal uses checksums - the statement journal does 
** not.

**
** If the page number of the page record read from the (sub-)journal file
** is greater than the current value of Pager.dbSize, then playback is
** skipped and SQLITE_OK is returned.
**
** If pDone is not NULL, then it is a record of pages that have already
** been played back.  If the page at *pOffset has already been played back
................................................................................
  assert( (isSavepnt&~1)==0 );       /* isSavepnt is 0 or 1 */
  assert( isMainJrnl || pDone );     /* pDone always used on sub-journals */
  assert( isSavepnt || pDone==0 );   /* pDone never used on non-savepoint */

  aData = pPager->pTmpSpace;
  assert( aData );         /* Temp storage must have already been allocated */
  assert( pagerUseWal(pPager)==0 || (!isMainJrnl && isSavepnt) );

  /* Either the state is greater than PAGER_WRITER_CACHEMOD (a transaction 
  ** or savepoint rollback done at the request of the caller) or this is
  ** a hot-journal rollback. If it is a hot-journal rollback, the pager
  ** is in state OPEN and holds an EXCLUSIVE lock. Hot-journal rollback
  ** only reads from the main journal, not the sub-journal.
  */
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD
       || (pPager->eState==PAGER_OPEN && pPager->eLock==EXCLUSIVE_LOCK)
  );
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD || isMainJrnl );

  /* Read the page number and page data from the journal or sub-journal
  ** file. Return an error code to the caller if an IO error occurs.
  */
  jfd = isMainJrnl ? pPager->jfd : pPager->sjfd;
  rc = read32bits(jfd, *pOffset, &pgno);
  if( rc!=SQLITE_OK ) return rc;
................................................................................

  /* If this page has already been played by before during the current
  ** rollback, then don't bother to play it back again.
  */
  if( pDone && (rc = sqlite3BitvecSet(pDone, pgno))!=SQLITE_OK ){
    return rc;
  }


  /* When playing back page 1, restore the nReserve setting
  */
  if( pgno==1 && pPager->nReserve!=((u8*)aData)[20] ){
    pPager->nReserve = ((u8*)aData)[20];
    pagerReportSize(pPager);
  }

  /* If the pager is in CACHEMOD state, then there must be a copy of this
  ** page in the pager cache. In this case just update the pager cache,
  ** not the database file. The page is left marked dirty in this case.
  **
  ** An exception to the above rule: If the database is in no-sync mode
  ** and a page is moved during an incremental vacuum then the page may
  ** not be in the pager cache. Later: if a malloc() or IO error occurs
  ** during a Movepage() call, then the page may not be in the cache
  ** either. So the condition described in the above paragraph is not
  ** assert()able.
  **
  ** If in WRITER_DBMOD, WRITER_FINISHED or OPEN state, then we update the
  ** pager cache if it exists and the main file. The page is then marked 
  ** not dirty. Since this code is only executed in PAGER_OPEN state for
  ** a hot-journal rollback, it is guaranteed that the page-cache is empty
  ** if the pager is in OPEN state.
  **
  ** Ticket #1171:  The statement journal might contain page content that is
  ** different from the page content at the start of the transaction.
  ** This occurs when a page is changed prior to the start of a statement
  ** then changed again within the statement.  When rolling back such a
  ** statement we must not write to the original database unless we know
  ** for certain that original page contents are synced into the main rollback
................................................................................
  */
  if( pagerUseWal(pPager) ){
    pPg = 0;
  }else{
    pPg = pager_lookup(pPager, pgno);
  }
  assert( pPg || !MEMDB );
  assert( pPager->eState!=PAGER_OPEN || pPg==0 );
  PAGERTRACE(("PLAYBACK %d page %d hash(%08x) %s\n",
           PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, (u8*)aData),
           (isMainJrnl?"main-journal":"sub-journal")
  ));
  if( isMainJrnl ){
    isSynced = pPager->noSync || (*pOffset <= pPager->journalHdr);
  }else{
    isSynced = (pPg==0 || 0==(pPg->flags & PGHDR_NEED_SYNC));
  }
  if( (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN)
   && isOpen(pPager->fd)
   && isSynced
  ){
    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
    testcase( !isSavepnt && pPg!=0 && (pPg->flags&PGHDR_NEED_SYNC)!=0 );
    assert( !pagerUseWal(pPager) );
    rc = sqlite3OsWrite(pPager->fd, (u8*)aData, pPager->pageSize, ofst);
................................................................................


/*
** This function is used to change the actual size of the database 
** file in the file-system. This only happens when committing a transaction,
** or rolling back a transaction (including rolling back a hot-journal).
**
** If the main database file is not open, or the pager is not in either
** DBMOD or OPEN state, this function is a no-op. Otherwise, the size 
** of the file is changed to nPage pages (nPage*pPager->pageSize bytes). 
** If the file on disk is currently larger than nPage pages, then use the VFS
** xTruncate() method to truncate it.
**
** Or, it might might be the case that the file on disk is smaller than 
** nPage pages. Some operating system implementations can get confused if 
** you try to truncate a file to some size that is larger than it 
** currently is, so detect this case and write a single zero byte to 
** the end of the new file instead.
**
** If successful, return SQLITE_OK. If an IO error occurs while modifying
** the database file, return the error code to the caller.
*/
static int pager_truncate(Pager *pPager, Pgno nPage){
  int rc = SQLITE_OK;
  assert( pPager->eState!=PAGER_ERROR );
  assert( pPager->eState!=PAGER_READER );
  
  if( isOpen(pPager->fd) 
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN) 
  ){
    i64 currentSize, newSize;
    assert( pPager->eLock==EXCLUSIVE_LOCK );
    /* TODO: Is it safe to use Pager.dbFileSize here? */
    rc = sqlite3OsFileSize(pPager->fd, &currentSize);
    newSize = pPager->pageSize*(i64)nPage;
    if( rc==SQLITE_OK && currentSize!=newSize ){
      if( currentSize>newSize ){
        rc = sqlite3OsTruncate(pPager->fd, newSize);
      }else{
................................................................................
  u32 nRec;                /* Number of Records in the journal */
  u32 u;                   /* Unsigned loop counter */
  Pgno mxPg = 0;           /* Size of the original file in pages */
  int rc;                  /* Result code of a subroutine */
  int res = 1;             /* Value returned by sqlite3OsAccess() */
  char *zMaster = 0;       /* Name of master journal file if any */
  int needPagerReset;      /* True to reset page prior to first page rollback */

  if( !isOpen(pPager->jfd) ){
    return SQLITE_OK;
  }

  /* Figure out how many records are in the journal.  Abort early if
  ** the journal is empty.
  */

  rc = sqlite3OsFileSize(pPager->jfd, &szJ);
  if( rc!=SQLITE_OK || szJ==0 ){
    goto end_playback;
  }

  /* Read the master journal name from the journal, if it is present.
  ** If a master journal file name is specified, but the file is not
................................................................................
  pPager->changeCountDone = pPager->tempFile;

  if( rc==SQLITE_OK ){
    zMaster = pPager->pTmpSpace;
    rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
    testcase( rc!=SQLITE_OK );
  }
  if( rc==SQLITE_OK && !pPager->noSync 
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN)


  ){
    rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
  }
  if( rc==SQLITE_OK ){
    rc = pager_end_transaction(pPager, zMaster[0]!='\0');
    testcase( rc!=SQLITE_OK );
  }
  if( rc==SQLITE_OK && zMaster[0] && res ){
................................................................................
static int readDbPage(PgHdr *pPg){
  Pager *pPager = pPg->pPager; /* Pager object associated with page pPg */
  Pgno pgno = pPg->pgno;       /* Page number to read */
  int rc = SQLITE_OK;          /* Return code */
  int isInWal = 0;             /* True if page is in log file */
  int pgsz = pPager->pageSize; /* Number of bytes to read */

  assert( pPager->eState>=PAGER_READER && !MEMDB );
  assert( isOpen(pPager->fd) );

  if( NEVER(!isOpen(pPager->fd)) ){
    assert( pPager->tempFile );
    memset(pPg->pData, 0, pPager->pageSize);
    return SQLITE_OK;
  }
................................................................................
** other writers or checkpointers.
*/
static int pagerBeginReadTransaction(Pager *pPager){
  int rc;                         /* Return code */
  int changed = 0;                /* True if cache must be reset */

  assert( pagerUseWal(pPager) );
  assert( pPager->eState==PAGER_OPEN || pPager->eState==PAGER_READER );

  /* sqlite3WalEndReadTransaction() was not called for the previous
  ** transaction in locking_mode=EXCLUSIVE.  So call it now.  If we
  ** are in locking_mode=NORMAL and EndRead() was previously called,
  ** the duplicate call is harmless.
  */
  sqlite3WalEndReadTransaction(pPager->pWal);

  rc = sqlite3WalBeginReadTransaction(pPager->pWal, &changed);
  if( rc==SQLITE_OK && changed ){


    pager_reset(pPager);

  }



  return rc;
}

/*
** This function is called as part of the transition from PAGER_OPEN
** to PAGER_READER state to determine the size of the database file
** in pages (assuming the page size currently stored in Pager.pageSize).
**
** If no error occurs, SQLITE_OK is returned and the size of the database
** in pages is stored in *pnPage. Otherwise, an error code (perhaps
** SQLITE_IOERR_FSTAT) is returned and *pnPage is left unmodified.
*/
static int pagerPagecount(Pager *pPager, Pgno *pnPage){
  Pgno nPage;                     /* Value to return via *pnPage */

  /* Query the WAL sub-system for the database size. The WalDbsize()
  ** function returns zero if the WAL is not open (i.e. Pager.pWal==0), or
  ** if the database size is not available. The database size is not
  ** available from the WAL sub-system if the log file is empty or
  ** contains no valid committed transactions.
  */
  assert( pPager->eState==PAGER_OPEN );
  assert( pPager->eLock>=SHARED_LOCK || pPager->noReadlock );
  nPage = sqlite3WalDbsize(pPager->pWal);

  /* If the database size was not available from the WAL sub-system,
  ** determine it based on the size of the database file. If the size
  ** of the database file is not an integer multiple of the page-size,
  ** round down to the nearest page. Except, any file larger than 0
  ** bytes in size is considered to contain at least one page.
  */
  if( nPage==0 ){
    i64 n = 0;                    /* Size of db file in bytes */
    assert( isOpen(pPager->fd) || pPager->tempFile );
    if( isOpen(pPager->fd) ){
      int rc = sqlite3OsFileSize(pPager->fd, &n);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
    nPage = (Pgno)(n / pPager->pageSize);
    if( nPage==0 && n>0 ){
      nPage = 1;
    }
  }

  /* If the current number of pages in the file is greater than the
  ** configured maximum pager number, increase the allowed limit so
  ** that the file can be read.
  */
  if( nPage>pPager->mxPgno ){
    pPager->mxPgno = (Pgno)nPage;
  }

  *pnPage = nPage;
  return SQLITE_OK;
}


/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists if the database is not empy, or verify that the *-wal file does
** not exist (by deleting it) if the database file is empty.
**
** If the database is not empty and the *-wal file exists, open the pager
** in WAL mode.  If the database is empty or if no *-wal file exists and
** if no error occurs, make sure Pager.journalMode is not set to
** PAGER_JOURNALMODE_WAL.
**
** Return SQLITE_OK or an error code.
**


** The caller must hold a SHARED lock on the database file to call this
** function. Because an EXCLUSIVE lock on the db file is required to delete 
** a WAL on a none-empty database, this ensures there is no race condition 
** between the xAccess() below and an xDelete() being executed by some 
** other connection.
*/
static int pagerOpenWalIfPresent(Pager *pPager){
  int rc = SQLITE_OK;
  assert( pPager->eState==PAGER_OPEN );
  assert( pPager->eLock>=SHARED_LOCK || pPager->noReadlock );

  if( !pPager->tempFile ){
    int isWal;                    /* True if WAL file exists */
    Pgno nPage;                   /* Size of the database file */


    rc = pagerPagecount(pPager, &nPage);
    if( rc ) return rc;
    if( nPage==0 ){
      rc = sqlite3OsDelete(pPager->pVfs, pPager->zWal, 0);
      isWal = 0;
    }else{
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &isWal
      );
    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        testcase( sqlite3PcachePagecount(pPager->pPCache)==0 );
        rc = sqlite3PagerOpenWal(pPager, 0);



      }else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
        pPager->journalMode = PAGER_JOURNALMODE_DELETE;
      }
    }
  }
  return rc;
}
................................................................................
*/
static int pagerPlaybackSavepoint(Pager *pPager, PagerSavepoint *pSavepoint){
  i64 szJ;                 /* Effective size of the main journal */
  i64 iHdrOff;             /* End of first segment of main-journal records */
  int rc = SQLITE_OK;      /* Return code */
  Bitvec *pDone = 0;       /* Bitvec to ensure pages played back only once */

  assert( pPager->eState!=PAGER_ERROR );
  assert( pPager->eState>=PAGER_WRITER_LOCKED );

  /* Allocate a bitvec to use to store the set of pages rolled back */
  if( pSavepoint ){
    pDone = sqlite3BitvecCreate(pSavepoint->nOrig);
    if( !pDone ){
      return SQLITE_NOMEM;
    }
................................................................................
** and FULL=3.
*/
#ifndef SQLITE_OMIT_PAGER_PRAGMAS
void sqlite3PagerSetSafetyLevel(Pager *pPager, int level, int bFullFsync){
  pPager->noSync =  (level==1 || pPager->tempFile) ?1:0;
  pPager->fullSync = (level==3 && !pPager->tempFile) ?1:0;
  pPager->sync_flags = (bFullFsync?SQLITE_SYNC_FULL:SQLITE_SYNC_NORMAL);

}
#endif

/*
** The following global variable is incremented whenever the library
** attempts to open a temporary file.  This information is used for
** testing and analysis only.  
................................................................................
** conditions above is not true, the pager was in error state when this
** function was called, or because the memory allocation attempt failed, 
** then *pPageSize is set to the old, retained page size before returning.
*/
int sqlite3PagerSetPagesize(Pager *pPager, u16 *pPageSize, int nReserve){
  int rc = pPager->errCode;

  /* It is not possible to do a full assert_pager_state() here, as this
  ** function may be called from within PagerOpen(), before the state
  ** of the Pager object is internally consistent.
  */
  assert( rc==SQLITE_OK || pPager->eState==PAGER_ERROR );

  if( rc==SQLITE_OK ){
    u16 pageSize = *pPageSize;
    assert( pageSize==0 || (pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE) );
    if( (pPager->memDb==0 || pPager->dbSize==0)
     && sqlite3PcacheRefCount(pPager->pPCache)==0 
     && pageSize && pageSize!=pPager->pageSize 
    ){
      char *pNew;                 /* New temp space */
      i64 nByte = 0;
      if( pPager->eState>PAGER_OPEN && isOpen(pPager->fd) ){
        rc = sqlite3OsFileSize(pPager->fd, &nByte);
        if( rc!=SQLITE_OK ) return rc;
      }
      pNew = (char *)sqlite3PageMalloc(pageSize);
      if( !pNew ){
        rc = SQLITE_NOMEM;
      }else{
        pager_reset(pPager);
        pPager->dbSize = nByte/pageSize;
        pPager->pageSize = pageSize;
        sqlite3PageFree(pPager->pTmpSpace);
        pPager->pTmpSpace = pNew;
        sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
      }
    }
    *pPageSize = (u16)pPager->pageSize;
................................................................................
** Attempt to set the maximum database page count if mxPage is positive. 
** Make no changes if mxPage is zero or negative.  And never reduce the
** maximum page count below the current size of the database.
**
** Regardless of mxPage, return the current maximum page count.
*/
int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){

  if( mxPage>0 ){
    pPager->mxPgno = mxPage;
  }
  if( pPager->eState!=PAGER_OPEN && pPager->mxPgno<pPager->dbSize ){

    pPager->mxPgno = pPager->dbSize;
  }
  return pPager->mxPgno;
}

/*
** The following set of routines are used to disable the simulated
** I/O error mechanism.  These routines are used to avoid simulated
................................................................................
      rc = SQLITE_OK;
    }
  }
  return rc;
}

/*
** This function may only be called when a read-transaction is open on
** the pager. It returns the total number of pages in the database.

