** page size of pgsz bytes. The offset returned is to the start of the
** log frame-header.
*/
#define logFrameOffset(iFrame, pgsz) (                               \
  LOG_HDRSIZE + ((iFrame)-1)*((pgsz)+LOG_FRAME_HDRSIZE)              \
)










/*
** There is one instance of this structure for each log-summary object
** that this process has a connection to. They are stored in a linked
** list starting at pLogSummary (global variable).
**
** TODO: LogSummary.fd is a unix file descriptor. Unix APIs are used 
**       directly in this implementation because the VFS does not support
................................................................................
struct LogSummary {
  sqlite3_mutex *mutex;           /* Mutex used to protect this object */
  int nRef;                       /* Number of pointers to this structure */
  int fd;                         /* File descriptor open on log-summary */
  char *zPath;                    /* Path to associated WAL file */
  LogLock *pLock;                 /* Linked list of locks on this object */
  LogSummary *pNext;              /* Next in global list */

  int nData;                      /* Size of aData allocation/mapping */
  u32 *aData;                     /* File body */
};

/*
** This module uses three different types of file-locks. All are taken
** on the log-summary file. The three types of locks are as follows:
................................................................................
  u64 sum2 = aCksum[1];
  u32 *a32 = (u32 *)aByte;
  u32 *aEnd = (u32 *)&aByte[nByte];

  assert( LOG_CKSM_BYTES==2*sizeof(u32) );
  assert( (nByte&0x00000003)==0 );






  do {
    sum1 += (*a32++);
    sum2 += sum1;
  } while( a32<aEnd );








  aCksum[0] = sum1 + (sum1>>24);
  aCksum[1] = sum2 + (sum2>>24);
}

/*
** Argument zPath must be a nul-terminated string containing a path-name.
................................................................................
      }
    }
    z[j++] = z[i];
  }
  z[j] = 0;
}

/*
** Memory map the first nByte bytes of the summary file opened with 
** pSummary->fd at pSummary->aData. If the summary file is smaller than
** nByte bytes in size when this function is called, ftruncate() is
** used to expand it before it is mapped.
**
** It is assumed that an exclusive lock is held on the summary file
** by the caller (to protect the ftruncate()).
*/
static int logSummaryMap(LogSummary *pSummary, int nByte){
  struct stat sStat;
  int rc;
  int fd = pSummary->fd;
  void *pMap;

  assert( pSummary->aData==0 );

  /* If the file is less than nByte bytes in size, cause it to grow. */
  rc = fstat(fd, &sStat);
  if( rc!=0 ) return SQLITE_IOERR;
  if( sStat.st_size<nByte ){
    rc = ftruncate(fd, nByte);
    if( rc!=0 ) return SQLITE_IOERR;
  }

  /* Map the file. */
  pMap = mmap(0, nByte, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
  if( pMap==MAP_FAILED ){
    return SQLITE_IOERR;
  }
  pSummary->aData = (u32 *)pMap;
  pSummary->nData = nByte;

  return SQLITE_OK;
}

/*
** Unmap the log-summary mapping and close the file-descriptor. If
** the isTruncate argument is non-zero, truncate the log-summary file
** region to zero bytes.
**
** Regardless of the value of isTruncate, close the file-descriptor
** opened on the log-summary file.
................................................................................
    for(i=1; i<*pnList; i++){
      assert( aContent[aList[i]] > aContent[aList[i-1]] );
    }
  }
#endif
}








































/*
** Return the index in the LogSummary.aData array that corresponds to 
** frame iFrame. The log-summary file consists of a header, followed by
** alternating "map" and "index" blocks.
*/
static int logSummaryEntry(u32 iFrame){
................................................................................
** page iPage. Values are always appended to the log-summary (i.e. the
** value of iFrame is always exactly one more than the value passed to
** the previous call), but that restriction is not enforced or asserted
** here.
*/
static void logSummaryAppend(LogSummary *pSummary, u32 iFrame, u32 iPage){
  u32 iSlot = logSummaryEntry(iFrame);











