1 files changed, 6890 insertions, 0 deletions

diff --git a/libraries/sqlite/win32/btree.c b/libraries/sqlite/win32/btree.c
new file mode 100755
index 0000000..de8821a
--- /dev/null
+++ b/libraries/sqlite/win32/btree.c
@@ -0,0 +1,6890 @@
+/*
+** 2004 April 6
+**
+** 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.
+**
+*************************************************************************
+** $Id: btree.c,v 1.428 2007/10/03 08:46:44 danielk1977 Exp $
+**
+** This file implements a external (disk-based) database using BTrees.
+** See the header comment on "btreeInt.h" for additional information.
+** Including a description of file format and an overview of operation.
+*/
+#include "btreeInt.h"
+
+/*
+** The header string that appears at the beginning of every
+** SQLite database.
+*/
+static const char zMagicHeader[] = SQLITE_FILE_HEADER;
+
+/*
+** Set this global variable to 1 to enable tracing using the TRACE
+** macro.
+*/
+#if SQLITE_TEST
+int sqlite3_btree_trace=0;  /* True to enable tracing */
+#endif
+
+
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+/*
+** A flag to indicate whether or not shared cache is enabled.  Also,
+** a list of BtShared objects that are eligible for participation
+** in shared cache.  The variables have file scope during normal builds,
+** but the test harness needs to access these variables so we make them
+** global for test builds.
+*/
+#ifdef SQLITE_TEST
+BtShared *sqlite3SharedCacheList = 0;
+int sqlite3SharedCacheEnabled = 0;
+#else
+static BtShared *sqlite3SharedCacheList = 0;
+static int sqlite3SharedCacheEnabled = 0;
+#endif
+#endif /* SQLITE_OMIT_SHARED_CACHE */
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+/*
+** Enable or disable the shared pager and schema features.
+**
+** This routine has no effect on existing database connections.
+** The shared cache setting effects only future calls to
+** sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2().
+*/
+int sqlite3_enable_shared_cache(int enable){
+  sqlite3SharedCacheEnabled = enable;
+  return SQLITE_OK;
+}
+#endif
+
+
+/*
+** Forward declaration
+*/
+static int checkReadLocks(Btree*,Pgno,BtCursor*);
+
+
+#ifdef SQLITE_OMIT_SHARED_CACHE
+  /*
+  ** The functions queryTableLock(), lockTable() and unlockAllTables()
+  ** manipulate entries in the BtShared.pLock linked list used to store
+  ** shared-cache table level locks. If the library is compiled with the
+  ** shared-cache feature disabled, then there is only ever one user
+  ** of each BtShared structure and so this locking is not necessary. 
+  ** So define the lock related functions as no-ops.
+  */
+  #define queryTableLock(a,b,c) SQLITE_OK
+  #define lockTable(a,b,c) SQLITE_OK
+  #define unlockAllTables(a)
+#endif
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+/*
+** Query to see if btree handle p may obtain a lock of type eLock 
+** (READ_LOCK or WRITE_LOCK) on the table with root-page iTab. Return
+** SQLITE_OK if the lock may be obtained (by calling lockTable()), or
+** SQLITE_LOCKED if not.
+*/
+static int queryTableLock(Btree *p, Pgno iTab, u8 eLock){
+  BtShared *pBt = p->pBt;
+  BtLock *pIter;
+
+  assert( sqlite3BtreeHoldsMutex(p) );
+  
+  /* This is a no-op if the shared-cache is not enabled */
+  if( !p->sharable ){
+    return SQLITE_OK;
+  }
+
+  /* This (along with lockTable()) is where the ReadUncommitted flag is
+  ** dealt with. If the caller is querying for a read-lock and the flag is
+  ** set, it is unconditionally granted - even if there are write-locks
+  ** on the table. If a write-lock is requested, the ReadUncommitted flag
+  ** is not considered.
+  **
+  ** In function lockTable(), if a read-lock is demanded and the 
+  ** ReadUncommitted flag is set, no entry is added to the locks list 
+  ** (BtShared.pLock).
+  **
+  ** To summarize: If the ReadUncommitted flag is set, then read cursors do
+  ** not create or respect table locks. The locking procedure for a 
+  ** write-cursor does not change.
+  */
+  if( 
+    !p->pSqlite || 
+    0==(p->pSqlite->flags&SQLITE_ReadUncommitted) || 
+    eLock==WRITE_LOCK ||
+    iTab==MASTER_ROOT
+  ){
+    for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
+      if( pIter->pBtree!=p && pIter->iTable==iTab && 
+          (pIter->eLock!=eLock || eLock!=READ_LOCK) ){
+        return SQLITE_LOCKED;
+      }
+    }
+  }
+  return SQLITE_OK;
+}
+#endif /* !SQLITE_OMIT_SHARED_CACHE */
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+/*
+** Add a lock on the table with root-page iTable to the shared-btree used
+** by Btree handle p. Parameter eLock must be either READ_LOCK or 
+** WRITE_LOCK.
+**
+** SQLITE_OK is returned if the lock is added successfully. SQLITE_BUSY and
+** SQLITE_NOMEM may also be returned.
+*/
+static int lockTable(Btree *p, Pgno iTable, u8 eLock){
+  BtShared *pBt = p->pBt;
+  BtLock *pLock = 0;
+  BtLock *pIter;
+
+  assert( sqlite3BtreeHoldsMutex(p) );
+
+  /* This is a no-op if the shared-cache is not enabled */
+  if( !p->sharable ){
+    return SQLITE_OK;
+  }
+
+  assert( SQLITE_OK==queryTableLock(p, iTable, eLock) );
+
+  /* If the read-uncommitted flag is set and a read-lock is requested,
+  ** return early without adding an entry to the BtShared.pLock list. See
+  ** comment in function queryTableLock() for more info on handling 
+  ** the ReadUncommitted flag.