**
** However, if the file is between 1 and <page-size> bytes in size, then 
** this is considered a 1 page file.









*/
int sqlite3PagerPagecount(Pager *pPager, int *pnPage){




























  assert( pPager->eState>=PAGER_READER );
  assert( pPager->eState!=PAGER_WRITER_FINISHED );
  *pnPage = (int)pPager->dbSize;















  return SQLITE_OK;
}


/*
** Try to obtain a lock of type locktype on the database file. If
** a similar or greater lock is already held, this function is a no-op
................................................................................
** Return SQLITE_OK on success and an error code if we cannot obtain
** the lock. If the lock is obtained successfully, set the Pager.state 
** variable to locktype before returning.
*/
static int pager_wait_on_lock(Pager *pPager, int locktype){
  int rc;                              /* Return code */












  /* Check that this is either a no-op (because the requested lock is 
  ** already held, or one of the transistions that the busy-handler
  ** may be invoked during, according to the comment above
  ** sqlite3PagerSetBusyhandler().
  */
  assert( (pPager->eLock>=locktype)
       || (pPager->eLock==NO_LOCK && locktype==SHARED_LOCK)
       || (pPager->eLock==RESERVED_LOCK && locktype==EXCLUSIVE_LOCK)
  );




  do {

    rc = pagerLockDb(pPager, locktype);
  }while( rc==SQLITE_BUSY && pPager->xBusyHandler(pPager->pBusyHandlerArg) );





  return rc;
}

/*
** Function assertTruncateConstraint(pPager) checks that one of the 
** following is true for all dirty pages currently in the page-cache:
**
................................................................................
/*
** Truncate the in-memory database file image to nPage pages. This 
** function does not actually modify the database file on disk. It 
** just sets the internal state of the pager object so that the 
** truncation will be done when the current transaction is committed.
*/
void sqlite3PagerTruncateImage(Pager *pPager, Pgno nPage){

  assert( pPager->dbSize>=nPage );
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
  pPager->dbSize = nPage;
  assertTruncateConstraint(pPager);
}


/*
** This function is called before attempting a hot-journal rollback. It
................................................................................
** to the caller.
*/
int sqlite3PagerClose(Pager *pPager){
  u8 *pTmp = (u8 *)pPager->pTmpSpace;

  disable_simulated_io_errors();
  sqlite3BeginBenignMalloc();
  /* pPager->errCode = 0; */
  pPager->exclusiveMode = 0;
#ifndef SQLITE_OMIT_WAL
  sqlite3WalClose(pPager->pWal,
    (pPager->noSync ? 0 : pPager->sync_flags), 
    pPager->pageSize, pTmp
  );
  pPager->pWal = 0;
#endif
  pager_reset(pPager);
  if( MEMDB ){
    pager_unlock(pPager);
  }else{
    /* If it is open, sync the journal file before calling UnlockAndRollback.
    ** If this is not done, then an unsynced portion of the open journal 

    ** file may be played back into the database. If a power failure occurs 
    ** while this is happening, the database could become corrupt.
    **
    ** If an error occurs while trying to sync the journal, shift the pager
    ** into the ERROR state. This causes UnlockAndRollback to unlock the
    ** database and close the journal file without attempting to roll it
    ** back or finalize it. The next database user will have to do hot-journal
    ** rollback before accessing the database file.
    */
    if( isOpen(pPager->jfd) ){
      pager_error(pPager, pagerSyncHotJournal(pPager));
    }
    pagerUnlockAndRollback(pPager);
  }
  sqlite3EndBenignMalloc();
  enable_simulated_io_errors();
  PAGERTRACE(("CLOSE %d\n", PAGERID(pPager)));
  IOTRACE(("CLOSE %p\n", pPager))
................................................................................
}

/*
** Sync the journal. In other words, make sure all the pages that have
** been written to the journal have actually reached the surface of the
** disk and can be restored in the event of a hot-journal rollback.
**
** If the Pager.noSync flag is set, then this function is a no-op.
** Otherwise, the actions required depend on the journal-mode and the 
** device characteristics of the the file-system, as follows:
**
**   * If the journal file is an in-memory journal file, no action need
**     be taken.
**
**   * Otherwise, if the device does not support the SAFE_APPEND property,
**     then the nRec field of the most recently written journal header
**     is updated to contain the number of journal records that have
................................................................................
**     if( NOT SAFE_APPEND ){
**       if( <full-sync mode> ) xSync(<journal file>);
**       <update nRec field>
**     } 
**     if( NOT SEQUENTIAL ) xSync(<journal file>);
**   }
**



** If successful, this routine clears the PGHDR_NEED_SYNC flag of every 
** page currently held in memory before returning SQLITE_OK. If an IO
** error is encountered, then the IO error code is returned to the caller.
*/
static int syncJournal(Pager *pPager, int newHdr){
  int rc;                         /* Return code */

  assert( pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );
  assert( !pagerUseWal(pPager) );

  rc = sqlite3PagerExclusiveLock(pPager);
  if( rc!=SQLITE_OK ) return rc;

  if( !pPager->noSync ){
    assert( !pPager->tempFile );
    if( isOpen(pPager->jfd) && pPager->journalMode!=PAGER_JOURNALMODE_MEMORY ){

      const int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
      assert( isOpen(pPager->jfd) );

      if( 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
        /* This block deals with an obscure problem. If the last connection
        ** that wrote to this database was operating in persistent-journal
        ** mode, then the journal file may at this point actually be larger
................................................................................
        PAGERTRACE(("SYNC journal of %d\n", PAGERID(pPager)));
        IOTRACE(("JSYNC %p\n", pPager))
        rc = sqlite3OsSync(pPager->jfd, pPager->sync_flags| 
          (pPager->sync_flags==SQLITE_SYNC_FULL?SQLITE_SYNC_DATAONLY:0)
        );
        if( rc!=SQLITE_OK ) return rc;
      }

      pPager->journalHdr = pPager->journalOff;
      if( newHdr && 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
        pPager->nRec = 0;
        rc = writeJournalHdr(pPager);
        if( rc!=SQLITE_OK ) return rc;
      }





    }else{
      pPager->journalHdr = pPager->journalOff;

    }
  }

  /* Unless the pager is in noSync mode, the journal file was just 
  ** successfully synced. Either way, clear the PGHDR_NEED_SYNC flag on 
  ** all pages.
  */
  sqlite3PcacheClearSyncFlags(pPager->pPCache);
  pPager->eState = PAGER_WRITER_DBMOD;
  assert( assert_pager_state(pPager) );
  return SQLITE_OK;
}

/*
** The argument is the first in a linked list of dirty pages connected
** by the PgHdr.pDirty pointer. This function writes each one of the
** in-memory pages in the list to the database file. The argument may
................................................................................
** the database file.
**
** If everything is successful, SQLITE_OK is returned. If an IO error 
** occurs, an IO error code is returned. Or, if the EXCLUSIVE lock cannot
** be obtained, SQLITE_BUSY is returned.
*/
static int pager_write_pagelist(Pager *pPager, PgHdr *pList){
  int rc = SQLITE_OK;                  /* Return code */

  /* This function is only called for rollback pagers in WRITER_DBMOD state. */















  assert( !pagerUseWal(pPager) );
  assert( pPager->eState==PAGER_WRITER_DBMOD );
  assert( pPager->eLock==EXCLUSIVE_LOCK );


  /* If the file is a temp-file has not yet been opened, open it now. It
  ** is not possible for rc to be other than SQLITE_OK if this branch
  ** is taken, as pager_wait_on_lock() is a no-op for temp-files.
  */
  if( !isOpen(pPager->fd) ){
    assert( pPager->tempFile && rc==SQLITE_OK );
................................................................................
    rc = pagerOpentemp(pPager, pPager->fd, pPager->vfsFlags);
  }

  /* Before the first write, give the VFS a hint of what the final
  ** file size will be.
  */
  assert( rc!=SQLITE_OK || isOpen(pPager->fd) );
  if( rc==SQLITE_OK && pPager->dbSize>pPager->dbHintSize ){
    sqlite3_int64 szFile = pPager->pageSize * (sqlite3_int64)pPager->dbSize;
    sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_SIZE_HINT, &szFile);
    pPager->dbHintSize = pPager->dbSize;
  }

  while( rc==SQLITE_OK && pList ){
    Pgno pgno = pList->pgno;

    /* If there are dirty pages in the page cache with page numbers greater
    ** than Pager.dbSize, this means sqlite3PagerTruncateImage() was called to
................................................................................
    **
    ** Also, do not write out any page that has the PGHDR_DONT_WRITE flag
    ** set (set by sqlite3PagerDontWrite()).
    */
    if( pgno<=pPager->dbSize && 0==(pList->flags&PGHDR_DONT_WRITE) ){
      i64 offset = (pgno-1)*(i64)pPager->pageSize;   /* Offset to write */
      char *pData;                                   /* Data to write */    

      assert( (pList->flags&PGHDR_NEED_SYNC)==0 );

      /* Encode the database */
      CODEC2(pPager, pList->pData, pgno, 6, return SQLITE_NOMEM, pData);

      /* Write out the page data. */
      rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize, offset);

................................................................................
    }
    if( rc==SQLITE_OK ){
      rc = pagerWalFrames(pPager, pPg, 0, 0, 0);
    }
  }else{
  
    /* Sync the journal file if required. */
    if( pPg->flags&PGHDR_NEED_SYNC 
     || pPager->eState==PAGER_WRITER_CACHEMOD




    ){



      rc = syncJournal(pPager, 1);
    }
  
    /* If the page number of this page is larger than the current size of
    ** the database image, it may need to be written to the sub-journal.
    ** This is because the call to pager_write_pagelist() below will not
    ** actually write data to the file in this case.
    **
................................................................................
        rc==SQLITE_OK && pPg->pgno>pPager->dbSize && subjRequiresPage(pPg)
    ) ){
      rc = subjournalPage(pPg);
    }
  
    /* Write the contents of the page out to the database file. */
    if( rc==SQLITE_OK ){
      assert( (pPg->flags&PGHDR_NEED_SYNC)==0 );
      rc = pager_write_pagelist(pPager, pPg);
    }
  }

  /* Mark the page as clean. */
  if( rc==SQLITE_OK ){
    PAGERTRACE(("STRESS %d page %d\n", PAGERID(pPager), pPg->pgno));
................................................................................
    ** opening the file until the first call to OsWrite().
    **
    ** This branch is also run for an in-memory database. An in-memory
    ** database is the same as a temp-file that is never written out to
    ** disk and uses an in-memory rollback journal.
    */ 
    tempFile = 1;
    pPager->eState = PAGER_READER;
    pPager->eLock = EXCLUSIVE_LOCK;
    readOnly = (vfsFlags&SQLITE_OPEN_READONLY);
  }

  /* The following call to PagerSetPagesize() serves to set the value of 
  ** Pager.pageSize and to allocate the Pager.pTmpSpace buffer.
  */
  if( rc==SQLITE_OK ){
................................................................................
  IOTRACE(("OPEN %p %s\n", pPager, pPager->zFilename))

  pPager->useJournal = (u8)useJournal;
  pPager->noReadlock = (noReadlock && readOnly) ?1:0;
  /* pPager->stmtOpen = 0; */
  /* pPager->stmtInUse = 0; */
  /* pPager->nRef = 0; */

  /* pPager->stmtSize = 0; */
  /* pPager->stmtJSize = 0; */
  /* pPager->nPage = 0; */
  pPager->mxPgno = SQLITE_MAX_PAGE_COUNT;
  /* pPager->state = PAGER_UNLOCK; */
#if 0
  assert( pPager->state == (tempFile ? PAGER_EXCLUSIVE : PAGER_UNLOCK) );
#endif
  /* pPager->errMask = 0; */
  pPager->tempFile = (u8)tempFile;
  assert( tempFile==PAGER_LOCKINGMODE_NORMAL 
          || tempFile==PAGER_LOCKINGMODE_EXCLUSIVE );
  assert( PAGER_LOCKINGMODE_EXCLUSIVE==1 );
  pPager->exclusiveMode = (u8)tempFile; 
  pPager->changeCountDone = pPager->tempFile;
  pPager->memDb = (u8)memDb;
  pPager->readOnly = (u8)readOnly;

  assert( useJournal || pPager->tempFile );
  pPager->noSync = pPager->tempFile;
  pPager->fullSync = pPager->noSync ?0:1;
  pPager->sync_flags = SQLITE_SYNC_NORMAL;
  /* pPager->pFirst = 0; */
  /* pPager->pFirstSynced = 0; */
  /* pPager->pLast = 0; */
................................................................................
*/
static int hasHotJournal(Pager *pPager, int *pExists){
  sqlite3_vfs * const pVfs = pPager->pVfs;
  int rc = SQLITE_OK;           /* Return code */
  int exists = 1;               /* True if a journal file is present */
  int jrnlOpen = !!isOpen(pPager->jfd);


  assert( pPager->useJournal );
  assert( isOpen(pPager->fd) );
  assert( pPager->eState==PAGER_OPEN );

  assert( jrnlOpen==0 || ( sqlite3OsDeviceCharacteristics(pPager->jfd) &
    SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN
  ));

  *pExists = 0;
  if( !jrnlOpen ){
    rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
  }
  if( rc==SQLITE_OK && exists ){
    int locked = 0;             /* True if some process holds a RESERVED lock */

    /* Race condition here:  Another process might have been holding the
    ** the RESERVED lock and have a journal open at the sqlite3OsAccess() 
    ** call above, but then delete the journal and drop the lock before
    ** we get to the following sqlite3OsCheckReservedLock() call.  If that
    ** is the case, this routine might think there is a hot journal when
    ** in fact there is none.  This results in a false-positive which will
    ** be dealt with by the playback routine.  Ticket #3883.
    */
    rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
    if( rc==SQLITE_OK && !locked ){
      Pgno nPage;                 /* Number of pages in database file */

      /* Check the size of the database file. If it consists of 0 pages,
      ** then delete the journal file. See the header comment above for 
      ** the reasoning here.  Delete the obsolete journal file under
      ** a RESERVED lock to avoid race conditions and to avoid violating
      ** [H33020].
      */
      rc = pagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK ){
        if( nPage==0 ){
          sqlite3BeginBenignMalloc();
          if( pagerLockDb(pPager, RESERVED_LOCK)==SQLITE_OK ){
            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
            pagerUnlockDb(pPager, SHARED_LOCK);
          }
          sqlite3EndBenignMalloc();
        }else{
          /* The journal file exists and no other connection has a reserved
          ** or greater lock on the database file. Now check that there is
          ** at least one non-zero bytes at the start of the journal file.
          ** If there is, then we consider this journal to be hot. If not, 
................................................................................
**
** Otherwise, if everything is successful, SQLITE_OK is returned. If an
** IO error occurs while locking the database, checking for a hot-journal
** file or rolling back a journal file, the IO error code is returned.
*/
int sqlite3PagerSharedLock(Pager *pPager){
  int rc = SQLITE_OK;                /* Return code */


  /* This routine is only called from b-tree and only when there are no
  ** outstanding pages. This implies that the pager state should either
  ** be OPEN or READER. READER is only possible if the pager is or was in 
  ** exclusive access mode.
  */
  assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
  assert( assert_pager_state(pPager) );
  assert( pPager->eState==PAGER_OPEN || pPager->eState==PAGER_READER );
  if( NEVER(MEMDB && pPager->errCode) ){ return pPager->errCode; }





  if( !pagerUseWal(pPager) && pPager->eState==PAGER_OPEN ){
    int bHotJournal = 1;          /* True if there exists a hot journal-file */


    assert( !MEMDB );
    assert( pPager->noReadlock==0 || pPager->readOnly );










    if( pPager->noReadlock==0 ){



      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
      if( rc!=SQLITE_OK ){


        assert( pPager->eLock==NO_LOCK || pPager->eLock==UNKNOWN_LOCK );
        goto failed;
      }
    }


    /* If a journal file exists, and there is no RESERVED lock on the
    ** database file, then it either needs to be played back or deleted.
    */
    if( pPager->eLock<=SHARED_LOCK ){

      rc = hasHotJournal(pPager, &bHotJournal);
    }
    if( rc!=SQLITE_OK ){
      goto failed;
    }

    if( bHotJournal ){
      /* Get an EXCLUSIVE lock on the database file. At this point it is
      ** important that a RESERVED lock is not obtained on the way to the
      ** EXCLUSIVE lock. If it were, another process might open the
      ** database file, detect the RESERVED lock, and conclude that the
      ** database is safe to read while this process is still rolling the 
      ** hot-journal back.
      ** 
      ** Because the intermediate RESERVED lock is not requested, any
      ** other process attempting to access the database file will get to 
      ** this point in the code and fail to obtain its own EXCLUSIVE lock 
      ** on the database file.
      **
      ** Unless the pager is in locking_mode=exclusive mode, the lock is
      ** downgraded to SHARED_LOCK before this function returns.
      */

      rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
      if( rc!=SQLITE_OK ){

        goto failed;
      }

 

      /* If it is not already open and the file exists on disk, open the 
      ** journal for read/write access. Write access is required because 
      ** in exclusive-access mode the file descriptor will be kept open 
      ** and possibly used for a transaction later on. Also, write-access 
      ** is usually required to finalize the journal in journal_mode=persist 
      ** mode (and also for journal_mode=truncate on some systems).
      **
      ** If the journal does not exist, it usually means that some 
      ** other connection managed to get in and roll it back before 
      ** this connection obtained the exclusive lock above. Or, it 
      ** may mean that the pager was in the error-state when this
      ** function was called and the journal file does not exist.
      */
      if( !isOpen(pPager->jfd) ){

        sqlite3_vfs * const pVfs = pPager->pVfs;
        int bExists;              /* True if journal file exists */
        rc = sqlite3OsAccess(
            pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &bExists);
        if( rc==SQLITE_OK && bExists ){

          int fout = 0;
          int f = SQLITE_OPEN_READWRITE|SQLITE_OPEN_MAIN_JOURNAL;
          assert( !pPager->tempFile );
          rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &fout);
          assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
          if( rc==SQLITE_OK && fout&SQLITE_OPEN_READONLY ){
            rc = SQLITE_CANTOPEN_BKPT;
            sqlite3OsClose(pPager->jfd);
          }







