SQLite

        zKey = (char *)sqlite3_value_blob(argv[2]);
        rc = sqlite3CodecAttach(db, db->nDb-1, zKey, nKey);
        break;

      case SQLITE_NULL:
        /* No key specified.  Use the key from the main database */
        sqlite3CodecGetKey(db, 0, (void**)&zKey, &nKey);
        if( nKey>0 || sqlite3BtreeGetOptimalReserve(db->aDb[0].pBt)>0 ){
          rc = sqlite3CodecAttach(db, db->nDb-1, zKey, nKey);
        }
        break;
    }
  }
#endif

  const int nCopy = MIN(nSrcPgsz, nDestPgsz);
  const i64 iEnd = (i64)iSrcPg*(i64)nSrcPgsz;
#ifdef SQLITE_HAS_CODEC
  /* Use BtreeGetReserveNoMutex() for the source b-tree, as although it is
  ** guaranteed that the shared-mutex is held by this thread, handle
  ** p->pSrc may not actually be the owner.  */
  int nSrcReserve = sqlite3BtreeGetReserveNoMutex(p->pSrc);
  int nDestReserve = sqlite3BtreeGetOptimalReserve(p->pDest);
#endif
  int rc = SQLITE_OK;
  i64 iOff;

  assert( sqlite3BtreeGetReserveNoMutex(p->pSrc)>=0 );
  assert( p->bDestLocked );
  assert( !isFatalError(p->rc) );

** and autovacuum mode can no longer be changed.
*/
int sqlite3BtreeSetPageSize(Btree *p, int pageSize, int nReserve, int iFix){
  int rc = SQLITE_OK;
  BtShared *pBt = p->pBt;
  assert( nReserve>=-1 && nReserve<=255 );
  sqlite3BtreeEnter(p);
#if SQLITE_HAS_CODEC
  if( nReserve>pBt->optimalReserve ) pBt->optimalReserve = (u8)nReserve;
#endif
  if( pBt->btsFlags & BTS_PAGESIZE_FIXED ){
    sqlite3BtreeLeave(p);
    return SQLITE_READONLY;
  }
  if( nReserve<0 ){
    nReserve = pBt->pageSize - pBt->usableSize;
  }

/*
** Return the currently defined page size
*/
int sqlite3BtreeGetPageSize(Btree *p){
  return p->pBt->pageSize;
}


/*
** This function is similar to sqlite3BtreeGetReserve(), except that it
** may only be called if it is guaranteed that the b-tree mutex is already
** held.
**
** This is useful in one special case in the backup API code where it is
** known that the shared b-tree mutex is held, but the mutex on the 
** database handle that owns *p is not. In this case if sqlite3BtreeEnter()
** were to be called, it might collide with some other operation on the
** database handle that owns *p, causing undefined behavior.
*/
int sqlite3BtreeGetReserveNoMutex(Btree *p){
  int n;
  assert( sqlite3_mutex_held(p->pBt->mutex) );
  n = p->pBt->pageSize - p->pBt->usableSize;
  return n;
}



/*
** Return the number of bytes of space at the end of every page that
** are intentually left unused.  This is the "reserved" space that is
** sometimes used by extensions.
**
** If SQLITE_HAS_MUTEX is defined then the number returned is the
** greater of the current reserved space and the maximum requested
** reserve space.
*/
int sqlite3BtreeGetOptimalReserve(Btree *p){
  int n;
  sqlite3BtreeEnter(p);
  n = sqlite3BtreeGetReserveNoMutex(p);
#ifdef SQLITE_HAS_CODEC
  if( n<p->pBt->optimalReserve ) n = p->pBt->optimalReserve;
#endif
  sqlite3BtreeLeave(p);
  return n;
}


/*
** Set the maximum page count for a database if mxPage is positive.
** No changes are made if mxPage is 0 or negative.
** Regardless of the value of mxPage, return the maximum page count.
*/
int sqlite3BtreeMaxPageCount(Btree *p, int mxPage){

    p->pBt->btsFlags &= ~BTS_SECURE_DELETE;
    if( newFlag ) p->pBt->btsFlags |= BTS_SECURE_DELETE;
  } 
  b = (p->pBt->btsFlags & BTS_SECURE_DELETE)!=0;
  sqlite3BtreeLeave(p);
  return b;
}


/*
** Change the 'auto-vacuum' property of the database. If the 'autoVacuum'
** parameter is non-zero, then auto-vacuum mode is enabled. If zero, it
** is disabled. The default value for the auto-vacuum property is 
** determined by the SQLITE_DEFAULT_AUTOVACUUM macro.
*/

int sqlite3BtreeSetPagerFlags(Btree*,unsigned);
int sqlite3BtreeSyncDisabled(Btree*);
int sqlite3BtreeSetPageSize(Btree *p, int nPagesize, int nReserve, int eFix);
int sqlite3BtreeGetPageSize(Btree*);
int sqlite3BtreeMaxPageCount(Btree*,int);
u32 sqlite3BtreeLastPage(Btree*);
int sqlite3BtreeSecureDelete(Btree*,int);
int sqlite3BtreeGetOptimalReserve(Btree*);

int sqlite3BtreeGetReserveNoMutex(Btree *p);

int sqlite3BtreeSetAutoVacuum(Btree *, int);
int sqlite3BtreeGetAutoVacuum(Btree *);
int sqlite3BtreeBeginTrans(Btree*,int);
int sqlite3BtreeCommitPhaseOne(Btree*, const char *zMaster);
int sqlite3BtreeCommitPhaseTwo(Btree*, int);
int sqlite3BtreeCommit(Btree*);
int sqlite3BtreeRollback(Btree*,int,int);