+  */
+  if( 
+    (p->pSqlite) && 
+    (p->pSqlite->flags&SQLITE_ReadUncommitted) && 
+    (eLock==READ_LOCK) &&
+    iTable!=MASTER_ROOT
+  ){
+    return SQLITE_OK;
+  }
+
+  /* First search the list for an existing lock on this table. */
+  for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
+    if( pIter->iTable==iTable && pIter->pBtree==p ){
+      pLock = pIter;
+      break;
+    }
+  }
+
+  /* If the above search did not find a BtLock struct associating Btree p
+  ** with table iTable, allocate one and link it into the list.
+  */
+  if( !pLock ){
+    pLock = (BtLock *)sqlite3MallocZero(sizeof(BtLock));
+    if( !pLock ){
+      return SQLITE_NOMEM;
+    }
+    pLock->iTable = iTable;
+    pLock->pBtree = p;
+    pLock->pNext = pBt->pLock;
+    pBt->pLock = pLock;
+  }
+
+  /* Set the BtLock.eLock variable to the maximum of the current lock
+  ** and the requested lock. This means if a write-lock was already held
+  ** and a read-lock requested, we don't incorrectly downgrade the lock.
+  */
+  assert( WRITE_LOCK>READ_LOCK );
+  if( eLock>pLock->eLock ){
+    pLock->eLock = eLock;
+  }
+
+  return SQLITE_OK;
+}
+#endif /* !SQLITE_OMIT_SHARED_CACHE */
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+/*
+** Release all the table locks (locks obtained via calls to the lockTable()
+** procedure) held by Btree handle p.
+*/
+static void unlockAllTables(Btree *p){
+  BtLock **ppIter = &p->pBt->pLock;
+
+  assert( sqlite3BtreeHoldsMutex(p) );
+  assert( p->sharable || 0==*ppIter );
+
+  while( *ppIter ){
+    BtLock *pLock = *ppIter;
+    if( pLock->pBtree==p ){
+      *ppIter = pLock->pNext;
+      sqlite3_free(pLock);
+    }else{
+      ppIter = &pLock->pNext;
+    }
+  }
+}
+#endif /* SQLITE_OMIT_SHARED_CACHE */
+
+static void releasePage(MemPage *pPage);  /* Forward reference */
+
+/*
+** Verify that the cursor holds a mutex on the BtShared
+*/
+#ifndef NDEBUG
+static int cursorHoldsMutex(BtCursor *p){
+  return sqlite3_mutex_held(p->pBt->mutex);
+}
+#endif
+
+
+#ifndef SQLITE_OMIT_INCRBLOB
+/*
+** Invalidate the overflow page-list cache for cursor pCur, if any.
+*/
+static void invalidateOverflowCache(BtCursor *pCur){
+  assert( cursorHoldsMutex(pCur) );
+  sqlite3_free(pCur->aOverflow);
+  pCur->aOverflow = 0;
+}
+
+/*
+** Invalidate the overflow page-list cache for all cursors opened
+** on the shared btree structure pBt.
+*/
+static void invalidateAllOverflowCache(BtShared *pBt){
+  BtCursor *p;
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  for(p=pBt->pCursor; p; p=p->pNext){
+    invalidateOverflowCache(p);
+  }
+}
+#else
+  #define invalidateOverflowCache(x)
+  #define invalidateAllOverflowCache(x)
+#endif
+
+/*
+** Save the current cursor position in the variables BtCursor.nKey 
+** and BtCursor.pKey. The cursor's state is set to CURSOR_REQUIRESEEK.
+*/
+static int saveCursorPosition(BtCursor *pCur){
+  int rc;
+
+  assert( CURSOR_VALID==pCur->eState );
+  assert( 0==pCur->pKey );
+  assert( cursorHoldsMutex(pCur) );
+
+  rc = sqlite3BtreeKeySize(pCur, &pCur->nKey);
+
+  /* If this is an intKey table, then the above call to BtreeKeySize()
+  ** stores the integer key in pCur->nKey. In this case this value is
+  ** all that is required. Otherwise, if pCur is not open on an intKey
+  ** table, then malloc space for and store the pCur->nKey bytes of key 
+  ** data.
+  */
+  if( rc==SQLITE_OK && 0==pCur->pPage->intKey){
+    void *pKey = sqlite3_malloc(pCur->nKey);
+    if( pKey ){
+      rc = sqlite3BtreeKey(pCur, 0, pCur->nKey, pKey);
+      if( rc==SQLITE_OK ){
+        pCur->pKey = pKey;
+      }else{
+        sqlite3_free(pKey);
+      }
+    }else{
+      rc = SQLITE_NOMEM;
+    }
+  }
+  assert( !pCur->pPage->intKey || !pCur->pKey );
+
+  if( rc==SQLITE_OK ){
+    releasePage(pCur->pPage);
+    pCur->pPage = 0;
+    pCur->eState = CURSOR_REQUIRESEEK;
+  }
+
+  invalidateOverflowCache(pCur);
+  return rc;
+}
+
+/*
+** Save the positions of all cursors except pExcept open on the table 
+** with root-page iRoot. Usually, this is called just before cursor
+** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
+*/
+static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
+  BtCursor *p;
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  assert( pExcept==0 || pExcept->pBt==pBt );
+  for(p=pBt->pCursor; p; p=p->pNext){
+    if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) && 
+        p->eState==CURSOR_VALID ){
+      int rc = saveCursorPosition(p);
+      if( SQLITE_OK!=rc ){
+        return rc;
+      }
+    }
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Clear the current cursor position.
+*/
+static void clearCursorPosition(BtCursor *pCur){
+  assert( cursorHoldsMutex(pCur) );
+  sqlite3_free(pCur->pKey);
+  pCur->pKey = 0;
+  pCur->eState = CURSOR_INVALID;
+}
+
+/*
+** Restore the cursor to the position it was in (or as close to as possible)
+** when saveCursorPosition() was called. Note that this call deletes the 
+** saved position info stored by saveCursorPosition(), so there can be
+** at most one effective restoreOrClearCursorPosition() call after each 
+** saveCursorPosition().