        }
      }













 
      /* Playback and delete the journal.  Drop the database write
      ** lock and reacquire the read lock. Purge the cache before
      ** playing back the hot-journal so that we don't end up with
      ** an inconsistent cache.  Sync the hot journal before playing
      ** it back since the process that crashed and left the hot journal
      ** probably did not sync it and we are required to always sync
      ** the journal before playing it back.
      */
      if( isOpen(pPager->jfd) ){
        assert( rc==SQLITE_OK );
        rc = pagerSyncHotJournal(pPager);
        if( rc==SQLITE_OK ){
          rc = pager_playback(pPager, 1);
          pPager->eState = PAGER_OPEN;
        }
      }else if( !pPager->exclusiveMode ){
        pagerUnlockDb(pPager, SHARED_LOCK);
      }

      if( rc!=SQLITE_OK ){
        /* This branch is taken if an error occurs while trying to open
        ** or roll back a hot-journal while holding an EXCLUSIVE lock. The
        ** pager_unlock() routine will be called before returning to unlock
        ** the file. If the unlock attempt fails, then Pager.eLock must be
        ** set to UNKNOWN_LOCK (see the comment above the #define for 
        ** UNKNOWN_LOCK above for an explanation). 
        **
        ** In order to get pager_unlock() to do this, set Pager.eState to
        ** PAGER_ERROR now. This is not actually counted as a transition
        ** to ERROR state in the state diagram at the top of this file,
        ** since we know that the same call to pager_unlock() will very
        ** shortly transition the pager object to the OPEN state. Calling
        ** assert_pager_state() would fail now, as it should not be possible
        ** to be in ERROR state when there are zero outstanding page 
        ** references.
        */
        pager_error(pPager, rc);
        goto failed;
      }

      assert( pPager->eState==PAGER_OPEN );
      assert( (pPager->eLock==SHARED_LOCK)
           || (pPager->exclusiveMode && pPager->eLock>SHARED_LOCK)
      );
    }

    if( !pPager->tempFile 
     && (pPager->pBackup || sqlite3PcachePagecount(pPager->pPCache)>0) 
    ){
      /* The shared-lock has just been acquired on the database file
      ** and there are already pages in the cache (from a previous
      ** read or write transaction).  Check to see if the database
      ** has been modified.  If the database has changed, flush the
      ** cache.
      **
      ** Database changes is detected by looking at 15 bytes beginning
................................................................................
      ** other bytes change randomly with each file change when
      ** a codec is in use.
      ** 
      ** There is a vanishingly small chance that a change will not be 
      ** detected.  The chance of an undetected change is so small that
      ** it can be neglected.
      */
      Pgno nPage = 0;
      char dbFileVers[sizeof(pPager->dbFileVers)];




      rc = pagerPagecount(pPager, &nPage);
      if( rc ) goto failed;


      if( nPage>0 ){
        IOTRACE(("CKVERS %p %d\n", pPager, sizeof(dbFileVers)));
        rc = sqlite3OsRead(pPager->fd, &dbFileVers, sizeof(dbFileVers), 24);
        if( rc!=SQLITE_OK ){
          goto failed;
        }
................................................................................
        memset(dbFileVers, 0, sizeof(dbFileVers));
      }

      if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
        pager_reset(pPager);
      }
    }


    /* If there is a WAL file in the file-system, open this database in WAL
    ** mode. Otherwise, the following function call is a no-op.
    */
    rc = pagerOpenWalIfPresent(pPager);
  }

  if( pagerUseWal(pPager) && rc==SQLITE_OK ){
    rc = pagerBeginReadTransaction(pPager);
  }

  if( pPager->eState==PAGER_OPEN && rc==SQLITE_OK ){
    rc = pagerPagecount(pPager, &pPager->dbSize);
  }

 failed:
  if( rc!=SQLITE_OK ){

    pager_unlock(pPager);
    assert( pPager->eState==PAGER_OPEN );
  }else{
    pPager->eState = PAGER_READER;
  }
  return rc;
}

/*
** If the reference count has reached zero, rollback any active
** transaction and unlock the pager.
**
** Except, in locking_mode=EXCLUSIVE when there is nothing to in
** the rollback journal, the unlock is not performed and there is
** nothing to rollback, so this routine is a no-op.
*/ 
static void pagerUnlockIfUnused(Pager *pPager){
  if( (sqlite3PcacheRefCount(pPager->pPCache)==0) ){


    pagerUnlockAndRollback(pPager);
  }
}

/*
** Acquire a reference to page number pgno in pager pPager (a page
** reference has type DbPage*). If the requested reference is 
................................................................................
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int noContent       /* Do not bother reading content from disk if true */
){
  int rc;
  PgHdr *pPg;

  assert( pPager->eState>=PAGER_READER );
  assert( assert_pager_state(pPager) );


  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }

  /* If the pager is in the error state, return an error immediately. 
  ** Otherwise, request the page from the PCache layer. */
................................................................................
    assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) );
    PAGER_INCR(pPager->nHit);
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.  */


    PAGER_INCR(pPager->nMiss);
    pPg = *ppPage;
    pPg->pPager = pPager;

    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
    ** number greater than this, or the unused locking-page, is requested. */
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto pager_acquire_err;
    }






    if( MEMDB || pPager->dbSize<(int)pgno || noContent || !isOpen(pPager->fd) ){
      if( pgno>pPager->mxPgno ){
        rc = SQLITE_FULL;
        goto pager_acquire_err;
      }
      if( noContent ){
        /* Failure to set the bits in the InJournal bit-vectors is benign.
        ** It merely means that we might do some extra work to journal a 
................................................................................
** has ever happened.
*/
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
  PgHdr *pPg = 0;
  assert( pPager!=0 );
  assert( pgno!=0 );
  assert( pPager->pPCache!=0 );
  assert( pPager->eState>=PAGER_READER );
  sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &pPg);
  return pPg;
}

/*
** Release a page reference.
**
................................................................................
**
** Return SQLITE_OK if everything is successful. Otherwise, return 
** SQLITE_NOMEM if the attempt to allocate Pager.pInJournal fails, or 
** an IO error code if opening or writing the journal file fails.
*/
static int pager_open_journal(Pager *pPager){
  int rc = SQLITE_OK;                        /* Return code */

  sqlite3_vfs * const pVfs = pPager->pVfs;   /* Local cache of vfs pointer */


  assert( pPager->eState==PAGER_WRITER_LOCKED );

  assert( assert_pager_state(pPager) );
  assert( pPager->pInJournal==0 );
  
  /* If already in the error state, this function is a no-op.  But on
  ** the other hand, this routine is never called if we are already in
  ** an error state. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  if( !pagerUseWal(pPager) && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){


    pPager->pInJournal = sqlite3BitvecCreate(pPager->dbSize);
    if( pPager->pInJournal==0 ){
      return SQLITE_NOMEM;
    }
  
    /* Open the journal file if it is not already open. */
    if( !isOpen(pPager->jfd) ){
      if( pPager->journalMode==PAGER_JOURNALMODE_MEMORY ){
        sqlite3MemJournalOpen(pPager->jfd);
      }else{
        const int flags =                   /* VFS flags to open journal file */
          SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|
          (pPager->tempFile ? 
            (SQLITE_OPEN_DELETEONCLOSE|SQLITE_OPEN_TEMP_JOURNAL):
            (SQLITE_OPEN_MAIN_JOURNAL)
          );
  #ifdef SQLITE_ENABLE_ATOMIC_WRITE
        rc = sqlite3JournalOpen(
            pVfs, pPager->zJournal, pPager->jfd, flags, jrnlBufferSize(pPager)
        );
  #else
        rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, flags, 0);
  #endif
      }
      assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
    }
  
  
    /* Write the first journal header to the journal file and open 
    ** the sub-journal if necessary.
    */
    if( rc==SQLITE_OK ){
      /* TODO: Check if all of these are really required. */



      pPager->nRec = 0;
      pPager->journalOff = 0;
      pPager->setMaster = 0;
      pPager->journalHdr = 0;
      rc = writeJournalHdr(pPager);
    }
  }

  if( rc!=SQLITE_OK ){
    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
  }else{
    assert( pPager->eState==PAGER_WRITER_LOCKED );
    pPager->eState = PAGER_WRITER_CACHEMOD;
  }

  return rc;
}

/*
** Begin a write-transaction on the specified pager object. If a 
** write-transaction has already been opened, this function is a no-op.
**
** If the exFlag argument is false, then acquire at least a RESERVED
** lock on the database file. If exFlag is true, then acquire at least
** an EXCLUSIVE lock. If such a lock is already held, no locking 
** functions need be called.
**








** If the subjInMemory argument is non-zero, then any sub-journal opened
** within this transaction will be opened as an in-memory file. This
** has no effect if the sub-journal is already opened (as it may be when
** running in exclusive mode) or if the transaction does not require a
** sub-journal. If the subjInMemory argument is zero, then any required
** sub-journal is implemented in-memory if pPager is an in-memory database, 
** or using a temporary file otherwise.
*/
int sqlite3PagerBegin(Pager *pPager, int exFlag, int subjInMemory){
  int rc = SQLITE_OK;
  assert( pPager->eState>=PAGER_READER );
  pPager->subjInMemory = (u8)subjInMemory;

  if( pPager->eState==PAGER_READER ){
    assert( pPager->pInJournal==0 );


    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);

        if( rc!=SQLITE_OK ){
          return rc;
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
      ** PAGER_RESERVED state. Otherwise, return an error code to the caller.
      ** The busy-handler is not invoked if another connection already
      ** holds the write-lock. If possible, the upper layer will call it.






      */
      rc = sqlite3WalBeginWriteTransaction(pPager->pWal);








    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
      */
      rc = pagerLockDb(pPager, RESERVED_LOCK);
      if( rc==SQLITE_OK && exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }

    if( rc==SQLITE_OK ){
      /* Change to WRITER_LOCKED state.
      **
      ** WAL mode sets Pager.eState to PAGER_WRITER_LOCKED or CACHEMOD
      ** when it has an open transaction, but never to DBMOD or FINISHED.
      ** This is because in those states the code to roll back savepoint 
      ** transactions may copy data from the sub-journal into the database 
      ** file as well as into the page cache. Which would be incorrect in 
      ** WAL mode.
      */
      pPager->eState = PAGER_WRITER_LOCKED;
      pPager->dbHintSize = pPager->dbSize;
      pPager->dbFileSize = pPager->dbSize;
      pPager->dbOrigSize = pPager->dbSize;
      pPager->journalOff = 0;
    }

    assert( rc==SQLITE_OK || pPager->eState==PAGER_READER );
    assert( rc!=SQLITE_OK || pPager->eState==PAGER_WRITER_LOCKED );
    assert( assert_pager_state(pPager) );
  }

  PAGERTRACE(("TRANSACTION %d\n", PAGERID(pPager)));
  return rc;
}

/*
................................................................................
** of any open savepoints as appropriate.
*/
static int pager_write(PgHdr *pPg){
  void *pData = pPg->pData;
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;

  /* This routine is not called unless a write-transaction has already 
  ** been started. The journal file may or may not be open at this point.
  ** It is never called in the ERROR state.
  */
  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );

  /* If an error has been previously detected, report the same error


  ** again. This should not happen, but the check provides robustness. */
  if( NEVER(pPager->errCode) )  return pPager->errCode;

  /* Higher-level routines never call this function if database is not
  ** writable.  But check anyway, just for robustness. */
  if( NEVER(pPager->readOnly) ) return SQLITE_PERM;



  CHECK_PAGE(pPg);

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  sqlite3PcacheMakeDirty(pPg);
  if( pageInJournal(pPg) && !subjRequiresPage(pPg) ){
    assert( !pagerUseWal(pPager) );
    assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
  }else{

    /* If we get this far, it means that the page needs to be
    ** written to the transaction journal or the checkpoint journal
    ** or both.
    **
    ** Higher level routines have already obtained the necessary locks
    ** to begin the write-transaction, but the rollback journal might not 
    ** yet be open. Open it now if this is the case.
    */

    if( pPager->eState==PAGER_WRITER_LOCKED ){




      rc = pager_open_journal(pPager);
      if( rc!=SQLITE_OK ) return rc;
    }
    assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
    assert( assert_pager_state(pPager) );
  
    /* The transaction journal now exists and we have a RESERVED or an
    ** EXCLUSIVE lock on the main database file.  Write the current page to
    ** the transaction journal if it is not there already.
    */
    if( !pageInJournal(pPg) && !pagerUseWal(pPager) ){
      assert( pagerUseWal(pPager)==0 );
      if( pPg->pgno<=pPager->dbOrigSize && isOpen(pPager->jfd) ){
        u32 cksum;
        char *pData2;
        i64 iOff = pPager->journalOff;

        /* We should never write to the journal file the page that
        ** contains the database locks.  The following assert verifies
        ** that we do not. */
        assert( pPg->pgno!=PAGER_MJ_PGNO(pPager) );

        assert( pPager->journalHdr<=pPager->journalOff );
        CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
        cksum = pager_cksum(pPager, (u8*)pData2);

        /* Even if an IO or diskfull error occurs while journalling the
        ** page in the block above, set the need-sync flag for the page.
        ** Otherwise, when the transaction is rolled back, the logic in
        ** playback_one_page() will think that the page needs to be restored
        ** in the database file. And if an IO error occurs while doing so,
        ** then corruption may follow.
        */
        pPg->flags |= PGHDR_NEED_SYNC;

        rc = write32bits(pPager->jfd, iOff, pPg->pgno);
        if( rc!=SQLITE_OK ) return rc;
        rc = sqlite3OsWrite(pPager->jfd, pData2, pPager->pageSize, iOff+4);



        if( rc!=SQLITE_OK ) return rc;
        rc = write32bits(pPager->jfd, iOff+pPager->pageSize+4, cksum);

        if( rc!=SQLITE_OK ) return rc;

        IOTRACE(("JOUT %p %d %lld %d\n", pPager, pPg->pgno, 
                 pPager->journalOff, pPager->pageSize));
        PAGER_INCR(sqlite3_pager_writej_count);
        PAGERTRACE(("JOURNAL %d page %d needSync=%d hash(%08x)\n",
             PAGERID(pPager), pPg->pgno, 
             ((pPg->flags&PGHDR_NEED_SYNC)?1:0), pager_pagehash(pPg)));

        pPager->journalOff += 8 + pPager->pageSize;


















        pPager->nRec++;
        assert( pPager->pInJournal!=0 );
        rc = sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
        testcase( rc==SQLITE_NOMEM );
        assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
        rc |= addToSavepointBitvecs(pPager, pPg->pgno);
        if( rc!=SQLITE_OK ){
          assert( rc==SQLITE_NOMEM );
          return rc;
        }
      }else{
        if( pPager->eState!=PAGER_WRITER_DBMOD ){
          pPg->flags |= PGHDR_NEED_SYNC;

        }
        PAGERTRACE(("APPEND %d page %d needSync=%d\n",
                PAGERID(pPager), pPg->pgno,
               ((pPg->flags&PGHDR_NEED_SYNC)?1:0)));
      }
    }
  
................................................................................
    if( subjRequiresPage(pPg) ){
      rc = subjournalPage(pPg);
    }
  }

  /* Update the database size and return.
  */

  if( pPager->dbSize<pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
................................................................................
int sqlite3PagerWrite(DbPage *pDbPage){
  int rc = SQLITE_OK;

  PgHdr *pPg = pDbPage;
  Pager *pPager = pPg->pPager;
  Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);

  assert( pPager->eState>=PAGER_WRITER_LOCKED );
  assert( pPager->eState!=PAGER_ERROR );
  assert( assert_pager_state(pPager) );

  if( nPagePerSector>1 ){
    Pgno nPageCount;          /* Total number of pages in database file */
    Pgno pg1;                 /* First page of the sector pPg is located on. */
    int nPage = 0;            /* Number of pages starting at pg1 to journal */
    int ii;                   /* Loop counter */
    int needSync = 0;         /* True if any page has PGHDR_NEED_SYNC */

................................................................................