  /* Set the log-summary entry itself */
  pSummary->aData[iSlot] = iPage;

  /* If the frame number is a multiple of 256 (frames are numbered starting
  ** at 1), build an index of the most recently added 256 frames.
  */
................................................................................
      return rc;
    }

    /* If the database page size is not a power of two, or is greater than
    ** SQLITE_MAX_PAGE_SIZE, conclude that the log file contains no valid data.
    */
    nPgsz = sqlite3Get4byte(&aBuf[0]);
    if( nPgsz&(nPgsz-1) || nPgsz>SQLITE_MAX_PAGE_SIZE ){
      goto finished;
    }
    aCksum[0] = sqlite3Get4byte(&aBuf[4]);
    aCksum[1] = sqlite3Get4byte(&aBuf[8]);

    /* Malloc a buffer to read frames into. */
    nFrame = nPgsz + LOG_FRAME_HDRSIZE;
................................................................................
  ** pages should not be allocated until they are first accessed anyhow,
  ** so using a large mapping consumes no more resources than a smaller
  ** one would.
  */
  assert( sqlite3_mutex_held(pSummary->mutex) );
  rc = logLockMutex(pSummary, LOG_WRLOCKW);
  if( rc!=SQLITE_OK ) return rc;
  rc = logSummaryMap(pSummary, 512*1024);
  if( rc!=SQLITE_OK ) goto out;

  /* Try to obtain an EXCLUSIVE lock on the dead-mans-hand region. If this
  ** is possible, the contents of the log-summary file (if any) may not
  ** be trusted. Zero the log-summary header before continuing.
  */
  rc = logLockDMH(pSummary, LOG_WRLOCK);

** page size of pgsz bytes. The offset returned is to the start of the
** log frame-header.
*/
#define logFrameOffset(iFrame, pgsz) (                               \
  LOG_HDRSIZE + ((iFrame)-1)*((pgsz)+LOG_FRAME_HDRSIZE)              \
)

/*
** If using mmap() to access a shared (or otherwise) log-summary file, then
** the mapping size is incremented in units of the following size.
**
** A 64 KB log-summary mapping corresponds to a log file containing over
** 13000 frames, so the mapping size does not need to be increased often.
*/
#define LOGSUMMARY_MMAP_INCREMENT (64*1024)

/*
** There is one instance of this structure for each log-summary object
** that this process has a connection to. They are stored in a linked
** list starting at pLogSummary (global variable).
**
** TODO: LogSummary.fd is a unix file descriptor. Unix APIs are used 
**       directly in this implementation because the VFS does not support
................................................................................
struct LogSummary {
  sqlite3_mutex *mutex;           /* Mutex used to protect this object */
  int nRef;                       /* Number of pointers to this structure */
  int fd;                         /* File descriptor open on log-summary */
  char *zPath;                    /* Path to associated WAL file */
  LogLock *pLock;                 /* Linked list of locks on this object */
  LogSummary *pNext;              /* Next in global list */

  int nData;                      /* Size of aData allocation/mapping */
  u32 *aData;                     /* File body */
};

/*
** This module uses three different types of file-locks. All are taken
** on the log-summary file. The three types of locks are as follows:
................................................................................
  u64 sum2 = aCksum[1];
  u32 *a32 = (u32 *)aByte;
  u32 *aEnd = (u32 *)&aByte[nByte];

  assert( LOG_CKSM_BYTES==2*sizeof(u32) );
  assert( (nByte&0x00000003)==0 );

  if( SQLITE_LITTLEENDIAN ){
#ifdef SQLITE_DEBUG
    u8 *a = (u8 *)a32;
    assert( *a32==(a[0] + (a[1]<<8) + (a[2]<<16) + (a[3]<<24)) );
#endif
    do {
      sum1 += *a32;
      sum2 += sum1;
    } while( ++a32<aEnd );
  }else{
    do {
      u8 *a = (u8*)a32;
      sum1 += a[0] + (a[1]<<8) + (a[2]<<16) + (a[3]<<24);
      sum2 += sum1;
    } while( ++a32<aEnd );
  }

  aCksum[0] = sum1 + (sum1>>24);
  aCksum[1] = sum2 + (sum2>>24);
}

/*
** Argument zPath must be a nul-terminated string containing a path-name.
................................................................................
      }
    }
    z[j++] = z[i];
  }
  z[j] = 0;
}





