+**
+** If the second argument argument - doSeek - is false, then instead of 
+** returning the cursor to it's saved position, any saved position is deleted
+** and the cursor state set to CURSOR_INVALID.
+*/
+int sqlite3BtreeRestoreOrClearCursorPosition(BtCursor *pCur){
+  int rc;
+  assert( cursorHoldsMutex(pCur) );
+  assert( pCur->eState>=CURSOR_REQUIRESEEK );
+  if( pCur->eState==CURSOR_FAULT ){
+    return pCur->skip;
+  }
+#ifndef SQLITE_OMIT_INCRBLOB
+  if( pCur->isIncrblobHandle ){
+    return SQLITE_ABORT;
+  }
+#endif
+  pCur->eState = CURSOR_INVALID;
+  rc = sqlite3BtreeMoveto(pCur, pCur->pKey, pCur->nKey, 0, &pCur->skip);
+  if( rc==SQLITE_OK ){
+    sqlite3_free(pCur->pKey);
+    pCur->pKey = 0;
+    assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_INVALID );
+  }
+  return rc;
+}
+
+#define restoreOrClearCursorPosition(p) \
+  (p->eState>=CURSOR_REQUIRESEEK ? \
+         sqlite3BtreeRestoreOrClearCursorPosition(p) : \
+         SQLITE_OK)
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+/*
+** Given a page number of a regular database page, return the page
+** number for the pointer-map page that contains the entry for the
+** input page number.
+*/
+static Pgno ptrmapPageno(BtShared *pBt, Pgno pgno){
+  int nPagesPerMapPage, iPtrMap, ret;
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  nPagesPerMapPage = (pBt->usableSize/5)+1;
+  iPtrMap = (pgno-2)/nPagesPerMapPage;
+  ret = (iPtrMap*nPagesPerMapPage) + 2; 
+  if( ret==PENDING_BYTE_PAGE(pBt) ){
+    ret++;
+  }
+  return ret;
+}
+
+/*
+** Write an entry into the pointer map.
+**
+** This routine updates the pointer map entry for page number 'key'
+** so that it maps to type 'eType' and parent page number 'pgno'.
+** An error code is returned if something goes wrong, otherwise SQLITE_OK.
+*/
+static int ptrmapPut(BtShared *pBt, Pgno key, u8 eType, Pgno parent){
+  DbPage *pDbPage;  /* The pointer map page */
+  u8 *pPtrmap;      /* The pointer map data */
+  Pgno iPtrmap;     /* The pointer map page number */
+  int offset;       /* Offset in pointer map page */
+  int rc;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  /* The master-journal page number must never be used as a pointer map page */
+  assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );
+
+  assert( pBt->autoVacuum );
+  if( key==0 ){
+    return SQLITE_CORRUPT_BKPT;
+  }
+  iPtrmap = PTRMAP_PAGENO(pBt, key);
+  rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  offset = PTRMAP_PTROFFSET(pBt, key);
+  pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);
+
+  if( eType!=pPtrmap[offset] || get4byte(&pPtrmap[offset+1])!=parent ){
+    TRACE(("PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent));
+    rc = sqlite3PagerWrite(pDbPage);
+    if( rc==SQLITE_OK ){
+      pPtrmap[offset] = eType;
+      put4byte(&pPtrmap[offset+1], parent);
+    }
+  }
+
+  sqlite3PagerUnref(pDbPage);
+  return rc;
+}
+
+/*
+** Read an entry from the pointer map.
+**
+** This routine retrieves the pointer map entry for page 'key', writing
+** the type and parent page number to *pEType and *pPgno respectively.
+** An error code is returned if something goes wrong, otherwise SQLITE_OK.
+*/
+static int ptrmapGet(BtShared *pBt, Pgno key, u8 *pEType, Pgno *pPgno){
+  DbPage *pDbPage;   /* The pointer map page */
+  int iPtrmap;       /* Pointer map page index */
+  u8 *pPtrmap;       /* Pointer map page data */
+  int offset;        /* Offset of entry in pointer map */
+  int rc;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+
+  iPtrmap = PTRMAP_PAGENO(pBt, key);
+  rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
+  if( rc!=0 ){
+    return rc;
+  }
+  pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);
+
+  offset = PTRMAP_PTROFFSET(pBt, key);
+  assert( pEType!=0 );
+  *pEType = pPtrmap[offset];
+  if( pPgno ) *pPgno = get4byte(&pPtrmap[offset+1]);
+
+  sqlite3PagerUnref(pDbPage);
+  if( *pEType<1 || *pEType>5 ) return SQLITE_CORRUPT_BKPT;
+  return SQLITE_OK;
+}
+
+#endif /* SQLITE_OMIT_AUTOVACUUM */
+
+/*
+** Given a btree page and a cell index (0 means the first cell on
+** the page, 1 means the second cell, and so forth) return a pointer
+** to the cell content.
+**
+** This routine works only for pages that do not contain overflow cells.
+*/
+#define findCell(pPage, iCell) \
+  ((pPage)->aData + get2byte(&(pPage)->aData[(pPage)->cellOffset+2*(iCell)]))
+#ifdef SQLITE_TEST
+u8 *sqlite3BtreeFindCell(MemPage *pPage, int iCell){
+  assert( iCell>=0 );
+  assert( iCell<get2byte(&pPage->aData[pPage->hdrOffset+3]) );
+  return findCell(pPage, iCell);
+}
+#endif
+
+/*
+** This a more complex version of sqlite3BtreeFindCell() that works for
+** pages that do contain overflow cells.  See insert
+*/
+static u8 *findOverflowCell(MemPage *pPage, int iCell){
+  int i;
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  for(i=pPage->nOverflow-1; i>=0; i--){
+    int k;
+    struct _OvflCell *pOvfl;
+    pOvfl = &pPage->aOvfl[i];
+    k = pOvfl->idx;
+    if( k<=iCell ){
+      if( k==iCell ){
+        return pOvfl->pCell;
+      }
+      iCell--;
+    }
+  }
+  return findCell(pPage, iCell);
+}
+
+/*
+** Parse a cell content block and fill in the CellInfo structure.  There
+** are two versions of this function.  sqlite3BtreeParseCell() takes a 
+** cell index as the second argument and sqlite3BtreeParseCellPtr() 
+** takes a pointer to the body of the cell as its second argument.