    /* This trick assumes that both the page-size and sector-size are
    ** an integer power of 2. It sets variable pg1 to the identifier
    ** of the first page of the sector pPg is located on.
    */
    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

    nPageCount = pPager->dbSize;

    if( pPg->pgno>nPageCount ){
      nPage = (pPg->pgno - pg1)+1;
    }else if( (pg1+nPagePerSector-1)>nPageCount ){
      nPage = nPageCount+1-pg1;
    }else{
      nPage = nPagePerSector;
    }
    assert(nPage>0);
    assert(pg1<=pPg->pgno);
    assert((pg1+nPage)>pPg->pgno);


    for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
      Pgno pg = pg1+ii;
      PgHdr *pPage;
      if( pg==pPg->pgno || !sqlite3BitvecTest(pPager->pInJournal, pg) ){
        if( pg!=PAGER_MJ_PGNO(pPager) ){
          rc = sqlite3PagerGet(pPager, pg, &pPage);
          if( rc==SQLITE_OK ){
            rc = pager_write(pPage);
            if( pPage->flags&PGHDR_NEED_SYNC ){
              needSync = 1;

            }
            sqlite3PagerUnref(pPage);
          }
        }
      }else if( (pPage = pager_lookup(pPager, pg))!=0 ){
        if( pPage->flags&PGHDR_NEED_SYNC ){
          needSync = 1;
................................................................................
    /* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages 
    ** starting at pg1, then it needs to be set for all of them. Because
    ** writing to any of these nPage pages may damage the others, the
    ** journal file must contain sync()ed copies of all of them
    ** before any of them can be written out to the database file.
    */
    if( rc==SQLITE_OK && needSync ){
      assert( !MEMDB );
      for(ii=0; ii<nPage; ii++){
        PgHdr *pPage = pager_lookup(pPager, pg1+ii);
        if( pPage ){
          pPage->flags |= PGHDR_NEED_SYNC;
          sqlite3PagerUnref(pPage);
        }
      }

    }

    assert( pPager->doNotSyncSpill==1 );
    pPager->doNotSyncSpill--;
  }else{
    rc = pager_write(pDbPage);
  }
................................................................................
** with the SQLITE_ENABLE_ATOMIC_WRITE macro defined. In this case,
** if isDirect is non-zero, then the database file is updated directly
** by writing an updated version of page 1 using a call to the 
** sqlite3OsWrite() function.
*/
static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
  int rc = SQLITE_OK;

  assert( pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );

  /* Declare and initialize constant integer 'isDirect'. If the
  ** atomic-write optimization is enabled in this build, then isDirect
  ** is initialized to the value passed as the isDirectMode parameter
  ** to this function. Otherwise, it is always set to zero.
  **
  ** The idea is that if the atomic-write optimization is not
................................................................................
# define DIRECT_MODE 0
  assert( isDirectMode==0 );
  UNUSED_PARAMETER(isDirectMode);
#else
# define DIRECT_MODE isDirectMode
#endif


  if( !pPager->changeCountDone && pPager->dbSize>0 ){
    PgHdr *pPgHdr;                /* Reference to page 1 */
    u32 change_counter;           /* Initial value of change-counter field */

    assert( !pPager->tempFile && isOpen(pPager->fd) );

    /* Open page 1 of the file for writing. */
................................................................................
** If the EXCLUSIVE lock is already held or the attempt to obtain it is
** successful, or the connection is in WAL mode, SQLITE_OK is returned.
** Otherwise, either SQLITE_BUSY or an SQLITE_IOERR_XXX error code is 
** returned.
*/
int sqlite3PagerExclusiveLock(Pager *pPager){
  int rc = SQLITE_OK;
  assert( pPager->eState==PAGER_WRITER_CACHEMOD 
       || pPager->eState==PAGER_WRITER_DBMOD 
       || pPager->eState==PAGER_WRITER_LOCKED 
  );
  assert( assert_pager_state(pPager) );
  if( 0==pagerUseWal(pPager) ){
    rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
  }
  return rc;
}

/*
** Sync the database file for the pager pPager. zMaster points to the name
** of a master journal file that should be written into the individual
................................................................................
int sqlite3PagerCommitPhaseOne(
  Pager *pPager,                  /* Pager object */
  const char *zMaster,            /* If not NULL, the master journal name */
  int noSync                      /* True to omit the xSync on the db file */
){
  int rc = SQLITE_OK;             /* Return code */

  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
       || pPager->eState==PAGER_ERROR
  );
  assert( assert_pager_state(pPager) );

  /* If a prior error occurred, report that error again. */
  if( pPager->errCode ) return pPager->errCode;

  PAGERTRACE(("DATABASE SYNC: File=%s zMaster=%s nSize=%d\n", 
      pPager->zFilename, zMaster, pPager->dbSize));

  /* If no database changes have been made, return early. */
  if( pPager->eState<PAGER_WRITER_CACHEMOD ) return SQLITE_OK;

  if( MEMDB ){
    /* If this is an in-memory db, or no pages have been written to, or this
    ** function has already been called, it is mostly a no-op.  However, any
    ** backup in progress needs to be restarted.
    */
    sqlite3BackupRestart(pPager->pBackup);
  }else{
    if( pagerUseWal(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      if( pList ){
        rc = pagerWalFrames(pPager, pList, pPager->dbSize, 1, 
            (pPager->fullSync ? pPager->sync_flags : 0)
        );
      }
................................................................................
      PgHdr *pPg;
      assert( isOpen(pPager->jfd) 
           || pPager->journalMode==PAGER_JOURNALMODE_OFF 
           || pPager->journalMode==PAGER_JOURNALMODE_WAL 
      );
      if( !zMaster && isOpen(pPager->jfd) 
       && pPager->journalOff==jrnlBufferSize(pPager) 
       && pPager->dbSize>=pPager->dbOrigSize
       && (0==(pPg = sqlite3PcacheDirtyList(pPager->pPCache)) || 0==pPg->pDirty)
      ){
        /* Update the db file change counter via the direct-write method. The 
        ** following call will modify the in-memory representation of page 1 
        ** to include the updated change counter and then write page 1 
        ** directly to the database file. Because of the atomic-write 
        ** property of the host file-system, this is safe.
................................................................................
      ** reading data from the database file.
      **
      ** When journal_mode==OFF the dbOrigSize is always zero, so this
      ** block never runs if journal_mode=OFF.
      */
  #ifndef SQLITE_OMIT_AUTOVACUUM
      if( pPager->dbSize<pPager->dbOrigSize 
       && pPager->journalMode!=PAGER_JOURNALMODE_OFF
      ){
        Pgno i;                                   /* Iterator variable */
        const Pgno iSkip = PAGER_MJ_PGNO(pPager); /* Pending lock page */
        const Pgno dbSize = pPager->dbSize;       /* Database image size */ 
        pPager->dbSize = pPager->dbOrigSize;
        for( i=dbSize+1; i<=pPager->dbOrigSize; i++ ){
          if( !sqlite3BitvecTest(pPager->pInJournal, i) && i!=iSkip ){
................................................................................
      /* Write the master journal name into the journal file. If a master 
      ** journal file name has already been written to the journal file, 
      ** or if zMaster is NULL (no master journal), then this call is a no-op.
      */
      rc = writeMasterJournal(pPager, zMaster);
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  
      /* Sync the journal file and write all dirty pages to the database.
      ** If the atomic-update optimization is being used, this sync will not 
      ** create the journal file or perform any real IO.

      **
      ** Because the change-counter page was just modified, unless the
      ** atomic-update optimization is used it is almost certain that the
      ** journal requires a sync here. However, in locking_mode=exclusive
      ** on a system under memory pressure it is just possible that this is 
      ** not the case. In this case it is likely enough that the redundant
      ** xSync() call will be changed to a no-op by the OS anyhow. 
      */
      rc = syncJournal(pPager, 0);
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  

      rc = pager_write_pagelist(pPager,sqlite3PcacheDirtyList(pPager->pPCache));
      if( rc!=SQLITE_OK ){
        assert( rc!=SQLITE_IOERR_BLOCKED );
        goto commit_phase_one_exit;
      }
      sqlite3PcacheCleanAll(pPager->pPCache);
  
      /* If the file on disk is not the same size as the database image,
      ** then use pager_truncate to grow or shrink the file here.
      */
      if( pPager->dbSize!=pPager->dbFileSize ){
        Pgno nNew = pPager->dbSize - (pPager->dbSize==PAGER_MJ_PGNO(pPager));
        assert( pPager->eState==PAGER_WRITER_DBMOD );
        rc = pager_truncate(pPager, nNew);
        if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
      }
  
      /* Finally, sync the database file. */
      if( !pPager->noSync && !noSync ){
        rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
      }
      IOTRACE(("DBSYNC %p\n", pPager))
    }



  }

commit_phase_one_exit:
  if( rc==SQLITE_OK && !pagerUseWal(pPager) ){
    pPager->eState = PAGER_WRITER_FINISHED;
  }
  return rc;
}


/*
** When this function is called, the database file has been completely
** updated to reflect the changes made by the current transaction and
................................................................................
  int rc = SQLITE_OK;                  /* Return code */

  /* This routine should not be called if a prior error has occurred.
  ** But if (due to a coding error elsewhere in the system) it does get
  ** called, just return the same error code without doing anything. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_FINISHED
       || (pagerUseWal(pPager) && pPager->eState==PAGER_WRITER_CACHEMOD)
  );
  assert( assert_pager_state(pPager) );


  /* An optimization. If the database was not actually modified during
  ** this transaction, the pager is running in exclusive-mode and is
  ** using persistent journals, then this function is a no-op.
  **
  ** The start of the journal file currently contains a single journal 
  ** header with the nRec field set to 0. If such a journal is used as
  ** a hot-journal during hot-journal rollback, 0 changes will be made
  ** to the database file. So there is no need to zero the journal 
  ** header. Since the pager is in exclusive mode, there is no need
  ** to drop any locks either.
  */
  if( pPager->eState==PAGER_WRITER_LOCKED 
   && pPager->exclusiveMode 
   && pPager->journalMode==PAGER_JOURNALMODE_PERSIST
  ){
    assert( pPager->journalOff==JOURNAL_HDR_SZ(pPager) || !pPager->journalOff );
    pPager->eState = PAGER_READER;
    return SQLITE_OK;
  }

  PAGERTRACE(("COMMIT %d\n", PAGERID(pPager)));

  rc = pager_end_transaction(pPager, pPager->setMaster);
  return pager_error(pPager, rc);
}

/*
** If a write transaction is open, then all changes made within the 
** transaction are reverted and the current write-transaction is closed.
** The pager falls back to PAGER_READER state if successful, or PAGER_ERROR
** state if an error occurs.
**
** If the pager is already in PAGER_ERROR state when this function is called,
** it returns Pager.errCode immediately. No work is performed in this case.
**
** Otherwise, in rollback mode, this function performs two functions:
**
**   1) It rolls back the journal file, restoring all database file and 
**      in-memory cache pages to the state they were in when the transaction
**      was opened, and
**
**   2) It finalizes the journal file, so that it is not used for hot
**      rollback at any point in the future.
**
** Finalization of the journal file (task 2) is only performed if the 
** rollback is successful.
**

** In WAL mode, all cache-entries containing data modified within the
** current transaction are either expelled from the cache or reverted to
** their pre-transaction state by re-reading data from the database or
** WAL files. The WAL transaction is then closed.
























*/
int sqlite3PagerRollback(Pager *pPager){
  int rc = SQLITE_OK;                  /* Return code */
  PAGERTRACE(("ROLLBACK %d\n", PAGERID(pPager)));

  /* PagerRollback() is a no-op if called in READER or OPEN state. If
  ** the pager is already in the ERROR state, the rollback is not 
  ** attempted here. Instead, the error code is returned to the caller.
  */
  assert( assert_pager_state(pPager) );
  if( pPager->eState==PAGER_ERROR ) return pPager->errCode;
  if( pPager->eState<=PAGER_READER ) return SQLITE_OK;

  if( pagerUseWal(pPager) ){
    int rc2;

    rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
    rc2 = pager_end_transaction(pPager, pPager->setMaster);
    if( rc==SQLITE_OK ) rc = rc2;
  }else if( !isOpen(pPager->jfd) || pPager->eState==PAGER_WRITER_LOCKED ){

    rc = pager_end_transaction(pPager, 0);





  }else{


    rc = pager_playback(pPager, 0);



  }



  assert( pPager->eState==PAGER_READER || rc!=SQLITE_OK );
  assert( rc==SQLITE_OK || rc==SQLITE_FULL || (rc&0xFF)==SQLITE_IOERR );





  /* If an error occurs during a ROLLBACK, we can no longer trust the pager
  ** cache. So call pager_error() on the way out to make any error persistent.

  */
  return pager_error(pPager, rc);


}

/*
** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
u8 sqlite3PagerIsreadonly(Pager *pPager){
................................................................................
** This routine is used for testing and analysis only.
*/
int *sqlite3PagerStats(Pager *pPager){
  static int a[11];
  a[0] = sqlite3PcacheRefCount(pPager->pPCache);
  a[1] = sqlite3PcachePagecount(pPager->pPCache);
  a[2] = sqlite3PcacheGetCachesize(pPager->pPCache);
  a[3] = pPager->eState==PAGER_OPEN ? -1 : (int) pPager->dbSize;
  a[4] = pPager->eState;
  a[5] = pPager->errCode;
  a[6] = pPager->nHit;
  a[7] = pPager->nMiss;
  a[8] = 0;  /* Used to be pPager->nOvfl */
  a[9] = pPager->nRead;
  a[10] = pPager->nWrite;
  return a;
................................................................................
** If a memory allocation fails, SQLITE_NOMEM is returned. If an error 
** occurs while opening the sub-journal file, then an IO error code is
** returned. Otherwise, SQLITE_OK.
*/
int sqlite3PagerOpenSavepoint(Pager *pPager, int nSavepoint){
  int rc = SQLITE_OK;                       /* Return code */
  int nCurrent = pPager->nSavepoint;        /* Current number of savepoints */

  assert( pPager->eState>=PAGER_WRITER_LOCKED );
  assert( assert_pager_state(pPager) );

  if( nSavepoint>nCurrent && pPager->useJournal ){
    int ii;                                 /* Iterator variable */
    PagerSavepoint *aNew;                   /* New Pager.aSavepoint array */





    /* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
    ** if the allocation fails. Otherwise, zero the new portion in case a 
    ** malloc failure occurs while populating it in the for(...) loop below.
    */
    aNew = (PagerSavepoint *)sqlite3Realloc(
        pPager->aSavepoint, sizeof(PagerSavepoint)*nSavepoint
................................................................................
      return SQLITE_NOMEM;
    }
    memset(&aNew[nCurrent], 0, (nSavepoint-nCurrent) * sizeof(PagerSavepoint));
    pPager->aSavepoint = aNew;

    /* Populate the PagerSavepoint structures just allocated. */
    for(ii=nCurrent; ii<nSavepoint; ii++){
      aNew[ii].nOrig = pPager->dbSize;
      if( isOpen(pPager->jfd) && pPager->journalOff>0 ){
        aNew[ii].iOffset = pPager->journalOff;
      }else{
        aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
      }
      aNew[ii].iSubRec = pPager->nSubRec;
      aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager->dbSize);
      if( !aNew[ii].pInSavepoint ){
        return SQLITE_NOMEM;
      }
      if( pagerUseWal(pPager) ){
        sqlite3WalSavepoint(pPager->pWal, aNew[ii].aWalData);
      }
      pPager->nSavepoint = ii+1;
................................................................................
** then savepoint iSavepoint is also destroyed.
**
** This function may return SQLITE_NOMEM if a memory allocation fails,
** or an IO error code if an IO error occurs while rolling back a 
** savepoint. If no errors occur, SQLITE_OK is returned.
*/ 
int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint){
  int rc = pPager->errCode;       /* Return code */

  assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
  assert( iSavepoint>=0 || op==SAVEPOINT_ROLLBACK );

  if( rc==SQLITE_OK && iSavepoint<pPager->nSavepoint ){
    int ii;            /* Iterator variable */
    int nNew;          /* Number of remaining savepoints after this op. */

    /* Figure out how many savepoints will still be active after this
    ** operation. Store this value in nNew. Then free resources associated 
    ** with any savepoints that are destroyed by this operation.
    */
................................................................................
    ** the database file, so the playback operation can be skipped.
    */
    else if( pagerUseWal(pPager) || isOpen(pPager->jfd) ){
      PagerSavepoint *pSavepoint = (nNew==0)?0:&pPager->aSavepoint[nNew-1];
      rc = pagerPlaybackSavepoint(pPager, pSavepoint);
      assert(rc!=SQLITE_DONE);
    }
  }

  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3PagerFilename(Pager *pPager){
................................................................................
int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
  PgHdr *pPgOld;               /* The page being overwritten. */
  Pgno needSyncPgno = 0;       /* Old value of pPg->pgno, if sync is required */
  int rc;                      /* Return code */
  Pgno origPgno;               /* The original page number */

  assert( pPg->nRef>0 );
  assert( pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );

  /* In order to be able to rollback, an in-memory database must journal
  ** the page we are moving from.
  */
  if( MEMDB ){
    rc = sqlite3PagerWrite(pPg);
    if( rc ) return rc;
................................................................................
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( pageInJournal(pPg) || pPg->pgno>pPager->dbOrigSize );
    assert( pPg->flags&PGHDR_DIRTY );

  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PGHDR_NEED_SYNC flag was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.
  */
  pPg->flags &= ~PGHDR_NEED_SYNC;
  pPgOld = pager_lookup(pPager, pgno);
  assert( !pPgOld || pPgOld->nRef==1 );
  if( pPgOld ){
    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
    if( MEMDB ){
      /* Do not discard pages from an in-memory database since we might
      ** need to rollback later.  Just move the page out of the way. */

      sqlite3PcacheMove(pPgOld, pPager->dbSize+1);
    }else{
      sqlite3PcacheDrop(pPgOld);
    }
  }

  origPgno = pPg->pgno;
  sqlite3PcacheMove(pPg, pgno);
  sqlite3PcacheMakeDirty(pPg);


  /* For an in-memory database, make sure the original page continues
  ** to exist, in case the transaction needs to roll back.  Use pPgOld
  ** as the original page since it has already been allocated.
  */
  if( MEMDB ){
    assert( pPgOld );
    sqlite3PcacheMove(pPgOld, origPgno);
    sqlite3PagerUnref(pPgOld);
  }

  if( needSyncPgno ){
    /* If needSyncPgno is non-zero, then the journal file needs to be 
    ** sync()ed before any data is written to database file page needSyncPgno.
    ** Currently, no such page exists in the page-cache and the 
    ** "is journaled" bitvec flag has been set. This needs to be remedied by
    ** loading the page into the pager-cache and setting the PGHDR_NEED_SYNC
    ** flag.
    **
    ** If the attempt to load the page into the page-cache fails, (due
    ** to a malloc() or IO failure), clear the bit in the pInJournal[]
    ** array. Otherwise, if the page is loaded and written again in
    ** this transaction, it may be written to the database file before
    ** it is synced into the journal file. This way, it may end up in
    ** the journal file twice, but that is not a problem.