#ifndef SQLITE_OMIT_AUTOVACUUM
  u8 autoVacuum;        /* True if auto-vacuum is enabled */
  u8 incrVacuum;        /* True if incr-vacuum is enabled */
  u8 bDoTruncate;       /* True to truncate db on commit */
#endif
  u8 inTransaction;     /* Transaction state */
  u8 max1bytePayload;   /* Maximum first byte of cell for a 1-byte payload */
#ifdef SQLITE_HAS_CODEC
  u8 optimalReserve;    /* Desired amount of reserved space per page */
#endif
  u16 btsFlags;         /* Boolean parameters.  See BTS_* macros below */
  u16 maxLocal;         /* Maximum local payload in non-LEAFDATA tables */
  u16 minLocal;         /* Minimum local payload in non-LEAFDATA tables */
  u16 maxLeaf;          /* Maximum local payload in a LEAFDATA table */
  u16 minLeaf;          /* Minimum local payload in a LEAFDATA table */
  u32 pageSize;         /* Total number of bytes on a page */
  u32 usableSize;       /* Number of usable bytes on each page */

#ifdef SQLITE_EBCDIC
      0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, /* 0x */
     16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, /* 1x */
     32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, /* 2x */
     48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, /* 3x */
     64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, /* 4x */
     80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, /* 5x */
     96, 97, 98, 99,100,101,102,103,104,105,106,107,108,109,110,111, /* 6x */
    112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127, /* 7x */
    128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143, /* 8x */
    144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159, /* 9x */
    160,161,162,163,164,165,166,167,168,169,170,171,140,141,142,175, /* Ax */
    176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191, /* Bx */
    192,129,130,131,132,133,134,135,136,137,202,203,204,205,206,207, /* Cx */
    208,145,146,147,148,149,150,151,152,153,218,219,220,221,222,223, /* Dx */
    224,225,162,163,164,165,166,167,168,169,234,235,236,237,238,239, /* Ex */
    240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255, /* Fx */
#endif
};

/*
** The following 256 byte lookup table is used to support SQLites built-in
** equivalents to the following standard library functions:
**

#else
# define UNIXFILE_DIRSYNC    0x00
#endif
#define UNIXFILE_PSOW        0x10     /* SQLITE_IOCAP_POWERSAFE_OVERWRITE */
#define UNIXFILE_DELETE      0x20     /* Delete on close */
#define UNIXFILE_URI         0x40     /* Filename might have query parameters */
#define UNIXFILE_NOLOCK      0x80     /* Do no file locking */
#define UNIXFILE_WARNED    0x0100     /* verifyDbFile() warnings issued */

/*
** Include code that is common to all os_*.c files
*/
#include "os_common.h"

/*

#undef osFcntl
#define osFcntl lockTrace
#endif /* SQLITE_LOCK_TRACE */

/*
** Retry ftruncate() calls that fail due to EINTR
**
** All calls to ftruncate() within this file should be made through
** this wrapper.  On the Android platform, bypassing the logic below
** could lead to a corrupt database.
*/
static int robust_ftruncate(int h, sqlite3_int64 sz){
  int rc;
#ifdef __ANDROID__
  /* On Android, ftruncate() always uses 32-bit offsets, even if 
  ** _FILE_OFFSET_BITS=64 is defined. This means it is unsafe to attempt to
  ** truncate a file to any size larger than 2GiB. Silently ignore any

  if( osClose(h) ){
    unixLogErrorAtLine(SQLITE_IOERR_CLOSE, "close",
                       pFile ? pFile->zPath : 0, lineno);
  }
}

/*
** Set the pFile->lastErrno.  Do this in a subroutine as that provides
** a convenient place to set a breakpoint.
*/
static void storeLastErrno(unixFile *pFile, int error){
  pFile->lastErrno = error;
}

/*
** Close all file descriptors accumuated in the unixInodeInfo->pUnused list.