+**
+** Within this file, the parseCell() macro can be called instead of
+** sqlite3BtreeParseCellPtr(). Using some compilers, this will be faster.
+*/
+void sqlite3BtreeParseCellPtr(
+  MemPage *pPage,         /* Page containing the cell */
+  u8 *pCell,              /* Pointer to the cell text. */
+  CellInfo *pInfo         /* Fill in this structure */
+){
+  int n;                  /* Number bytes in cell content header */
+  u32 nPayload;           /* Number of bytes of cell payload */
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+
+  pInfo->pCell = pCell;
+  assert( pPage->leaf==0 || pPage->leaf==1 );
+  n = pPage->childPtrSize;
+  assert( n==4-4*pPage->leaf );
+  if( pPage->hasData ){
+    n += getVarint32(&pCell[n], &nPayload);
+  }else{
+    nPayload = 0;
+  }
+  pInfo->nData = nPayload;
+  if( pPage->intKey ){
+    n += getVarint(&pCell[n], (u64 *)&pInfo->nKey);
+  }else{
+    u32 x;
+    n += getVarint32(&pCell[n], &x);
+    pInfo->nKey = x;
+    nPayload += x;
+  }
+  pInfo->nPayload = nPayload;
+  pInfo->nHeader = n;
+  if( nPayload<=pPage->maxLocal ){
+    /* This is the (easy) common case where the entire payload fits
+    ** on the local page.  No overflow is required.
+    */
+    int nSize;          /* Total size of cell content in bytes */
+    pInfo->nLocal = nPayload;
+    pInfo->iOverflow = 0;
+    nSize = nPayload + n;
+    if( nSize<4 ){
+      nSize = 4;        /* Minimum cell size is 4 */
+    }
+    pInfo->nSize = nSize;
+  }else{
+    /* If the payload will not fit completely on the local page, we have
+    ** to decide how much to store locally and how much to spill onto
+    ** overflow pages.  The strategy is to minimize the amount of unused
+    ** space on overflow pages while keeping the amount of local storage
+    ** in between minLocal and maxLocal.
+    **
+    ** Warning:  changing the way overflow payload is distributed in any
+    ** way will result in an incompatible file format.
+    */
+    int minLocal;  /* Minimum amount of payload held locally */
+    int maxLocal;  /* Maximum amount of payload held locally */
+    int surplus;   /* Overflow payload available for local storage */
+
+    minLocal = pPage->minLocal;
+    maxLocal = pPage->maxLocal;
+    surplus = minLocal + (nPayload - minLocal)%(pPage->pBt->usableSize - 4);
+    if( surplus <= maxLocal ){
+      pInfo->nLocal = surplus;
+    }else{
+      pInfo->nLocal = minLocal;
+    }
+    pInfo->iOverflow = pInfo->nLocal + n;
+    pInfo->nSize = pInfo->iOverflow + 4;
+  }
+}
+#define parseCell(pPage, iCell, pInfo) \
+  sqlite3BtreeParseCellPtr((pPage), findCell((pPage), (iCell)), (pInfo))
+void sqlite3BtreeParseCell(
+  MemPage *pPage,         /* Page containing the cell */
+  int iCell,              /* The cell index.  First cell is 0 */
+  CellInfo *pInfo         /* Fill in this structure */
+){
+  parseCell(pPage, iCell, pInfo);
+}
+
+/*
+** Compute the total number of bytes that a Cell needs in the cell
+** data area of the btree-page.  The return number includes the cell
+** data header and the local payload, but not any overflow page or
+** the space used by the cell pointer.
+*/
+#ifndef NDEBUG
+static int cellSize(MemPage *pPage, int iCell){
+  CellInfo info;
+  sqlite3BtreeParseCell(pPage, iCell, &info);
+  return info.nSize;
+}
+#endif
+static int cellSizePtr(MemPage *pPage, u8 *pCell){
+  CellInfo info;
+  sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+  return info.nSize;
+}
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+/*
+** If the cell pCell, part of page pPage contains a pointer
+** to an overflow page, insert an entry into the pointer-map
+** for the overflow page.
+*/
+static int ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell){
+  if( pCell ){
+    CellInfo info;
+    sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+    assert( (info.nData+(pPage->intKey?0:info.nKey))==info.nPayload );
+    if( (info.nData+(pPage->intKey?0:info.nKey))>info.nLocal ){
+      Pgno ovfl = get4byte(&pCell[info.iOverflow]);
+      return ptrmapPut(pPage->pBt, ovfl, PTRMAP_OVERFLOW1, pPage->pgno);
+    }
+  }
+  return SQLITE_OK;
+}
+/*
+** If the cell with index iCell on page pPage contains a pointer
+** to an overflow page, insert an entry into the pointer-map
+** for the overflow page.
+*/
+static int ptrmapPutOvfl(MemPage *pPage, int iCell){
+  u8 *pCell;
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  pCell = findOverflowCell(pPage, iCell);
+  return ptrmapPutOvflPtr(pPage, pCell);
+}
+#endif
+
+
+/*
+** Defragment the page given.  All Cells are moved to the
+** end of the page and all free space is collected into one
+** big FreeBlk that occurs in between the header and cell
+** pointer array and the cell content area.