    */
    PgHdr *pPgHdr;

    rc = sqlite3PagerGet(pPager, needSyncPgno, &pPgHdr);
    if( rc!=SQLITE_OK ){
      if( needSyncPgno<=pPager->dbOrigSize ){
        assert( pPager->pTmpSpace!=0 );
        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno, pPager->pTmpSpace);
      }
      return rc;
    }


    pPgHdr->flags |= PGHDR_NEED_SYNC;
    sqlite3PcacheMakeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }











  return SQLITE_OK;
}
#endif

/*
** Return a pointer to the data for the specified page.
*/
................................................................................
    assert( eOld==PAGER_JOURNALMODE_MEMORY || eOld==PAGER_JOURNALMODE_OFF );
    if( eMode!=PAGER_JOURNALMODE_MEMORY && eMode!=PAGER_JOURNALMODE_OFF ){
      eMode = eOld;
    }
  }

  if( eMode!=eOld ){









    /* Change the journal mode. */
    assert( pPager->eState!=PAGER_ERROR );
    pPager->journalMode = (u8)eMode;

    /* When transistioning from TRUNCATE or PERSIST to any other journal
    ** mode except WAL, unless the pager is in locking_mode=exclusive mode,
    ** delete the journal file.
    */
    assert( (PAGER_JOURNALMODE_TRUNCATE & 5)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST & 5)==1 );
    assert( (PAGER_JOURNALMODE_DELETE & 5)==0 );
    assert( (PAGER_JOURNALMODE_MEMORY & 5)==4 );
    assert( (PAGER_JOURNALMODE_OFF & 5)==0 );
................................................................................
      ** not possible, then that is not a problem. Deleting the journal file
      ** here is an optimization only.
      **
      ** Before deleting the journal file, obtain a RESERVED lock on the
      ** database file. This ensures that the journal file is not deleted
      ** while it is in use by some other client.
      */
      sqlite3OsClose(pPager->jfd);
      if( pPager->eLock>=RESERVED_LOCK ){
        sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }else{
        int rc = SQLITE_OK;
        int state = pPager->eState;
        if( state==PAGER_OPEN ){
          rc = sqlite3PagerSharedLock(pPager);
        }

        if( pPager->eState==PAGER_READER ){
          assert( rc==SQLITE_OK );
          rc = pagerLockDb(pPager, RESERVED_LOCK);
        }
        if( rc==SQLITE_OK ){
          sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
        }
        if( rc==SQLITE_OK && state==PAGER_READER ){
          pagerUnlockDb(pPager, SHARED_LOCK);
        }else if( state==PAGER_OPEN ){
          pager_unlock(pPager);
        }
        assert( state==pPager->eState );
      }
    }
  }

  /* Return the new journal mode */
  return (int)pPager->journalMode;
}

................................................................................

/*
** Return TRUE if the pager is in a state where it is OK to change the
** journalmode.  Journalmode changes can only happen when the database
** is unmodified.
*/
int sqlite3PagerOkToChangeJournalMode(Pager *pPager){
  assert( assert_pager_state(pPager) );
  if( pPager->eState>=PAGER_WRITER_CACHEMOD ) return 0;
  if( NEVER(isOpen(pPager->jfd) && pPager->journalOff>0) ) return 0;
  return 1;
}

/*
** Get/set the size-limit used for persistent journal files.
**
................................................................................
** The caller must be holding a SHARED lock on the database file to call
** this function.
**
** If the pager passed as the first argument is open on a real database
** file (not a temp file or an in-memory database), and the WAL file
** is not already open, make an attempt to open it now. If successful,
** return SQLITE_OK. If an error occurs or the VFS used by the pager does 
** not support the xShmXXX() methods, return an error code. *pbOpen is
** not modified in either case.
**
** If the pager is open on a temp-file (or in-memory database), or if
** the WAL file is already open, set *pbOpen to 1 and return SQLITE_OK
** without doing anything.
*/
int sqlite3PagerOpenWal(
  Pager *pPager,                  /* Pager object */
  int *pbOpen                     /* OUT: Set to true if call is a no-op */
){
  int rc = SQLITE_OK;             /* Return code */

  assert( assert_pager_state(pPager) );
  assert( pPager->eState==PAGER_OPEN   || pbOpen );
  assert( pPager->eState==PAGER_READER || !pbOpen );
  assert( pbOpen==0 || *pbOpen==0 );
  assert( pbOpen!=0 || (!pPager->tempFile && !pPager->pWal) );

  if( !pPager->tempFile && !pPager->pWal ){
    if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;

    if( isOpen(pPager->jfd) ){
      sqlite3OsClose(pPager->jfd);
    }

    /* Open the connection to the log file. If this operation fails, 
    ** (e.g. due to malloc() failure), unlock the database file and 
    ** return an error code.
    */
    rc = sqlite3WalOpen(pPager->pVfs, pPager->fd, pPager->zWal, &pPager->pWal);
    if( rc==SQLITE_OK ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;
      pPager->eState = PAGER_OPEN;
    }
  }else{
    *pbOpen = 1;
  }

  return rc;
}

/*
** This function is called to close the connection to the log file prior
................................................................................

  /* If the log file is not already open, but does exist in the file-system,
  ** it may need to be checkpointed before the connection can switch to
  ** rollback mode. Open it now so this can happen.
  */
  if( !pPager->pWal ){
    int logexists = 0;
    rc = pagerLockDb(pPager, SHARED_LOCK);
    if( rc==SQLITE_OK ){
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &logexists
      );
    }
    if( rc==SQLITE_OK && logexists ){
      rc = sqlite3WalOpen(pPager->pVfs, pPager->fd,
................................................................................
    }
  }
    
  /* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
  ** the database file, the log and log-summary files will be deleted.
  */
  if( rc==SQLITE_OK && pPager->pWal ){
    rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal,
                           (pPager->noSync ? 0 : pPager->sync_flags), 
        pPager->pageSize, (u8*)pPager->pTmpSpace
      );
      pPager->pWal = 0;
    }else{
      /* If we cannot get an EXCLUSIVE lock, downgrade the PENDING lock
      ** that we did get back to SHARED. */
      pagerUnlockDb(pPager, SQLITE_LOCK_SHARED);
    }
  }
  return rc;
}

#ifdef SQLITE_HAS_CODEC
/*

Changes to src/sqlite.h.in.

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692








693
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698

699
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**
** The [SQLITE_FCNTL_SIZE_HINT] opcode is used by SQLite to give the VFS
** layer a hint of how large the database file will grow to be during the
** current transaction.  This hint is not guaranteed to be accurate but it
** is often close.  The underlying VFS might choose to preallocate database
** file space based on this hint in order to help writes to the database
** file run faster.








*/
#define SQLITE_FCNTL_LOCKSTATE        1
#define SQLITE_GET_LOCKPROXYFILE      2
#define SQLITE_SET_LOCKPROXYFILE      3
#define SQLITE_LAST_ERRNO             4
#define SQLITE_FCNTL_SIZE_HINT        5


/*
** CAPI3REF: Mutex Handle
**
** The mutex module within SQLite defines [sqlite3_mutex] to be an
** abstract type for a mutex object.  The SQLite core never looks
** at the internal representation of an [sqlite3_mutex].  It only







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**
** The [SQLITE_FCNTL_SIZE_HINT] opcode is used by SQLite to give the VFS
** layer a hint of how large the database file will grow to be during the
** current transaction.  This hint is not guaranteed to be accurate but it
** is often close.  The underlying VFS might choose to preallocate database
** file space based on this hint in order to help writes to the database
** file run faster.
**
** The [SQLITE_FCNTL_CHUNK_SIZE] opcode is used to request that the VFS
** extends and truncates the database file in chunks of a size specified
** by the user. The fourth argument to [sqlite3_file_control()] should 
** point to an integer (type int) containing the new chunk-size to use
** for the nominated database. Allocating database file space in large
** chunks (say 1MB at a time), may reduce file-system fragmentation and
** improve performance on some systems.
*/
#define SQLITE_FCNTL_LOCKSTATE        1
#define SQLITE_GET_LOCKPROXYFILE      2
#define SQLITE_SET_LOCKPROXYFILE      3
#define SQLITE_LAST_ERRNO             4
#define SQLITE_FCNTL_SIZE_HINT        5
#define SQLITE_FCNTL_CHUNK_SIZE       6

/*
** CAPI3REF: Mutex Handle
**
** The mutex module within SQLite defines [sqlite3_mutex] to be an
** abstract type for a mutex object.  The SQLite core never looks
** at the internal representation of an [sqlite3_mutex].  It only

Changes to src/test1.c.

4608
4609
4610
4611
4612
4613
4614






































4615
4616
4617
4618
4619
4620
4621
....
5102
5103
5104
5105
5106
5107
5108

5109
5110
5111
5112
5113
5114
5115
  if( iArg!=0 ) {
    Tcl_AppendResult(interp, "Unexpected non-zero errno: ",
                     Tcl_GetStringFromObj(Tcl_NewIntObj(iArg), 0), " ", 0);
    return TCL_ERROR;
  }
  return TCL_OK;  
}







































/*
** tclcmd:   file_control_lockproxy_test DB PWD
**
** This TCL command runs the sqlite3_file_control interface and
** verifies correct operation of the SQLITE_GET_LOCKPROXYFILE and
** SQLITE_SET_LOCKPROXYFILE verbs.
................................................................................
     { "vfs_unlink_test",            vfs_unlink_test,     0   },
     { "vfs_initfail_test",          vfs_initfail_test,   0   },
     { "vfs_unregister_all",         vfs_unregister_all,  0   },
     { "vfs_reregister_all",         vfs_reregister_all,  0   },
     { "file_control_test",          file_control_test,   0   },
     { "file_control_lasterrno_test", file_control_lasterrno_test,  0   },
     { "file_control_lockproxy_test", file_control_lockproxy_test,  0   },

     { "sqlite3_vfs_list",           vfs_list,     0   },

     /* Functions from os.h */
#ifndef SQLITE_OMIT_UTF16
     { "add_test_collate",        test_collate, 0            },
     { "add_test_collate_needed", test_collate_needed, 0     },
     { "add_test_function",       test_function, 0           },







>
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>







4608
4609
4610
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4622
4623
4624
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4659
....
5140
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5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
  if( iArg!=0 ) {
    Tcl_AppendResult(interp, "Unexpected non-zero errno: ",
                     Tcl_GetStringFromObj(Tcl_NewIntObj(iArg), 0), " ", 0);
    return TCL_ERROR;
  }
  return TCL_OK;  
}

/*
** tclcmd:   file_control_chunksize_test DB DBNAME SIZE
**
** This TCL command runs the sqlite3_file_control interface and
** verifies correct operation of the SQLITE_GET_LOCKPROXYFILE and
** SQLITE_SET_LOCKPROXYFILE verbs.
*/
static int file_control_chunksize_test(
  ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int objc,              /* Number of arguments */
  Tcl_Obj *CONST objv[]  /* Command arguments */
){
  int nSize;                      /* New chunk size */
  char *zDb;                      /* Db name ("main", "temp" etc.) */
  sqlite3 *db;                    /* Database handle */
  int rc;                         /* file_control() return code */

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME SIZE");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) 
   || Tcl_GetIntFromObj(interp, objv[3], &nSize)
  ){
   return TCL_ERROR;
  }
  zDb = Tcl_GetString(objv[2]);
  if( zDb[0]=='\0' ) zDb = NULL;

  rc = sqlite3_file_control(db, zDb, SQLITE_FCNTL_CHUNK_SIZE, (void *)&nSize);
  if( rc ){
    Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_STATIC);
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** tclcmd:   file_control_lockproxy_test DB PWD
**
** This TCL command runs the sqlite3_file_control interface and
** verifies correct operation of the SQLITE_GET_LOCKPROXYFILE and
** SQLITE_SET_LOCKPROXYFILE verbs.
................................................................................
     { "vfs_unlink_test",            vfs_unlink_test,     0   },
     { "vfs_initfail_test",          vfs_initfail_test,   0   },
     { "vfs_unregister_all",         vfs_unregister_all,  0   },
     { "vfs_reregister_all",         vfs_reregister_all,  0   },
     { "file_control_test",          file_control_test,   0   },
     { "file_control_lasterrno_test", file_control_lasterrno_test,  0   },
     { "file_control_lockproxy_test", file_control_lockproxy_test,  0   },
     { "file_control_chunksize_test", file_control_chunksize_test,  0   },
     { "sqlite3_vfs_list",           vfs_list,     0   },

     /* Functions from os.h */
#ifndef SQLITE_OMIT_UTF16
     { "add_test_collate",        test_collate, 0            },
     { "add_test_collate_needed", test_collate_needed, 0     },
     { "add_test_function",       test_function, 0           },

Changes to src/test_journal.c.

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** the first journal-header is written to the journal file.
*/
static int openTransaction(jt_file *pMain, jt_file *pJournal){
  unsigned char *aData;
  sqlite3_file *p = pMain->pReal;
  int rc = SQLITE_OK;


  aData = sqlite3_malloc(pMain->nPagesize);
  pMain->pWritable = sqlite3BitvecCreate(pMain->nPage);
  pMain->aCksum = sqlite3_malloc(sizeof(u32) * (pMain->nPage + 1));
  pJournal->iMaxOff = 0;

  if( !pMain->pWritable || !pMain->aCksum || !aData ){
    rc = SQLITE_IOERR_NOMEM;
................................................................................

    stop_ioerr_simulation(&iSave, &iSave2);

    /* Read the database free-list. Add the page-number for each free-list
    ** leaf to the jt_file.pWritable bitvec.
    */
    rc = sqlite3OsRead(p, aData, pMain->nPagesize, 0);









    iTrunk = decodeUint32(&aData[32]);
    while( rc==SQLITE_OK && iTrunk>0 ){
      u32 nLeaf;
      u32 iLeaf;
      sqlite3_int64 iOff = (iTrunk-1)*pMain->nPagesize;
      rc = sqlite3OsRead(p, aData, pMain->nPagesize, iOff);
      nLeaf = decodeUint32(&aData[4]);
................................................................................
  start_ioerr_simulation(iSave, iSave2);
  sqlite3_free(aPage);
  if( rc==SQLITE_IOERR_SHORT_READ ){
    rc = SQLITE_OK;
  }
  return rc;
}


/*
** Write data to an jt-file.
*/
static int jtWrite(
  sqlite3_file *pFile, 
  const void *zBuf, 







>







 







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504
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508
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510
** the first journal-header is written to the journal file.
*/
static int openTransaction(jt_file *pMain, jt_file *pJournal){
  unsigned char *aData;
  sqlite3_file *p = pMain->pReal;
  int rc = SQLITE_OK;

  closeTransaction(pMain);
  aData = sqlite3_malloc(pMain->nPagesize);
  pMain->pWritable = sqlite3BitvecCreate(pMain->nPage);
  pMain->aCksum = sqlite3_malloc(sizeof(u32) * (pMain->nPage + 1));
  pJournal->iMaxOff = 0;

  if( !pMain->pWritable || !pMain->aCksum || !aData ){
    rc = SQLITE_IOERR_NOMEM;
................................................................................

    stop_ioerr_simulation(&iSave, &iSave2);

    /* Read the database free-list. Add the page-number for each free-list
    ** leaf to the jt_file.pWritable bitvec.
    */
    rc = sqlite3OsRead(p, aData, pMain->nPagesize, 0);
    if( rc==SQLITE_OK ){
      u32 nDbsize = decodeUint32(&aData[28]);
      if( nDbsize>0 && memcmp(&aData[24], &aData[92], 4)==0 ){
        u32 iPg;
        for(iPg=nDbsize+1; iPg<=pMain->nPage; iPg++){
          sqlite3BitvecSet(pMain->pWritable, iPg);
        }
      }
    }
    iTrunk = decodeUint32(&aData[32]);
    while( rc==SQLITE_OK && iTrunk>0 ){
      u32 nLeaf;
      u32 iLeaf;
      sqlite3_int64 iOff = (iTrunk-1)*pMain->nPagesize;
      rc = sqlite3OsRead(p, aData, pMain->nPagesize, iOff);
      nLeaf = decodeUint32(&aData[4]);
................................................................................
  start_ioerr_simulation(iSave, iSave2);
  sqlite3_free(aPage);
  if( rc==SQLITE_IOERR_SHORT_READ ){
    rc = SQLITE_OK;
  }
  return rc;
}


/*
** Write data to an jt-file.
*/
static int jtWrite(
  sqlite3_file *pFile, 
  const void *zBuf, 

Changes to src/test_malloc.c.