    ** write lock until the rest is covered by a read lock:
    **  1:   [WWWWW]
    **  2:   [....W]
    **  3:   [RRRRW]
    **  4:   [RRRR.]
    */
    if( eFileLock==SHARED_LOCK ){


#if !defined(__APPLE__) || !SQLITE_ENABLE_LOCKING_STYLE
      (void)handleNFSUnlock;
      assert( handleNFSUnlock==0 );
#endif
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
      if( handleNFSUnlock ){
        int tErrno;               /* Error code from system call errors */
        off_t divSize = SHARED_SIZE - 1;
        
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock, 10)==(-1) ){

#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
      {
        lock.l_type = F_RDLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = SHARED_SIZE;
        if( unixFileLock(pFile, &lock, 10) ){
          int tErrno = errno;
#if OSLOCKING_CHECK_BUSY_IOERR
          rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_RDLOCK);
#else
          /* In theory, the call to unixFileLock() cannot fail because another
          ** process is holding an incompatible lock. If it does, this 
          ** indicates that the other process is not following the locking
          ** protocol. If this happens, return SQLITE_IOERR_RDLOCK. Returning

  assert( nBuf==(nBuf&0x1ffff) );
  assert( fd>2 );
  nBuf &= 0x1ffff;
  TIMER_START;

#if defined(USE_PREAD)
  do{ rc = (int)osPwrite(fd, pBuf, nBuf, iOff); }while( rc<0 && errno==EINTR );
#elif defined(USE_PREAD64)
  do{ rc = (int)osPwrite64(fd, pBuf, nBuf, iOff);}while( rc<0 && errno==EINTR);
#else
  do{
    i64 iSeek = lseek(fd, iOff, SEEK_SET);
    SimulateIOError( iSeek-- );

    if( iSeek!=iOff ){
      if( piErrno ) *piErrno = (iSeek==-1 ? errno : 0);

**
**   *  A constant sqlite3_io_methods object call METHOD that has locking
**      methods CLOSE, LOCK, UNLOCK, CKRESLOCK.
**
**   *  An I/O method finder function called FINDER that returns a pointer
**      to the METHOD object in the previous bullet.
*/
#define IOMETHODS(FINDER,METHOD,VERSION,CLOSE,LOCK,UNLOCK,CKLOCK,SHMMAP)     \
static const sqlite3_io_methods METHOD = {                                   \
   VERSION,                    /* iVersion */                                \
   CLOSE,                      /* xClose */                                  \
   unixRead,                   /* xRead */                                   \
   unixWrite,                  /* xWrite */                                  \
   unixTruncate,               /* xTruncate */                               \
   unixSync,                   /* xSync */                                   \

        continue; 
      }
      
      assert( pCtx->nFails>=3 );
      if( (pCtx->nFails==3)&&(0==proxyBreakConchLock(pFile, myHostID)) ){
        rc = SQLITE_OK;
        if( lockType==EXCLUSIVE_LOCK ){
          rc = conchFile->pMethod->xLock((sqlite3_file*)conchFile, SHARED_LOCK);
        }
        if( !rc ){
          rc = conchFile->pMethod->xLock((sqlite3_file*)conchFile, lockType);
        }
      }
    }
  } while( rc==SQLITE_BUSY && pCtx->nFails<3 );

  }
  p->nUnused = nUnused;
  p->iRightChildPg = isLeaf ? 0 : sqlite3Get4byte(&aHdr[8]);
  szPage = sqlite3BtreeGetPageSize(pBt);

  if( p->nCell ){
    int i;                        /* Used to iterate through cells */
    int nUsable;                  /* Usable bytes per page */

    sqlite3BtreeEnter(pBt);
    nUsable = szPage - sqlite3BtreeGetReserveNoMutex(pBt);
    sqlite3BtreeLeave(pBt);
    p->aCell = sqlite3_malloc((p->nCell+1) * sizeof(StatCell));
    memset(p->aCell, 0, (p->nCell+1) * sizeof(StatCell));

    for(i=0; i<p->nCell; i++){
      StatCell *pCell = &p->aCell[i];

      iOff = get2byte(&aData[nHdr+i*2]);

    /* Page p itself has already been visited. */
    StatPage *p = &pCsr->aPage[pCsr->iPage];

    while( p->iCell<p->nCell ){
      StatCell *pCell = &p->aCell[p->iCell];
      if( pCell->iOvfl<pCell->nOvfl ){
        int nUsable;
        sqlite3BtreeEnter(pBt);
        nUsable = sqlite3BtreeGetPageSize(pBt) - 
                        sqlite3BtreeGetReserveNoMutex(pBt);
        sqlite3BtreeLeave(pBt);
        pCsr->zName = (char *)sqlite3_column_text(pCsr->pStmt, 0);
        pCsr->iPageno = pCell->aOvfl[pCell->iOvfl];
        pCsr->zPagetype = "overflow";
        pCsr->nCell = 0;
        pCsr->nMxPayload = 0;
        pCsr->zPath = sqlite3_mprintf(
            "%s%.3x+%.6x", p->zPath, p->iCell, pCell->iOvfl

  /* The call to execSql() to attach the temp database has left the file
  ** locked (as there was more than one active statement when the transaction
  ** to read the schema was concluded. Unlock it here so that this doesn't
  ** cause problems for the call to BtreeSetPageSize() below.  */
  sqlite3BtreeCommit(pTemp);

  nRes = sqlite3BtreeGetOptimalReserve(pMain);

  /* A VACUUM cannot change the pagesize of an encrypted database. */
#ifdef SQLITE_HAS_CODEC
  if( db->nextPagesize ){
    extern void sqlite3CodecGetKey(sqlite3*, int, void**, int*);
    int nKey;
    char *zKey;