+*/
+static int defragmentPage(MemPage *pPage){
+  int i;                     /* Loop counter */
+  int pc;                    /* Address of a i-th cell */
+  int addr;                  /* Offset of first byte after cell pointer array */
+  int hdr;                   /* Offset to the page header */
+  int size;                  /* Size of a cell */
+  int usableSize;            /* Number of usable bytes on a page */
+  int cellOffset;            /* Offset to the cell pointer array */
+  int brk;                   /* Offset to the cell content area */
+  int nCell;                 /* Number of cells on the page */
+  unsigned char *data;       /* The page data */
+  unsigned char *temp;       /* Temp area for cell content */
+
+  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
+  assert( pPage->pBt!=0 );
+  assert( pPage->pBt->usableSize <= SQLITE_MAX_PAGE_SIZE );
+  assert( pPage->nOverflow==0 );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  temp = sqlite3_malloc( pPage->pBt->pageSize );
+  if( temp==0 ) return SQLITE_NOMEM;
+  data = pPage->aData;
+  hdr = pPage->hdrOffset;
+  cellOffset = pPage->cellOffset;
+  nCell = pPage->nCell;
+  assert( nCell==get2byte(&data[hdr+3]) );
+  usableSize = pPage->pBt->usableSize;
+  brk = get2byte(&data[hdr+5]);
+  memcpy(&temp[brk], &data[brk], usableSize - brk);
+  brk = usableSize;
+  for(i=0; i<nCell; i++){
+    u8 *pAddr;     /* The i-th cell pointer */
+    pAddr = &data[cellOffset + i*2];
+    pc = get2byte(pAddr);
+    assert( pc<pPage->pBt->usableSize );
+    size = cellSizePtr(pPage, &temp[pc]);
+    brk -= size;
+    memcpy(&data[brk], &temp[pc], size);
+    put2byte(pAddr, brk);
+  }
+  assert( brk>=cellOffset+2*nCell );
+  put2byte(&data[hdr+5], brk);
+  data[hdr+1] = 0;
+  data[hdr+2] = 0;
+  data[hdr+7] = 0;
+  addr = cellOffset+2*nCell;
+  memset(&data[addr], 0, brk-addr);
+  sqlite3_free(temp);
+  return SQLITE_OK;
+}
+
+/*
+** Allocate nByte bytes of space on a page.
+**
+** Return the index into pPage->aData[] of the first byte of
+** the new allocation. Or return 0 if there is not enough free
+** space on the page to satisfy the allocation request.
+**
+** If the page contains nBytes of free space but does not contain
+** nBytes of contiguous free space, then this routine automatically
+** calls defragementPage() to consolidate all free space before 
+** allocating the new chunk.
+*/
+static int allocateSpace(MemPage *pPage, int nByte){
+  int addr, pc, hdr;
+  int size;
+  int nFrag;
+  int top;
+  int nCell;
+  int cellOffset;
+  unsigned char *data;
+  
+  data = pPage->aData;
+  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
+  assert( pPage->pBt );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( nByte<4 ) nByte = 4;
+  if( pPage->nFree<nByte || pPage->nOverflow>0 ) return 0;
+  pPage->nFree -= nByte;
+  hdr = pPage->hdrOffset;
+
+  nFrag = data[hdr+7];
+  if( nFrag<60 ){
+    /* Search the freelist looking for a slot big enough to satisfy the
+    ** space request. */
+    addr = hdr+1;
+    while( (pc = get2byte(&data[addr]))>0 ){
+      size = get2byte(&data[pc+2]);
+      if( size>=nByte ){
+        if( size<nByte+4 ){
+          memcpy(&data[addr], &data[pc], 2);
+          data[hdr+7] = nFrag + size - nByte;
+          return pc;
+        }else{
+          put2byte(&data[pc+2], size-nByte);
+          return pc + size - nByte;
+        }
+      }
+      addr = pc;
+    }
+  }
+
+  /* Allocate memory from the gap in between the cell pointer array
+  ** and the cell content area.
+  */
+  top = get2byte(&data[hdr+5]);
+  nCell = get2byte(&data[hdr+3]);
+  cellOffset = pPage->cellOffset;
+  if( nFrag>=60 || cellOffset + 2*nCell > top - nByte ){
+    if( defragmentPage(pPage) ) return 0;
+    top = get2byte(&data[hdr+5]);
+  }
+  top -= nByte;
+  assert( cellOffset + 2*nCell <= top );
+  put2byte(&data[hdr+5], top);
+  return top;
+}
+
+/*
+** Return a section of the pPage->aData to the freelist.
+** The first byte of the new free block is pPage->aDisk[start]
+** and the size of the block is "size" bytes.
+**
+** Most of the effort here is involved in coalesing adjacent
+** free blocks into a single big free block.
+*/
+static void freeSpace(MemPage *pPage, int start, int size){
+  int addr, pbegin, hdr;
+  unsigned char *data = pPage->aData;
+
+  assert( pPage->pBt!=0 );
+  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
+  assert( start>=pPage->hdrOffset+6+(pPage->leaf?0:4) );
+  assert( (start + size)<=pPage->pBt->usableSize );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( size<4 ) size = 4;
+
+#ifdef SQLITE_SECURE_DELETE
+  /* Overwrite deleted information with zeros when the SECURE_DELETE 
+  ** option is enabled at compile-time */
+  memset(&data[start], 0, size);
+#endif
+
+  /* Add the space back into the linked list of freeblocks */
+  hdr = pPage->hdrOffset;
+  addr = hdr + 1;
+  while( (pbegin = get2byte(&data[addr]))<start && pbegin>0 ){
+    assert( pbegin<=pPage->pBt->usableSize-4 );
+    assert( pbegin>addr );
+    addr = pbegin;
+  }
+  assert( pbegin<=pPage->pBt->usableSize-4 );
+  assert( pbegin>addr || pbegin==0 );
+  put2byte(&data[addr], start);
+  put2byte(&data[start], pbegin);
+  put2byte(&data[start+2], size);
+  pPage->nFree += size;
+
+  /* Coalesce adjacent free blocks */
+  addr = pPage->hdrOffset + 1;
+  while( (pbegin = get2byte(&data[addr]))>0 ){
+    int pnext, psize;
+    assert( pbegin>addr );
+    assert( pbegin<=pPage->pBt->usableSize-4 );
+    pnext = get2byte(&data[pbegin]);
+    psize = get2byte(&data[pbegin+2]);
+    if( pbegin + psize + 3 >= pnext && pnext>0 ){
+      int frag = pnext - (pbegin+psize);
+      assert( frag<=data[pPage->hdrOffset+7] );
+      data[pPage->hdrOffset+7] -= frag;
+      put2byte(&data[pbegin], get2byte(&data[pnext]));
+      put2byte(&data[pbegin+2], pnext+get2byte(&data[pnext+2])-pbegin);
+    }else{
+      addr = pbegin;
+    }
+  }
+
+  /* If the cell content area begins with a freeblock, remove it. */
+  if( data[hdr+1]==data[hdr+5] && data[hdr+2]==data[hdr+6] ){
+    int top;
+    pbegin = get2byte(&data[hdr+1]);
+    memcpy(&data[hdr+1], &data[pbegin], 2);
+    top = get2byte(&data[hdr+5]);
+    put2byte(&data[hdr+5], top + get2byte(&data[pbegin+2]));
+  }
+}
+
+/*
+** Decode the flags byte (the first byte of the header) for a page
+** and initialize fields of the MemPage structure accordingly.