724
725
726
727
728
729
730
731



732
733
734
735
736
737
738
...
741
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750
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814
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838
839
840
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842
843
844
845
846
847
848
849
850
851
852
    extern int sqlite3MemdebugSettitle(const char*);
    sqlite3MemdebugSettitle(zTitle);
  }
#endif
  return TCL_OK;
}

#define MALLOC_LOG_FRAMES 10 



static Tcl_HashTable aMallocLog;
static int mallocLogEnabled = 0;

typedef struct MallocLog MallocLog;
struct MallocLog {
  int nCall;
  int nByte;
................................................................................
#ifdef SQLITE_MEMDEBUG
static void test_memdebug_callback(int nByte, int nFrame, void **aFrame){
  if( mallocLogEnabled ){
    MallocLog *pLog;
    Tcl_HashEntry *pEntry;
    int isNew;

    int aKey[MALLOC_LOG_FRAMES];
    int nKey = sizeof(int)*MALLOC_LOG_FRAMES;

    memset(aKey, 0, nKey);
    if( (sizeof(void*)*nFrame)<nKey ){
      nKey = nFrame*sizeof(void*);
    }
    memcpy(aKey, aFrame, nKey);

................................................................................
    pEntry;
    pEntry=Tcl_NextHashEntry(&search)
  ){
    MallocLog *pLog = (MallocLog *)Tcl_GetHashValue(pEntry);
    Tcl_Free((char *)pLog);
  }
  Tcl_DeleteHashTable(&aMallocLog);
  Tcl_InitHashTable(&aMallocLog, MALLOC_LOG_FRAMES);
}

static int test_memdebug_log(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
................................................................................

  if( !isInit ){
#ifdef SQLITE_MEMDEBUG
    extern void sqlite3MemdebugBacktraceCallback(
        void (*xBacktrace)(int, int, void **));
    sqlite3MemdebugBacktraceCallback(test_memdebug_callback);
#endif
    Tcl_InitHashTable(&aMallocLog, MALLOC_LOG_FRAMES);
    isInit = 1;
  }

  if( objc<2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "SUB-COMMAND ...");
  }
  if( Tcl_GetIndexFromObj(interp, objv[1], MB_strs, "sub-command", 0, &iSub) ){
................................................................................
      mallocLogEnabled = 0;
      break;
    case MB_LOG_DUMP: {
      Tcl_HashSearch search;
      Tcl_HashEntry *pEntry;
      Tcl_Obj *pRet = Tcl_NewObj();

      assert(sizeof(int)==sizeof(void*));

      for(
        pEntry=Tcl_FirstHashEntry(&aMallocLog, &search);
        pEntry;
        pEntry=Tcl_NextHashEntry(&search)
      ){
        Tcl_Obj *apElem[MALLOC_LOG_FRAMES+2];
        MallocLog *pLog = (MallocLog *)Tcl_GetHashValue(pEntry);
        int *aKey = (int *)Tcl_GetHashKey(&aMallocLog, pEntry);
        int ii;
  
        apElem[0] = Tcl_NewIntObj(pLog->nCall);
        apElem[1] = Tcl_NewIntObj(pLog->nByte);
        for(ii=0; ii<MALLOC_LOG_FRAMES; ii++){
          apElem[ii+2] = Tcl_NewIntObj(aKey[ii]);
        }

        Tcl_ListObjAppendElement(interp, pRet,
            Tcl_NewListObj(MALLOC_LOG_FRAMES+2, apElem)
        );
      }








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...
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...
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809
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811
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813
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816
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...
826
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833
834
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841
842
843
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845
846
847
848
849
850
851
852
853
854
855
    extern int sqlite3MemdebugSettitle(const char*);
    sqlite3MemdebugSettitle(zTitle);
  }
#endif
  return TCL_OK;
}

#define MALLOC_LOG_FRAMES  10 
#define MALLOC_LOG_KEYINTS (                                              \
    10 * ((sizeof(int)>=sizeof(void*)) ? 1 : sizeof(void*)/sizeof(int))   \
)
static Tcl_HashTable aMallocLog;
static int mallocLogEnabled = 0;

typedef struct MallocLog MallocLog;
struct MallocLog {
  int nCall;
  int nByte;
................................................................................
#ifdef SQLITE_MEMDEBUG
static void test_memdebug_callback(int nByte, int nFrame, void **aFrame){
  if( mallocLogEnabled ){
    MallocLog *pLog;
    Tcl_HashEntry *pEntry;
    int isNew;

    int aKey[MALLOC_LOG_KEYINTS];
    int nKey = sizeof(int)*MALLOC_LOG_KEYINTS;

    memset(aKey, 0, nKey);
    if( (sizeof(void*)*nFrame)<nKey ){
      nKey = nFrame*sizeof(void*);
    }
    memcpy(aKey, aFrame, nKey);

................................................................................
    pEntry;
    pEntry=Tcl_NextHashEntry(&search)
  ){
    MallocLog *pLog = (MallocLog *)Tcl_GetHashValue(pEntry);
    Tcl_Free((char *)pLog);
  }
  Tcl_DeleteHashTable(&aMallocLog);
  Tcl_InitHashTable(&aMallocLog, MALLOC_LOG_KEYINTS);
}

static int test_memdebug_log(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
................................................................................

  if( !isInit ){
#ifdef SQLITE_MEMDEBUG
    extern void sqlite3MemdebugBacktraceCallback(
        void (*xBacktrace)(int, int, void **));
    sqlite3MemdebugBacktraceCallback(test_memdebug_callback);
#endif
    Tcl_InitHashTable(&aMallocLog, MALLOC_LOG_KEYINTS);
    isInit = 1;
  }

  if( objc<2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "SUB-COMMAND ...");
  }
  if( Tcl_GetIndexFromObj(interp, objv[1], MB_strs, "sub-command", 0, &iSub) ){
................................................................................
      mallocLogEnabled = 0;
      break;
    case MB_LOG_DUMP: {
      Tcl_HashSearch search;
      Tcl_HashEntry *pEntry;
      Tcl_Obj *pRet = Tcl_NewObj();

      assert(sizeof(Tcl_WideInt)>=sizeof(void*));

      for(
        pEntry=Tcl_FirstHashEntry(&aMallocLog, &search);
        pEntry;
        pEntry=Tcl_NextHashEntry(&search)
      ){
        Tcl_Obj *apElem[MALLOC_LOG_FRAMES+2];
        MallocLog *pLog = (MallocLog *)Tcl_GetHashValue(pEntry);
        Tcl_WideInt *aKey = (Tcl_WideInt *)Tcl_GetHashKey(&aMallocLog, pEntry);
        int ii;
  
        apElem[0] = Tcl_NewIntObj(pLog->nCall);
        apElem[1] = Tcl_NewIntObj(pLog->nByte);
        for(ii=0; ii<MALLOC_LOG_FRAMES; ii++){
          apElem[ii+2] = Tcl_NewWideIntObj(aKey[ii]);
        }

        Tcl_ListObjAppendElement(interp, pRet,
            Tcl_NewListObj(MALLOC_LOG_FRAMES+2, apElem)
        );
      }

Changes to src/test_stat.c.

372
373
374
375
376
377
378

379





380
381
382
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384
385
386
...
482
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496
497
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501
502
503
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  sqlite3_free(pCsr->zPath);
  pCsr->zPath = 0;

  if( pCsr->aPage[0].pPg==0 ){
    rc = sqlite3_step(pCsr->pStmt);
    if( rc==SQLITE_ROW ){

      u32 iRoot = sqlite3_column_int64(pCsr->pStmt, 1);





      rc = sqlite3PagerGet(pPager, iRoot, &pCsr->aPage[0].pPg);
      pCsr->aPage[0].iPgno = iRoot;
      pCsr->aPage[0].iCell = 0;
      pCsr->aPage[0].zPath = sqlite3_mprintf("/");
      pCsr->iPage = 0;
    }else{
      pCsr->isEof = 1;
................................................................................
}

static int statFilter(
  sqlite3_vtab_cursor *pCursor, 
  int idxNum, const char *idxStr,
  int argc, sqlite3_value **argv
){
  sqlite3 *db = ((StatTable *)(pCursor->pVtab))->db;
  StatCursor *pCsr = (StatCursor *)pCursor;
  int nPage = 0;

  statResetCsr((StatCursor *)pCursor);
  sqlite3PagerPagecount(sqlite3BtreePager(db->aDb[0].pBt), &nPage);
  if( nPage==0 ){
    pCsr->isEof = 1;
    return SQLITE_OK;
  }

  return statNext(pCursor);
}

static int statColumn(
  sqlite3_vtab_cursor *pCursor, 
  sqlite3_context *ctx, 
  int i







>

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495

496
497






498
499
500
501
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504

  sqlite3_free(pCsr->zPath);
  pCsr->zPath = 0;

  if( pCsr->aPage[0].pPg==0 ){
    rc = sqlite3_step(pCsr->pStmt);
    if( rc==SQLITE_ROW ){
      int nPage;
      u32 iRoot = sqlite3_column_int64(pCsr->pStmt, 1);
      sqlite3PagerPagecount(pPager, &nPage);
      if( nPage==0 ){
        pCsr->isEof = 1;
        return sqlite3_reset(pCsr->pStmt);
      }
      rc = sqlite3PagerGet(pPager, iRoot, &pCsr->aPage[0].pPg);
      pCsr->aPage[0].iPgno = iRoot;
      pCsr->aPage[0].iCell = 0;
      pCsr->aPage[0].zPath = sqlite3_mprintf("/");
      pCsr->iPage = 0;
    }else{
      pCsr->isEof = 1;
................................................................................
}

static int statFilter(
  sqlite3_vtab_cursor *pCursor, 
  int idxNum, const char *idxStr,
  int argc, sqlite3_value **argv
){

  StatCursor *pCsr = (StatCursor *)pCursor;


  statResetCsr((StatCursor *)pCursor);






  return statNext(pCursor);
}

static int statColumn(
  sqlite3_vtab_cursor *pCursor, 
  sqlite3_context *ctx, 
  int i

Changes to src/wal.c.

1517
1518
1519
1520
1521
1522
1523

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1526
1527
1528
1529
1530
....
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1553
1554
....
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1573











1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
....
2027
2028
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2032
2033

2034
2035
2036
2037
2038
2039
2040
....
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2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160


2161
2162
2163
2164
2165
2166
2167
){
  int rc;                         /* Return code */
  int szPage = pWal->hdr.szPage;  /* Database page-size */
  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */

  int i;                          /* Loop counter */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  if( pWal->hdr.mxFrame==0 ) return SQLITE_OK;

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
................................................................................

  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  mxSafeFrame = pWal->hdr.mxFrame;

  pInfo = walCkptInfo(pWal);
  for(i=1; i<WAL_NREADER; i++){
    u32 y = pInfo->aReadMark[i];
    if( mxSafeFrame>=y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
................................................................................
      }
    }
  }

  if( pInfo->nBackfill<mxSafeFrame
   && (rc = walLockExclusive(pWal, WAL_READ_LOCK(0), 1))==SQLITE_OK
  ){

    u32 nBackfill = pInfo->nBackfill;

    /* Sync the WAL to disk */
    if( sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
    }












    /* Iterate through the contents of the WAL, copying data to the db file. */
    while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
      i64 iOffset;
      assert( walFramePgno(pWal, iFrame)==iDbpage );
      if( iFrame<=nBackfill || iFrame>mxSafeFrame ) continue;
      iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE;
      /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
      rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset);
      if( rc!=SQLITE_OK ) break;
      iOffset = (iDbpage-1)*(i64)szPage;
      testcase( IS_BIG_INT(iOffset) );
      rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset);
................................................................................
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
void sqlite3WalEndReadTransaction(Wal *pWal){

  if( pWal->readLock>=0 ){
    walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
    pWal->readLock = -1;
  }
}

/*
................................................................................

  *pInWal = 0;
  return SQLITE_OK;
}


/* 
** Set *pPgno to the size of the database file (or zero, if unknown).
*/
void sqlite3WalDbsize(Wal *pWal, Pgno *pPgno){
  assert( pWal->readLock>=0 || pWal->lockError );
  *pPgno = pWal->hdr.nPage;


}


/* 
** This function starts a write transaction on the WAL.
**
** A read transaction must have already been started by a prior call







>







 







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>







1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
....
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
....
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
....
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
....
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
){
  int rc;                         /* Return code */
  int szPage = pWal->hdr.szPage;  /* Database page-size */
  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  u32 mxPage;                     /* Max database page to write */
  int i;                          /* Loop counter */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  if( pWal->hdr.mxFrame==0 ) return SQLITE_OK;

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
................................................................................

  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  mxSafeFrame = pWal->hdr.mxFrame;
  mxPage = pWal->hdr.nPage;
  pInfo = walCkptInfo(pWal);
  for(i=1; i<WAL_NREADER; i++){
    u32 y = pInfo->aReadMark[i];
    if( mxSafeFrame>=y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
................................................................................
      }
    }
  }

  if( pInfo->nBackfill<mxSafeFrame
   && (rc = walLockExclusive(pWal, WAL_READ_LOCK(0), 1))==SQLITE_OK
  ){
    i64 nSize;                    /* Current size of database file */
    u32 nBackfill = pInfo->nBackfill;

    /* Sync the WAL to disk */
    if( sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
    }

    /* If the database file may grow as a result of this checkpoint, hint
    ** about the eventual size of the db file to the VFS layer. 
    */
    if( rc==SQLITE_OK ){
      i64 nReq = ((i64)mxPage * szPage);
      rc = sqlite3OsFileSize(pWal->pDbFd, &nSize);
      if( rc==SQLITE_OK && nSize<nReq ){
        sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq);
      }
    }

    /* Iterate through the contents of the WAL, copying data to the db file. */
    while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
      i64 iOffset;
      assert( walFramePgno(pWal, iFrame)==iDbpage );
      if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ) continue;
      iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE;
      /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
      rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset);
      if( rc!=SQLITE_OK ) break;
      iOffset = (iDbpage-1)*(i64)szPage;
      testcase( IS_BIG_INT(iOffset) );
      rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset);
................................................................................
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
void sqlite3WalEndReadTransaction(Wal *pWal){
  sqlite3WalEndWriteTransaction(pWal);
  if( pWal->readLock>=0 ){
    walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
    pWal->readLock = -1;
  }
}

/*
................................................................................

  *pInWal = 0;
  return SQLITE_OK;
}


/* 
** Return the size of the database in pages (or zero, if unknown).
*/
Pgno sqlite3WalDbsize(Wal *pWal){
  if( pWal && pWal->readLock>=0 ){
    return pWal->hdr.nPage;
  }
  return 0;
}


/* 
** This function starts a write transaction on the WAL.
**
** A read transaction must have already been started by a prior call

Changes to src/wal.h.