/*
** Unmap the log-summary mapping and close the file-descriptor. If
** the isTruncate argument is non-zero, truncate the log-summary file
** region to zero bytes.
**
** Regardless of the value of isTruncate, close the file-descriptor
** opened on the log-summary file.
................................................................................
    for(i=1; i<*pnList; i++){
      assert( aContent[aList[i]] > aContent[aList[i-1]] );
    }
  }
#endif
}


/*
** Memory map the first nByte bytes of the summary file opened with 
** pSummary->fd at pSummary->aData. If the summary file is smaller than
** nByte bytes in size when this function is called, ftruncate() is
** used to expand it before it is mapped.
**
** It is assumed that an exclusive lock is held on the summary file
** by the caller (to protect the ftruncate()).
*/
static int logSummaryMap(LogSummary *pSummary, int nByte){
  struct stat sStat;
  int rc;
  int fd = pSummary->fd;
  void *pMap;

  assert( pSummary->aData==0 );

  /* If the file is less than nByte bytes in size, cause it to grow. */
  rc = fstat(fd, &sStat);
  if( rc!=0 ) return SQLITE_IOERR;
  if( sStat.st_size<nByte ){
    rc = ftruncate(fd, nByte);
    if( rc!=0 ) return SQLITE_IOERR;
  }else{
    nByte = sStat.st_size;
  }

  /* Map the file. */
  pMap = mmap(0, nByte, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
  if( pMap==MAP_FAILED ){
    return SQLITE_IOERR;
  }
  pSummary->aData = (u32 *)pMap;
  pSummary->nData = nByte/4;

  return SQLITE_OK;
}

/*
** Return the index in the LogSummary.aData array that corresponds to 
** frame iFrame. The log-summary file consists of a header, followed by
** alternating "map" and "index" blocks.
*/
static int logSummaryEntry(u32 iFrame){
................................................................................
** page iPage. Values are always appended to the log-summary (i.e. the
** value of iFrame is always exactly one more than the value passed to
** the previous call), but that restriction is not enforced or asserted
** here.
*/
static void logSummaryAppend(LogSummary *pSummary, u32 iFrame, u32 iPage){
  u32 iSlot = logSummaryEntry(iFrame);

  if( (iSlot+128)>=pSummary->nData ){
    int nByte = pSummary->nData*4 + LOGSUMMARY_MMAP_INCREMENT;

    sqlite3_mutex_enter(pSummary->mutex);
    munmap(pSummary->aData, pSummary->nData*4);
    pSummary->aData = 0;
    logSummaryMap(pSummary, nByte);
    sqlite3_mutex_leave(pSummary->mutex);
  }

  /* Set the log-summary entry itself */
  pSummary->aData[iSlot] = iPage;

  /* If the frame number is a multiple of 256 (frames are numbered starting
  ** at 1), build an index of the most recently added 256 frames.
  */
................................................................................
      return rc;
    }

    /* If the database page size is not a power of two, or is greater than
    ** SQLITE_MAX_PAGE_SIZE, conclude that the log file contains no valid data.
    */
    nPgsz = sqlite3Get4byte(&aBuf[0]);
    if( nPgsz&(nPgsz-1) || nPgsz>SQLITE_MAX_PAGE_SIZE || nPgsz<512 ){
      goto finished;
    }
    aCksum[0] = sqlite3Get4byte(&aBuf[4]);
    aCksum[1] = sqlite3Get4byte(&aBuf[8]);