+*/
+static void decodeFlags(MemPage *pPage, int flagByte){
+  BtShared *pBt;     /* A copy of pPage->pBt */
+
+  assert( pPage->hdrOffset==(pPage->pgno==1 ? 100 : 0) );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  pPage->intKey = (flagByte & (PTF_INTKEY|PTF_LEAFDATA))!=0;
+  pPage->zeroData = (flagByte & PTF_ZERODATA)!=0;
+  pPage->leaf = (flagByte & PTF_LEAF)!=0;
+  pPage->childPtrSize = 4*(pPage->leaf==0);
+  pBt = pPage->pBt;
+  if( flagByte & PTF_LEAFDATA ){
+    pPage->leafData = 1;
+    pPage->maxLocal = pBt->maxLeaf;
+    pPage->minLocal = pBt->minLeaf;
+  }else{
+    pPage->leafData = 0;
+    pPage->maxLocal = pBt->maxLocal;
+    pPage->minLocal = pBt->minLocal;
+  }
+  pPage->hasData = !(pPage->zeroData || (!pPage->leaf && pPage->leafData));
+}
+
+/*
+** Initialize the auxiliary information for a disk block.
+**
+** The pParent parameter must be a pointer to the MemPage which
+** is the parent of the page being initialized.  The root of a
+** BTree has no parent and so for that page, pParent==NULL.
+**
+** Return SQLITE_OK on success.  If we see that the page does
+** not contain a well-formed database page, then return 
+** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
+** guarantee that the page is well-formed.  It only shows that
+** we failed to detect any corruption.
+*/
+int sqlite3BtreeInitPage(
+  MemPage *pPage,        /* The page to be initialized */
+  MemPage *pParent       /* The parent.  Might be NULL */
+){
+  int pc;            /* Address of a freeblock within pPage->aData[] */
+  int hdr;           /* Offset to beginning of page header */
+  u8 *data;          /* Equal to pPage->aData */
+  BtShared *pBt;        /* The main btree structure */
+  int usableSize;    /* Amount of usable space on each page */
+  int cellOffset;    /* Offset from start of page to first cell pointer */
+  int nFree;         /* Number of unused bytes on the page */
+  int top;           /* First byte of the cell content area */
+
+  pBt = pPage->pBt;
+  assert( pBt!=0 );
+  assert( pParent==0 || pParent->pBt==pBt );
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  assert( pPage->pgno==sqlite3PagerPagenumber(pPage->pDbPage) );
+  assert( pPage == sqlite3PagerGetExtra(pPage->pDbPage) );
+  assert( pPage->aData == sqlite3PagerGetData(pPage->pDbPage) );
+  if( pPage->pParent!=pParent && (pPage->pParent!=0 || pPage->isInit) ){
+    /* The parent page should never change unless the file is corrupt */
+    return SQLITE_CORRUPT_BKPT;
+  }
+  if( pPage->isInit ) return SQLITE_OK;
+  if( pPage->pParent==0 && pParent!=0 ){
+    pPage->pParent = pParent;
+    sqlite3PagerRef(pParent->pDbPage);
+  }
+  hdr = pPage->hdrOffset;
+  data = pPage->aData;
+  decodeFlags(pPage, data[hdr]);
+  pPage->nOverflow = 0;
+  pPage->idxShift = 0;
+  usableSize = pBt->usableSize;
+  pPage->cellOffset = cellOffset = hdr + 12 - 4*pPage->leaf;
+  top = get2byte(&data[hdr+5]);
+  pPage->nCell = get2byte(&data[hdr+3]);
+  if( pPage->nCell>MX_CELL(pBt) ){
+    /* To many cells for a single page.  The page must be corrupt */
+    return SQLITE_CORRUPT_BKPT;
+  }
+  if( pPage->nCell==0 && pParent!=0 && pParent->pgno!=1 ){
+    /* All pages must have at least one cell, except for root pages */
+    return SQLITE_CORRUPT_BKPT;
+  }
+
+  /* Compute the total free space on the page */
+  pc = get2byte(&data[hdr+1]);
+  nFree = data[hdr+7] + top - (cellOffset + 2*pPage->nCell);
+  while( pc>0 ){
+    int next, size;
+    if( pc>usableSize-4 ){
+      /* Free block is off the page */
+      return SQLITE_CORRUPT_BKPT; 
+    }
+    next = get2byte(&data[pc]);
+    size = get2byte(&data[pc+2]);
+    if( next>0 && next<=pc+size+3 ){
+      /* Free blocks must be in accending order */
+      return SQLITE_CORRUPT_BKPT; 
+    }
+    nFree += size;
+    pc = next;
+  }
+  pPage->nFree = nFree;
+  if( nFree>=usableSize ){
+    /* Free space cannot exceed total page size */
+    return SQLITE_CORRUPT_BKPT; 
+  }
+
+  pPage->isInit = 1;
+  return SQLITE_OK;
+}
+
+/*
+** Set up a raw page so that it looks like a database page holding
+** no entries.