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#ifdef SQLITE_OMIT_WAL
# define sqlite3WalOpen(x,y,z)                 0
# define sqlite3WalClose(w,x,y,z)              0
# define sqlite3WalBeginReadTransaction(y,z)   0
# define sqlite3WalEndReadTransaction(z)
# define sqlite3WalRead(v,w,x,y,z)             0
# define sqlite3WalDbsize(y,z)
# define sqlite3WalBeginWriteTransaction(y)    0
# define sqlite3WalEndWriteTransaction(x)      0
# define sqlite3WalUndo(x,y,z)                 0
# define sqlite3WalSavepoint(y,z)
# define sqlite3WalSavepointUndo(y,z)          0
# define sqlite3WalFrames(u,v,w,x,y,z)         0
# define sqlite3WalCheckpoint(u,v,w,x)         0
................................................................................
*/
int sqlite3WalBeginReadTransaction(Wal *pWal, int *);
void sqlite3WalEndReadTransaction(Wal *pWal);

/* Read a page from the write-ahead log, if it is present. */
int sqlite3WalRead(Wal *pWal, Pgno pgno, int *pInWal, int nOut, u8 *pOut);

/* Return the size of the database as it existed at the beginning
** of the snapshot */
void sqlite3WalDbsize(Wal *pWal, Pgno *pPgno);

/* Obtain or release the WRITER lock. */
int sqlite3WalBeginWriteTransaction(Wal *pWal);
int sqlite3WalEndWriteTransaction(Wal *pWal);

/* Undo any frames written (but not committed) to the log */
int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx);







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#ifdef SQLITE_OMIT_WAL
# define sqlite3WalOpen(x,y,z)                 0
# define sqlite3WalClose(w,x,y,z)              0
# define sqlite3WalBeginReadTransaction(y,z)   0
# define sqlite3WalEndReadTransaction(z)
# define sqlite3WalRead(v,w,x,y,z)             0
# define sqlite3WalDbsize(y)                   0
# define sqlite3WalBeginWriteTransaction(y)    0
# define sqlite3WalEndWriteTransaction(x)      0
# define sqlite3WalUndo(x,y,z)                 0
# define sqlite3WalSavepoint(y,z)
# define sqlite3WalSavepointUndo(y,z)          0
# define sqlite3WalFrames(u,v,w,x,y,z)         0
# define sqlite3WalCheckpoint(u,v,w,x)         0
................................................................................
*/
int sqlite3WalBeginReadTransaction(Wal *pWal, int *);
void sqlite3WalEndReadTransaction(Wal *pWal);

/* Read a page from the write-ahead log, if it is present. */
int sqlite3WalRead(Wal *pWal, Pgno pgno, int *pInWal, int nOut, u8 *pOut);

/* If the WAL is not empty, return the size of the database. */

Pgno sqlite3WalDbsize(Wal *pWal);

/* Obtain or release the WRITER lock. */
int sqlite3WalBeginWriteTransaction(Wal *pWal);
int sqlite3WalEndWriteTransaction(Wal *pWal);

/* Undo any frames written (but not committed) to the log */
int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx);

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  sqlite3_expired $S
} {1}
do_test analyze3-3.6.5 {
  sqlite3_finalize $S
} {SQLITE_OK}

do_test analyze3-3.7.1 {
breakpoint
  set S [sqlite3_prepare_v2 db {
    SELECT * FROM t1 WHERE a IN (
      ?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?33,
      ?11, ?12, ?13, ?14, ?15, ?16, ?17, ?18, ?19, ?20,
      ?21, ?22, ?23, ?24, ?25, ?26, ?27, ?28, ?29, ?30, ?31, ?32
    ) AND b>?10;
  } -1 dummy]







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  sqlite3_expired $S
} {1}
do_test analyze3-3.6.5 {
  sqlite3_finalize $S
} {SQLITE_OK}

do_test analyze3-3.7.1 {

  set S [sqlite3_prepare_v2 db {
    SELECT * FROM t1 WHERE a IN (
      ?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?33,
      ?11, ?12, ?13, ?14, ?15, ?16, ?17, ?18, ?19, ?20,
      ?21, ?22, ?23, ?24, ?25, ?26, ?27, ?28, ?29, ?30, ?31, ?32
    ) AND b>?10;
  } -1 dummy]

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}

#---------------------------------------------------------------------------
# Run the dbstatus-2 and dbstatus-3 tests with several of different
# lookaside buffer sizes.
#
foreach ::lookaside_buffer_size {0 64 120} {







  #-------------------------------------------------------------------------
  # Tests for SQLITE_DBSTATUS_SCHEMA_USED.
  #
  # Each test in the following block works as follows. Each test uses a
  # different database schema.
  #
................................................................................

    # Tests for which the test name ends in an "x" report slightly less
    # memory than is actually freed when all statements are finalized.
    # This is because a small amount of memory allocated by a virtual table
    # implementation using sqlite3_mprintf() is technically considered
    # external and so is not counted as "statement memory".
    #

    if {[string match *x $tn]} {
      do_test dbstatus-3.$tn.bx { expr $nStmt1<=$nFree }  {1}
    } else {
      do_test dbstatus-3.$tn.b { expr $nStmt1==$nFree } {1}
    }

    do_test dbstatus-3.$tn.c { list $nAlloc1 $nStmt1 } [list $nAlloc3 $nStmt3]
    do_test dbstatus-3.$tn.d { list $nAlloc2 $nStmt2 } [list $nAlloc4 $nStmt4]
  }
}

finish_test







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}

#---------------------------------------------------------------------------
# Run the dbstatus-2 and dbstatus-3 tests with several of different
# lookaside buffer sizes.
#
foreach ::lookaside_buffer_size {0 64 120} {

  # Do not run any of these tests if there is SQL configured to run
  # as part of the [sqlite3] command. This prevents the script from
  # configuring the size of the lookaside buffer after [sqlite3] has
  # returned.
  if {[presql] != ""} break

  #-------------------------------------------------------------------------
  # Tests for SQLITE_DBSTATUS_SCHEMA_USED.
  #
  # Each test in the following block works as follows. Each test uses a
  # different database schema.
  #
................................................................................

    # Tests for which the test name ends in an "x" report slightly less
    # memory than is actually freed when all statements are finalized.
    # This is because a small amount of memory allocated by a virtual table
    # implementation using sqlite3_mprintf() is technically considered
    # external and so is not counted as "statement memory".
    #
puts "$nStmt1 $nFree"
    if {[string match *x $tn]} {
      do_test dbstatus-3.$tn.bx { expr $nStmt1<=$nFree }  {1}
    } else {
      do_test dbstatus-3.$tn.b { expr $nStmt1==$nFree } {1}
    }

    do_test dbstatus-3.$tn.c { list $nAlloc1 $nStmt1 } [list $nAlloc3 $nStmt3]
    do_test dbstatus-3.$tn.d { list $nAlloc2 $nStmt2 } [list $nAlloc4 $nStmt4]
  }
}

finish_test

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# a transaction.
#
# These tests are not run on windows because the windows backend
# opens the journal file for exclusive access, preventing its contents 
# from being inspected externally.
#
if {$tcl_platform(platform) != "windows"} {





  proc filestate {fname} {
    set exists 0
    set content 0
    if {[file exists $fname]} {
      set exists 1
      set hdr [hexio_read $fname 0 28]
      set content [expr {0==[string match $hdr [string repeat 0 56]]}]
    }
    list $exists $content
  }

  do_test exclusive-3.0 {
    filestate test.db-journal
  } {0 0}
  do_test exclusive-3.1 {
    execsql {
      PRAGMA locking_mode = exclusive;
      BEGIN;







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# a transaction.
#
# These tests are not run on windows because the windows backend
# opens the journal file for exclusive access, preventing its contents 
# from being inspected externally.
#
if {$tcl_platform(platform) != "windows"} {

  # Return a list of two booleans (either 0 or 1). The first is true
  # if the named file exists. The second is true only if the file
  # exists and the first 28 bytes contain at least one non-zero byte.
  #
  proc filestate {fname} {
    set exists 0
    set content 0
    if {[file exists $fname]} {
      set exists 1
      set hdr [hexio_read $fname 0 28]
      set content [expr {0==[string match $hdr [string repeat 0 56]]}]
    }
    list $exists $content
  }

  do_test exclusive-3.0 {
    filestate test.db-journal
  } {0 0}
  do_test exclusive-3.1 {
    execsql {
      PRAGMA locking_mode = exclusive;
      BEGIN;

Added test/fallocate.test.





































































































































































































































































































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# 2010 July 28
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

file_control_chunksize_test db main [expr 1024*1024]

do_test fallocate-1.1 {
  execsql {
    PRAGMA page_size = 1024;
    PRAGMA auto_vacuum = 1;
    CREATE TABLE t1(a, b);
  }
  file size test.db
} [expr 1*1024*1024]

do_test fallocate-1.2 {
  execsql { INSERT INTO t1 VALUES(1, zeroblob(1024*900)) }
  file size test.db
} [expr 1*1024*1024]

do_test fallocate-1.3 {
  execsql { INSERT INTO t1 VALUES(2, zeroblob(1024*900)) }
  file size test.db
} [expr 2*1024*1024]

do_test fallocate-1.4 {
  execsql { DELETE FROM t1 WHERE a = 1 }
  file size test.db
} [expr 1*1024*1024]

do_test fallocate-1.5 {
  execsql { DELETE FROM t1 WHERE a = 2 }
  file size test.db
} [expr 1*1024*1024]

do_test fallocate-1.6 {
  execsql { PRAGMA freelist_count }
} {0}

# Start a write-transaction and read the "database file size" field from
# the journal file. This field should be set to the number of pages in
# the database file based on the size of the file on disk, not the actual
# logical size of the database within the file.
#
# We need to check this to verify that if in the unlikely event a rollback
# causes a database file to grow, the database grows to its previous size
# on disk, not to the minimum size required to hold the database image.
#
do_test fallocate-1.7 {
  execsql { BEGIN; INSERT INTO t1 VALUES(1, 2); }
  if {[permutation] != "inmemory_journal"} {
    hexio_get_int [hexio_read test.db-journal 16 4]
  } else {
    set {} 1024
  }
} {1024}
do_test fallocate-1.8 { execsql { COMMIT } } {}


#-------------------------------------------------------------------------
# The following tests - fallocate-2.* - test that things work in WAL
# mode as well.
#
set skipwaltests [expr {
  [permutation]=="journaltest" || [permutation]=="inmemory_journal"
}]
ifcapable !wal { set skipwaltests 1 }

if {!$skipwaltests} {
  db close
  file delete -force test.db
  sqlite3 db test.db
  file_control_chunksize_test db main [expr 32*1024]
  
  do_test fallocate-2.1 {
    execsql {
      PRAGMA page_size = 1024;
      PRAGMA journal_mode = WAL;
      CREATE TABLE t1(a, b);
    }
    file size test.db
  } [expr 32*1024]
  
  do_test fallocate-2.2 {
    execsql { INSERT INTO t1 VALUES(1, zeroblob(35*1024)) }
    execsql { PRAGMA wal_checkpoint }
    file size test.db
  } [expr 64*1024]
  
  do_test fallocate-2.3 {
    execsql { DELETE FROM t1 }
    execsql { VACUUM }
    file size test.db
  } [expr 64*1024]
  
  do_test fallocate-2.4 {
    execsql { PRAGMA wal_checkpoint }
    file size test.db
  } [expr 32*1024]
  
  do_test fallocate-2.5 {
    execsql { 
      INSERT INTO t1 VALUES(2, randomblob(35*1024));
      PRAGMA wal_checkpoint;
      INSERT INTO t1 VALUES(3, randomblob(128));
      DELETE FROM t1 WHERE a = 2;
      VACUUM;
    }
    file size test.db
  } [expr 64*1024]
  
  do_test fallocate-2.6 {
    sqlite3 db2 test.db
    execsql { BEGIN ; SELECT count(a) FROM t1 } db2
    execsql {  
      INSERT INTO t1 VALUES(4, randomblob(128));
      PRAGMA wal_checkpoint;
    }
    file size test.db
  } [expr 64*1024]
  
  do_test fallocate-2.7 {
    execsql { SELECT count(b) FROM t1 } db2
  } {1}
  
  do_test fallocate-2.8 {
    execsql { COMMIT } db2
    execsql { PRAGMA wal_checkpoint }
    file size test.db
  } [expr 32*1024]
}


finish_test

Changes to test/jrnlmode.test.

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      PRAGMA page_size = 1024;
      PRAGMA user_version = 5;
      PRAGMA user_version;
    }
  } {memory 5}
  do_test jrnlmode-7.2 { file size test.db } {1024}
}
































finish_test








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      PRAGMA page_size = 1024;
      PRAGMA user_version = 5;
      PRAGMA user_version;
    }
  } {memory 5}
  do_test jrnlmode-7.2 { file size test.db } {1024}
}

do_execsql_test jrnlmode-8.1  { PRAGMA locking_mode=EXCLUSIVE } {exclusive}
do_execsql_test jrnlmode-8.2  { CREATE TABLE t1(x) }            {}
do_execsql_test jrnlmode-8.3  { INSERT INTO t1 VALUES(123) }    {}
do_execsql_test jrnlmode-8.4  { SELECT * FROM t1 }              {123}
do_execsql_test jrnlmode-8.5  { PRAGMA journal_mode=PERSIST }   {persist}
do_execsql_test jrnlmode-8.6  { PRAGMA journal_mode=DELETE }    {delete}
do_execsql_test jrnlmode-8.7  { PRAGMA journal_mode=TRUNCATE }  {truncate}
do_execsql_test jrnlmode-8.8  { PRAGMA journal_mode=DELETE }    {delete}
do_execsql_test jrnlmode-8.9  { CREATE TABLE t2(y) }            {}
do_execsql_test jrnlmode-8.10 { INSERT INTO t2 VALUES(456) }    {}
do_execsql_test jrnlmode-8.11 { SELECT * FROM t1, t2 }          {123 456}
do_execsql_test jrnlmode-8.12 { PRAGMA locking_mode=NORMAL }    {normal}
do_execsql_test jrnlmode-8.13 { PRAGMA journal_mode=PERSIST }   {persist}
do_execsql_test jrnlmode-8.14 { PRAGMA journal_mode=TRUNCATE }  {truncate}
do_execsql_test jrnlmode-8.15 { PRAGMA journal_mode=PERSIST }   {persist}
do_execsql_test jrnlmode-8.16 { PRAGMA journal_mode=DELETE }    {delete}
do_execsql_test jrnlmode-8.17 { PRAGMA journal_mode=TRUNCATE }  {truncate}
do_execsql_test jrnlmode-8.18 { PRAGMA locking_mode=EXCLUSIVE } {exclusive}
do_execsql_test jrnlmode-8.19 { CREATE TABLE t3(z) }            {}
do_execsql_test jrnlmode-8.20 { BEGIN IMMEDIATE }               {}
do_execsql_test jrnlmode-8.21 { PRAGMA journal_mode=DELETE }    {delete}
do_execsql_test jrnlmode-8.22 { COMMIT }                        {}
do_execsql_test jrnlmode-8.23 { PRAGMA journal_mode=DELETE }    {delete}
do_execsql_test jrnlmode-8.24 { PRAGMA journal_mode=TRUNCATE }  {truncate}
do_execsql_test jrnlmode-8.25 { PRAGMA locking_mode=NORMAL }    {normal}
do_execsql_test jrnlmode-8.26 { CREATE TABLE t4(w) }            {}
do_execsql_test jrnlmode-8.27 { BEGIN IMMEDIATE }               {}
do_execsql_test jrnlmode-8.28 { PRAGMA journal_mode=DELETE }    {delete}
do_execsql_test jrnlmode-8.29 { COMMIT }                        {}
do_execsql_test jrnlmode-8.30 { PRAGMA journal_mode=DELETE }    {delete}

finish_test

Added test/pager3.test.



































































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# 2010 June 15
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
source $testdir/lock_common.tcl
source $testdir/malloc_common.tcl
source $testdir/wal_common.tcl


foreach {tn sql res j} {
  1 "PRAGMA journal_mode = DELETE"  delete        0
  2 "CREATE TABLE t1(a, b)"         {}            0
  3 "PRAGMA locking_mode=EXCLUSIVE" {exclusive}   0
  4 "INSERT INTO t1 VALUES(1, 2)"   {}            1
  5 "PRAGMA locking_mode=NORMAL"    {normal}      1
  6 "SELECT * FROM t1"              {1 2}         0
} {
  do_execsql_test pager3-1.$tn.1 $sql $res
  do_test         pager3-1.$tn.2 { file exists test.db-journal } $j
}


finish_test

Changes to test/permutations.test.

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lappend ::testsuitelist xxx

test_suite "veryquick" -prefix "" -description {
  "Very" quick test suite. Runs in less than 5 minutes on a workstation. 
  This test suite is the same as the "quick" tests, except that some files
  that test malloc and IO errors are omitted.
} -files [
  test_set $allquicktests -exclude *malloc* *ioerr* *fault* 
]

test_suite "quick" -prefix "" -description {
  Quick test suite. Runs in around 10 minutes on a workstation.
} -files [
  test_set $allquicktests
]







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lappend ::testsuitelist xxx

test_suite "veryquick" -prefix "" -description {
  "Very" quick test suite. Runs in less than 5 minutes on a workstation. 
  This test suite is the same as the "quick" tests, except that some files
  that test malloc and IO errors are omitted.
} -files [
  test_set $allquicktests -exclude *malloc* *ioerr* *fault*
]

test_suite "quick" -prefix "" -description {
  Quick test suite. Runs in around 10 minutes on a workstation.
} -files [
  test_set $allquicktests
]

Changes to test/threadtest3.c.