    /* Malloc a buffer to read frames into. */
    nFrame = nPgsz + LOG_FRAME_HDRSIZE;
................................................................................
  ** pages should not be allocated until they are first accessed anyhow,
  ** so using a large mapping consumes no more resources than a smaller
  ** one would.
  */
  assert( sqlite3_mutex_held(pSummary->mutex) );
  rc = logLockMutex(pSummary, LOG_WRLOCKW);
  if( rc!=SQLITE_OK ) return rc;
  rc = logSummaryMap(pSummary, LOGSUMMARY_MMAP_INCREMENT);
  if( rc!=SQLITE_OK ) goto out;

  /* Try to obtain an EXCLUSIVE lock on the dead-mans-hand region. If this
  ** is possible, the contents of the log-summary file (if any) may not
  ** be trusted. Zero the log-summary header before continuing.
  */
  rc = logLockDMH(pSummary, LOG_WRLOCK);

    rc = SQLITE_OK;
    *pExists = 0;
  }
  return rc;
}

static int pagerOpenSnapshot(Pager *pPager){
  int rc;
  int changed;

  assert( pagerUseLog(pPager) );

  rc = sqlite3LogOpenSnapshot(pPager->pLog, &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;
}

    rc = SQLITE_OK;
    *pExists = 0;
  }
  return rc;
}

static int pagerOpenSnapshot(Pager *pPager){
  int rc;                         /* Return code */
  int changed = 0;                /* True if cache must be reset */

  assert( pagerUseLog(pPager) );

  rc = sqlite3LogOpenSnapshot(pPager->pLog, &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;
}

  }
  list [expr [file size test.db]/1024] [expr [file size test.db-wal]/1044]
} {3 1}
do_test wal-12.3 {
  execsql { INSERT INTO t2 VALUES('B', 1) }
  list [expr [file size test.db]/1024] [expr [file size test.db-wal]/1044]
} {3 2}

do_test wal-12.4 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 1}
db2 close

do_test wal-12.5 {
  execsql {
    PRAGMA checkpoint;
    UPDATE t2 SET y = 2 WHERE x = 'B'; 
    PRAGMA checkpoint;
    UPDATE t1 SET y = 1 WHERE x = 'A';
    PRAGMA checkpoint;
    UPDATE t1 SET y = 0 WHERE x = 'A';
    SELECT * FROM t2;
  }
} {B 2}

do_test wal-12.4 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 2}
db2 close



































finish_test

  }
  list [expr [file size test.db]/1024] [expr [file size test.db-wal]/1044]
} {3 1}
do_test wal-12.3 {
  execsql { INSERT INTO t2 VALUES('B', 1) }
  list [expr [file size test.db]/1024] [expr [file size test.db-wal]/1044]
} {3 2}

do_test wal-12.4 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 1}
db2 close

do_test wal-12.5 {
  execsql {
    PRAGMA checkpoint;
    UPDATE t2 SET y = 2 WHERE x = 'B'; 
    PRAGMA checkpoint;
    UPDATE t1 SET y = 1 WHERE x = 'A';
    PRAGMA checkpoint;
    UPDATE t1 SET y = 0 WHERE x = 'A';
    SELECT * FROM t2;
  }
} {B 2}

do_test wal-12.6 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 2}
db2 close
db close

#-------------------------------------------------------------------------
# Test large log summaries.
#
do_test wal-13.1 {
  list [file exists test.db] [file exists test.db-wal]
} {1 0}
do_test wal-13.2 {
  set fd [open test.db-wal w]
  seek $fd [expr 200*1024*1024]
  puts $fd ""
  close $fd
  sqlite3 db test.db
  execsql { SELECT * FROM t2 }
} {B 2}
do_test wal-13.3 {
  db close
  file exists test.db-wal
} {0}
do_test wal-13.4 {
  sqlite3 db test.db
  execsql { SELECT count(*) FROM t2 }
} {1}
do_test wal-13.5 {
  for {set i 0} {$i < 15} {incr i} {
    execsql { INSERT INTO t2 SELECT randomblob(400), randomblob(400) FROM t2 }
  }
  execsql { SELECT count(*) FROM t2 }
} [expr int(pow(2, 15))]
do_test wal-13.6 {
  file size test.db-wal-summary
} [expr 192*1024]


finish_test