+*/
+static void zeroPage(MemPage *pPage, int flags){
+  unsigned char *data = pPage->aData;
+  BtShared *pBt = pPage->pBt;
+  int hdr = pPage->hdrOffset;
+  int first;
+
+  assert( sqlite3PagerPagenumber(pPage->pDbPage)==pPage->pgno );
+  assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
+  assert( sqlite3PagerGetData(pPage->pDbPage) == data );
+  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  memset(&data[hdr], 0, pBt->usableSize - hdr);
+  data[hdr] = flags;
+  first = hdr + 8 + 4*((flags&PTF_LEAF)==0);
+  memset(&data[hdr+1], 0, 4);
+  data[hdr+7] = 0;
+  put2byte(&data[hdr+5], pBt->usableSize);
+  pPage->nFree = pBt->usableSize - first;
+  decodeFlags(pPage, flags);
+  pPage->hdrOffset = hdr;
+  pPage->cellOffset = first;
+  pPage->nOverflow = 0;
+  pPage->idxShift = 0;
+  pPage->nCell = 0;
+  pPage->isInit = 1;
+}
+
+/*
+** Get a page from the pager.  Initialize the MemPage.pBt and
+** MemPage.aData elements if needed.
+**
+** If the noContent flag is set, it means that we do not care about
+** the content of the page at this time.  So do not go to the disk
+** to fetch the content.  Just fill in the content with zeros for now.
+** If in the future we call sqlite3PagerWrite() on this page, that
+** means we have started to be concerned about content and the disk
+** read should occur at that point.
+*/
+int sqlite3BtreeGetPage(
+  BtShared *pBt,       /* The btree */
+  Pgno pgno,           /* Number of the page to fetch */
+  MemPage **ppPage,    /* Return the page in this parameter */
+  int noContent        /* Do not load page content if true */
+){
+  int rc;
+  MemPage *pPage;
+  DbPage *pDbPage;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, noContent);
+  if( rc ) return rc;
+  pPage = (MemPage *)sqlite3PagerGetExtra(pDbPage);
+  pPage->aData = sqlite3PagerGetData(pDbPage);
+  pPage->pDbPage = pDbPage;
+  pPage->pBt = pBt;
+  pPage->pgno = pgno;
+  pPage->hdrOffset = pPage->pgno==1 ? 100 : 0;
+  *ppPage = pPage;
+  return SQLITE_OK;
+}
+
+/*
+** Get a page from the pager and initialize it.  This routine
+** is just a convenience wrapper around separate calls to
+** sqlite3BtreeGetPage() and sqlite3BtreeInitPage().
+*/
+static int getAndInitPage(
+  BtShared *pBt,          /* The database file */
+  Pgno pgno,           /* Number of the page to get */
+  MemPage **ppPage,    /* Write the page pointer here */
+  MemPage *pParent     /* Parent of the page */
+){
+  int rc;
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  if( pgno==0 ){
+    return SQLITE_CORRUPT_BKPT; 
+  }
+  rc = sqlite3BtreeGetPage(pBt, pgno, ppPage, 0);
+  if( rc==SQLITE_OK && (*ppPage)->isInit==0 ){
+    rc = sqlite3BtreeInitPage(*ppPage, pParent);
+  }
+  return rc;
+}
+
+/*
+** Release a MemPage.  This should be called once for each prior
+** call to sqlite3BtreeGetPage.
+*/
+static void releasePage(MemPage *pPage){
+  if( pPage ){
+    assert( pPage->aData );
+    assert( pPage->pBt );
+    assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
+    assert( sqlite3PagerGetData(pPage->pDbPage)==pPage->aData );
+    assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+    sqlite3PagerUnref(pPage->pDbPage);
+  }
+}
+
+/*
+** This routine is called when the reference count for a page
+** reaches zero.  We need to unref the pParent pointer when that
+** happens.
+*/
+static void pageDestructor(DbPage *pData, int pageSize){
+  MemPage *pPage;
+  assert( (pageSize & 7)==0 );
+  pPage = (MemPage *)sqlite3PagerGetExtra(pData);
+  assert( pPage->isInit==0 || sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( pPage->pParent ){
+    MemPage *pParent = pPage->pParent;
+    assert( pParent->pBt==pPage->pBt );
+    pPage->pParent = 0;
+    releasePage(pParent);
+  }
+  pPage->isInit = 0;
+}
+
+/*
+** During a rollback, when the pager reloads information into the cache
+** so that the cache is restored to its original state at the start of
+** the transaction, for each page restored this routine is called.
+**
+** This routine needs to reset the extra data section at the end of the
+** page to agree with the restored data.
+*/
+static void pageReinit(DbPage *pData, int pageSize){
+  MemPage *pPage;
+  assert( (pageSize & 7)==0 );
+  pPage = (MemPage *)sqlite3PagerGetExtra(pData);
+  if( pPage->isInit ){
+    assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+    pPage->isInit = 0;
+    sqlite3BtreeInitPage(pPage, pPage->pParent);
+  }
+}
+
+/*
+** Open a database file.
+** 
+** zFilename is the name of the database file.  If zFilename is NULL
+** a new database with a random name is created.  This randomly named
+** database file will be deleted when sqlite3BtreeClose() is called.
+** If zFilename is ":memory:" then an in-memory database is created
+** that is automatically destroyed when it is closed.