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      sqlite3_close(pDb->db);
      pDb->db = 0;
    }else{
      sqlite3_create_function(
          pDb->db, "md5sum", -1, SQLITE_UTF8, 0, 0, md5step, md5finalize
      );
      sqlite3_busy_handler(pDb->db, busyhandler, 0);

    }
  }
}

static void closedb_x(
  Error *pErr,                    /* IN/OUT: Error code */
  Sqlite *pDb                     /* OUT: Database handle */
................................................................................
  if( err.rc==SQLITE_OK ){
    printf("  WAL file is %d bytes,", (int)filesize(&err,"test.db-wal"));
    printf(" DB file is %d.\n", (int)filesize(&err,"test.db"));
  }

  print_and_free_err(&err);
}





















































int main(int argc, char **argv){
  struct ThreadTest {
    void (*xTest)(int);
    const char *zTest;
    int nMs;
  } aTest[] = {
    { walthread1, "walthread1", 20000 },
    { walthread2, "walthread2", 20000 },
    { walthread3, "walthread3", 20000 },
    { walthread4, "walthread4", 20000 },
    { walthread5, "walthread5",  1000 },



  };

  int i;
  char *zTest = 0;
  int nTest = 0;
  int bTestfound = 0;
  int bPrefix = 0;







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      sqlite3_close(pDb->db);
      pDb->db = 0;
    }else{
      sqlite3_create_function(
          pDb->db, "md5sum", -1, SQLITE_UTF8, 0, 0, md5step, md5finalize
      );
      sqlite3_busy_handler(pDb->db, busyhandler, 0);
      sqlite3_exec(pDb->db, "PRAGMA synchronous=OFF", 0, 0, 0);
    }
  }
}

static void closedb_x(
  Error *pErr,                    /* IN/OUT: Error code */
  Sqlite *pDb                     /* OUT: Database handle */
................................................................................
  if( err.rc==SQLITE_OK ){
    printf("  WAL file is %d bytes,", (int)filesize(&err,"test.db-wal"));
    printf(" DB file is %d.\n", (int)filesize(&err,"test.db"));
  }

  print_and_free_err(&err);
}

/*------------------------------------------------------------------------
** Test case "cgt_pager_1"
*/
#define CALLGRINDTEST1_NROW 10000
static void cgt_pager_1_populate(Error *pErr, Sqlite *pDb){
  const char *zInsert = "INSERT INTO t1 VALUES(:iRow, zeroblob(:iBlob))";
  i64 iRow;
  sql_script(pErr, pDb, "BEGIN");
  for(iRow=1; iRow<=CALLGRINDTEST1_NROW; iRow++){
    i64 iBlob = 600 + (iRow%300);
    execsql(pErr, pDb, zInsert, &iRow, &iBlob);
  }
  sql_script(pErr, pDb, "COMMIT");
}
static void cgt_pager_1_update(Error *pErr, Sqlite *pDb){
  const char *zUpdate = "UPDATE t1 SET b = zeroblob(:iBlob) WHERE a = :iRow";
  i64 iRow;
  sql_script(pErr, pDb, "BEGIN");
  for(iRow=1; iRow<=CALLGRINDTEST1_NROW; iRow++){
    i64 iBlob = 600 + ((iRow+100)%300);
    execsql(pErr, pDb, zUpdate, &iBlob, &iRow);
  }
  sql_script(pErr, pDb, "COMMIT");
}
static void cgt_pager_1_read(Error *pErr, Sqlite *pDb){
  i64 iRow;
  sql_script(pErr, pDb, "BEGIN");
  for(iRow=1; iRow<=CALLGRINDTEST1_NROW; iRow++){
    execsql(pErr, pDb, "SELECT * FROM t1 WHERE a = :iRow", &iRow);
  }
  sql_script(pErr, pDb, "COMMIT");
}
static void cgt_pager_1(int nMs){
  void (*xSub)(Error *, Sqlite *);
  Error err = {0};
  Sqlite db = {0};

  opendb(&err, &db, "test.db", 1);
  sql_script(&err, &db,
      "PRAGMA cache_size = 2000;"
      "PRAGMA page_size = 1024;"
      "CREATE TABLE t1(a INTEGER PRIMARY KEY, b BLOB);"
  );

  xSub = cgt_pager_1_populate; xSub(&err, &db);
  xSub = cgt_pager_1_update;   xSub(&err, &db);
  xSub = cgt_pager_1_read;     xSub(&err, &db);

  closedb(&err, &db);
  print_and_free_err(&err);
}

int main(int argc, char **argv){
  struct ThreadTest {
    void (*xTest)(int);
    const char *zTest;
    int nMs;
  } aTest[] = {
    { walthread1, "walthread1", 20000 },
    { walthread2, "walthread2", 20000 },
    { walthread3, "walthread3", 20000 },
    { walthread4, "walthread4", 20000 },
    { walthread5, "walthread5",  1000 },
    { walthread5, "walthread5",  1000 },
    
    { cgt_pager_1, "cgt_pager_1", 0 },
  };

  int i;
  char *zTest = 0;
  int nTest = 0;
  int bTestfound = 0;
  int bPrefix = 0;

Changes to test/wal2.test.

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  }
} {normal main exclusive temp closed}
do_test wal2-6.1.5 {
  execsql { 
    SELECT * FROM t1;
    PRAGMA lock_status;
  }
} {1 2 main exclusive temp closed}
do_test wal2-6.1.6 {
  execsql {
    INSERT INTO t1 VALUES(3, 4);
    PRAGMA lock_status;
  }
} {main shared temp closed}
db close
................................................................................
    BEGIN IMMEDIATE; COMMIT;
    PRAGMA locking_mode = NORMAL;
  }
  execsql {
    SELECT * FROM t1;
    pragma lock_status;
  }
} {1 2 3 4 main exclusive temp closed}
do_test wal2-6.2.9 {
  execsql {
    INSERT INTO t1 VALUES(5, 6);
    SELECT * FROM t1;
    pragma lock_status;
  }
} {1 2 3 4 5 6 main shared temp closed}
................................................................................
}
set READMARK1_SET {
  {4 1 lock exclusive} {4 1 unlock exclusive}
}
set READMARK1_READ {
  {4 1 lock shared} {4 1 unlock shared}
}






foreach {tn sql res expected_locks} {
  2 {
    PRAGMA journal_mode = WAL;
    BEGIN;
      CREATE TABLE t1(x);
      INSERT INTO t1 VALUES('Leonard');
................................................................................

  8 {
    PRAGMA locking_mode = normal
  } {normal} { }

  9 {
    SELECT * FROM t1 ORDER BY x
  } {Arthur {Julius Henry} Karl Leonard} { }

  10 {
    DELETE FROM t1
  } {} {
    $READMARK1_READ
  }

  11 {
    SELECT * FROM t1
  } {} {
    $READMARK1_SET
    $READMARK1_READ
  }
................................................................................
  faultsim_restore_and_reopen
  execsql { SELECT * FROM t1 }
} {1 2 3 4}
do_test wal2-10.2.2 { 
  set hdr [set_tvfs_hdr $::filename] 
  lindex $hdr 0 
} {3007000}
breakpoint
do_test wal2-10.2.3 { 
  lset hdr 0 3007001
  wal_fix_walindex_cksum hdr 
  set_tvfs_hdr $::filename $hdr
  catchsql { SELECT * FROM t1 }
} {1 {unable to open database file}}
db close
................................................................................
  set blob [string range [tvfs shm $::filename] 0 16383]
  append blob [string repeat [binary format c 55] 16384]
  tvfs shm $::filename $blob
  do_test wal2-11.3 {
    catchsql { SELECT * FROM t1 } db2
  } {1 {database disk image is malformed}}
}
  
db close
db2 close
tvfs delete

#-------------------------------------------------------------------------
# If a connection is required to create a WAL or SHM file, it creates 
# the new files with the same file-system permissions as the database 







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  }
} {normal main exclusive temp closed}
do_test wal2-6.1.5 {
  execsql { 
    SELECT * FROM t1;
    PRAGMA lock_status;
  }
} {1 2 main shared temp closed}
do_test wal2-6.1.6 {
  execsql {
    INSERT INTO t1 VALUES(3, 4);
    PRAGMA lock_status;
  }
} {main shared temp closed}
db close
................................................................................
    BEGIN IMMEDIATE; COMMIT;
    PRAGMA locking_mode = NORMAL;
  }
  execsql {
    SELECT * FROM t1;
    pragma lock_status;
  }
} {1 2 3 4 main shared temp closed}
do_test wal2-6.2.9 {
  execsql {
    INSERT INTO t1 VALUES(5, 6);
    SELECT * FROM t1;
    pragma lock_status;
  }
} {1 2 3 4 5 6 main shared temp closed}
................................................................................
}
set READMARK1_SET {
  {4 1 lock exclusive} {4 1 unlock exclusive}
}
set READMARK1_READ {
  {4 1 lock shared} {4 1 unlock shared}
}
set READMARK1_WRITE {
  {4 1 lock shared} 
    {0 1 lock exclusive} {0 1 unlock exclusive} 
  {4 1 unlock shared}
}

foreach {tn sql res expected_locks} {
  2 {
    PRAGMA journal_mode = WAL;
    BEGIN;
      CREATE TABLE t1(x);
      INSERT INTO t1 VALUES('Leonard');
................................................................................

  8 {
    PRAGMA locking_mode = normal
  } {normal} { }

  9 {
    SELECT * FROM t1 ORDER BY x
  } {Arthur {Julius Henry} Karl Leonard} $READMARK1_READ


  10 { DELETE FROM t1 } {} $READMARK1_WRITE




  11 {
    SELECT * FROM t1
  } {} {
    $READMARK1_SET
    $READMARK1_READ
  }
................................................................................
  faultsim_restore_and_reopen
  execsql { SELECT * FROM t1 }
} {1 2 3 4}
do_test wal2-10.2.2 { 
  set hdr [set_tvfs_hdr $::filename] 
  lindex $hdr 0 
} {3007000}

do_test wal2-10.2.3 { 
  lset hdr 0 3007001
  wal_fix_walindex_cksum hdr 
  set_tvfs_hdr $::filename $hdr
  catchsql { SELECT * FROM t1 }
} {1 {unable to open database file}}
db close
................................................................................
  set blob [string range [tvfs shm $::filename] 0 16383]
  append blob [string repeat [binary format c 55] 16384]
  tvfs shm $::filename $blob
  do_test wal2-11.3 {
    catchsql { SELECT * FROM t1 } db2
  } {1 {database disk image is malformed}}
}

db close
db2 close
tvfs delete

#-------------------------------------------------------------------------
# If a connection is required to create a WAL or SHM file, it creates 
# the new files with the same file-system permissions as the database 

Changes to test/wal3.test.

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    execsql { SELECT x FROM t1 WHERE rowid = $i }
  } $str
  do_test wal3-1.$i.7 {
    execsql { PRAGMA integrity_check } db2
  } {ok}
  db2 close
}






do_multiclient_test i {

  set testname(1) multiproc
  set testname(2) singleproc
  set tn $testname($i)

................................................................................
  # no-op, as the entire log has already been backfilled.
  #
  do_test wal3-2.$tn.4 {
    sql1 {
      COMMIT;
      PRAGMA wal_checkpoint;
    }
    file size test.db
  } [expr $AUTOVACUUM ? 4*1024 : 3*1024]
  do_test wal3-2.$tn.5 {
    sql2 {
      COMMIT;
      PRAGMA wal_checkpoint;
    }
    file size test.db
  } [expr $AUTOVACUUM ? 5*1024 : 4*1024]

  do_test wal3-2.$tn.6 {
    sql3 {
      COMMIT;
      PRAGMA wal_checkpoint;
    }
    file size test.db
  } [expr $AUTOVACUUM ? 5*1024 : 4*1024]

}
catch {db close}

#-------------------------------------------------------------------------
# Test that that for the simple test:
#
#   CREATE TABLE x(y);
................................................................................
# the client takes a shared-lock on a slot without modifying the value
# and continues.
#
do_test wal3-9.0 {
  file delete -force test.db test.db-journal test.db wal
  sqlite3 db test.db
  execsql {

    PRAGMA journal_mode = WAL;
    CREATE TABLE whoami(x);
    INSERT INTO whoami VALUES('nobody');
  }
} {wal}
for {set i 0} {$i < 50} {incr i} {
  set c db$i
................................................................................
}
for {set i 0} {$i < 50} {incr i} {
  set c db$i
  do_test wal3-9.2.$i {
    execsql { SELECT * FROM whoami } $c
  } $c
}


do_test wal3-9.3 {
  for {set i 0} {$i < 49} {incr i} { db$i close }
  execsql { PRAGMA wal_checkpoint } 
  set sz1 [file size test.db]


  db49 close
  execsql { PRAGMA wal_checkpoint } 
  set sz2 [file size test.db]
  expr {$sz2 > $sz1}
} {1}

db close

finish_test








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105
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    execsql { SELECT x FROM t1 WHERE rowid = $i }
  } $str
  do_test wal3-1.$i.7 {
    execsql { PRAGMA integrity_check } db2
  } {ok}
  db2 close
}

proc byte_is_zero {file offset} {
  if {[file size test.db] <= $offset} { return 1 }
  expr { [hexio_read $file $offset 1] == "00" }
}

do_multiclient_test i {

  set testname(1) multiproc
  set testname(2) singleproc
  set tn $testname($i)

................................................................................
  # no-op, as the entire log has already been backfilled.
  #
  do_test wal3-2.$tn.4 {
    sql1 {
      COMMIT;
      PRAGMA wal_checkpoint;
    }
    byte_is_zero test.db [expr $AUTOVACUUM ? 4*1024 : 3*1024]
  } {1}
  do_test wal3-2.$tn.5 {
    sql2 {
      COMMIT;
      PRAGMA wal_checkpoint;
    }
    list [byte_is_zero test.db [expr $AUTOVACUUM ? 4*1024 : 3*1024]]   \
         [byte_is_zero test.db [expr $AUTOVACUUM ? 5*1024 : 4*1024]]
  } {0 1}
  do_test wal3-2.$tn.6 {
    sql3 {
      COMMIT;
      PRAGMA wal_checkpoint;
    }
    list [byte_is_zero test.db [expr $AUTOVACUUM ? 4*1024 : 3*1024]]   \
         [byte_is_zero test.db [expr $AUTOVACUUM ? 5*1024 : 4*1024]]
  } {0 1}
}
catch {db close}

#-------------------------------------------------------------------------
# Test that that for the simple test:
#
#   CREATE TABLE x(y);
................................................................................
# the client takes a shared-lock on a slot without modifying the value
# and continues.
#
do_test wal3-9.0 {
  file delete -force test.db test.db-journal test.db wal
  sqlite3 db test.db
  execsql {
    PRAGMA page_size = 1024;
    PRAGMA journal_mode = WAL;
    CREATE TABLE whoami(x);
    INSERT INTO whoami VALUES('nobody');
  }
} {wal}
for {set i 0} {$i < 50} {incr i} {
  set c db$i
................................................................................
}
for {set i 0} {$i < 50} {incr i} {
  set c db$i
  do_test wal3-9.2.$i {
    execsql { SELECT * FROM whoami } $c
  } $c
}

set sz [expr 1024 * (2+$AUTOVACUUM)]
do_test wal3-9.3 {
  for {set i 0} {$i < 49} {incr i} { db$i close }
  execsql { PRAGMA wal_checkpoint } 
  byte_is_zero test.db [expr $sz-1024]
} {1}
do_test wal3-9.4 {
  db49 close
  execsql { PRAGMA wal_checkpoint } 
  set sz2 [file size test.db]
  byte_is_zero test.db [expr $sz-1024]
} {0}

db close

finish_test

Changes to test/walmode.test.

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380
do_execsql_test walmode-8.16 { PRAGMA two.journal_mode   }         {wal}
do_execsql_test walmode-8.17 { INSERT INTO two.t2 DEFAULT VALUES } {}
do_execsql_test walmode-8.18 { PRAGMA two.journal_mode   }         {wal}
 
sqlite3 db2 test.db2
do_test walmode-8.19 { execsql { PRAGMA main.journal_mode } db2 }  {wal}
db2 close








finish_test








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do_execsql_test walmode-8.16 { PRAGMA two.journal_mode   }         {wal}
do_execsql_test walmode-8.17 { INSERT INTO two.t2 DEFAULT VALUES } {}
do_execsql_test walmode-8.18 { PRAGMA two.journal_mode   }         {wal}
 
sqlite3 db2 test.db2
do_test walmode-8.19 { execsql { PRAGMA main.journal_mode } db2 }  {wal}
db2 close

do_execsql_test walmode-8.20 { PRAGMA journal_mode = DELETE } {delete}
do_execsql_test walmode-8.21 { PRAGMA main.journal_mode }     {delete}
do_execsql_test walmode-8.22 { PRAGMA two.journal_mode }      {delete}
do_execsql_test walmode-8.21 { PRAGMA journal_mode = WAL }    {wal}
do_execsql_test walmode-8.21 { PRAGMA main.journal_mode }     {wal}
do_execsql_test walmode-8.22 { PRAGMA two.journal_mode }      {wal}

finish_test