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 */

  }
  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;