+*/
+int sqlite3BtreeOpen(
+  const char *zFilename,  /* Name of the file containing the BTree database */
+  sqlite3 *pSqlite,       /* Associated database handle */
+  Btree **ppBtree,        /* Pointer to new Btree object written here */
+  int flags,              /* Options */
+  int vfsFlags            /* Flags passed through to sqlite3_vfs.xOpen() */
+){
+  sqlite3_vfs *pVfs;      /* The VFS to use for this btree */
+  BtShared *pBt = 0;      /* Shared part of btree structure */
+  Btree *p;               /* Handle to return */
+  int rc = SQLITE_OK;
+  int nReserve;
+  unsigned char zDbHeader[100];
+
+  /* Set the variable isMemdb to true for an in-memory database, or 
+  ** false for a file-based database. This symbol is only required if
+  ** either of the shared-data or autovacuum features are compiled 
+  ** into the library.
+  */
+#if !defined(SQLITE_OMIT_SHARED_CACHE) || !defined(SQLITE_OMIT_AUTOVACUUM)
+  #ifdef SQLITE_OMIT_MEMORYDB
+    const int isMemdb = 0;
+  #else
+    const int isMemdb = zFilename && !strcmp(zFilename, ":memory:");
+  #endif
+#endif
+
+  assert( pSqlite!=0 );
+  assert( sqlite3_mutex_held(pSqlite->mutex) );
+
+  pVfs = pSqlite->pVfs;
+  p = sqlite3MallocZero(sizeof(Btree));
+  if( !p ){
+    return SQLITE_NOMEM;
+  }
+  p->inTrans = TRANS_NONE;
+  p->pSqlite = pSqlite;
+
+#if !defined(SQLITE_OMIT_SHARED_CACHE) && !defined(SQLITE_OMIT_DISKIO)
+  /*
+  ** If this Btree is a candidate for shared cache, try to find an
+  ** existing BtShared object that we can share with
+  */
+  if( (flags & BTREE_PRIVATE)==0
+   && isMemdb==0
+   && (pSqlite->flags & SQLITE_Vtab)==0
+   && zFilename && zFilename[0]
+  ){
+    if( sqlite3SharedCacheEnabled ){
+      int nFullPathname = pVfs->mxPathname+1;
+      char *zFullPathname = (char *)sqlite3_malloc(nFullPathname);
+      sqlite3_mutex *mutexShared;
+      p->sharable = 1;
+      if( pSqlite ){
+        pSqlite->flags |= SQLITE_SharedCache;
+      }
+      if( !zFullPathname ){
+        sqlite3_free(p);
+        return SQLITE_NOMEM;
+      }
+      sqlite3OsFullPathname(pVfs, zFilename, nFullPathname, zFullPathname);
+      mutexShared = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER);
+      sqlite3_mutex_enter(mutexShared);
+      for(pBt=sqlite3SharedCacheList; pBt; pBt=pBt->pNext){
+        assert( pBt->nRef>0 );
+        if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt->pPager))
+                 && sqlite3PagerVfs(pBt->pPager)==pVfs ){
+          p->pBt = pBt;
+          pBt->nRef++;
+          break;
+        }
+      }
+      sqlite3_mutex_leave(mutexShared);
+      sqlite3_free(zFullPathname);
+    }
+#ifdef SQLITE_DEBUG
+    else{
+      /* In debug mode, we mark all persistent databases as sharable
+      ** even when they are not.  This exercises the locking code and
+      ** gives more opportunity for asserts(sqlite3_mutex_held())
+      ** statements to find locking problems.
+      */
+      p->sharable = 1;
+    }
+#endif
+  }
+#endif
+  if( pBt==0 ){
+    /*
+    ** The following asserts make sure that structures used by the btree are
+    ** the right size.  This is to guard against size changes that result
+    ** when compiling on a different architecture.
+    */
+    assert( sizeof(i64)==8 || sizeof(i64)==4 );
+    assert( sizeof(u64)==8 || sizeof(u64)==4 );
+    assert( sizeof(u32)==4 );
+    assert( sizeof(u16)==2 );
+    assert( sizeof(Pgno)==4 );
+  
+    pBt = sqlite3MallocZero( sizeof(*pBt) );
+    if( pBt==0 ){
+      rc = SQLITE_NOMEM;
+      goto btree_open_out;
+    }
+    rc = sqlite3PagerOpen(pVfs, &pBt->pPager, zFilename,
+                          EXTRA_SIZE, flags, vfsFlags);
+    if( rc==SQLITE_OK ){
+      rc = sqlite3PagerReadFileheader(pBt->pPager,sizeof(zDbHeader),zDbHeader);
+    }
+    if( rc!=SQLITE_OK ){
+      goto btree_open_out;
+    }
+    p->pBt = pBt;
+  
+    sqlite3PagerSetDestructor(pBt->pPager, pageDestructor);
+    sqlite3PagerSetReiniter(pBt->pPager, pageReinit);
+    pBt->pCursor = 0;
+    pBt->pPage1 = 0;
+    pBt->readOnly = sqlite3PagerIsreadonly(pBt->pPager);
+    pBt->pageSize = get2byte(&zDbHeader[16]);
+    if( pBt->pageSize<512 || pBt->pageSize>SQLITE_MAX_PAGE_SIZE
+         || ((pBt->pageSize-1)&pBt->pageSize)!=0 ){
+      pBt->pageSize = 0;
+      sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize);
+      pBt->maxEmbedFrac = 64;   /* 25% */
+      pBt->minEmbedFrac = 32;   /* 12.5% */
+      pBt->minLeafFrac = 32;    /* 12.5% */
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      /* If the magic name ":memory:" will create an in-memory database, then
+      ** leave the autoVacuum mode at 0 (do not auto-vacuum), even if
+      ** SQLITE_DEFAULT_AUTOVACUUM is true. On the other hand, if
+      ** SQLITE_OMIT_MEMORYDB has been defined, then ":memory:" is just a
+      ** regular file-name. In this case the auto-vacuum applies as per normal.
+      */
+      if( zFilename && !isMemdb ){
+        pBt->autoVacuum = (SQLITE_DEFAULT_AUTOVACUUM ? 1 : 0);
+        pBt->incrVacuum = (SQLITE_DEFAULT_AUTOVACUUM==2 ? 1 : 0);
+      }
+#endif
+      nReserve = 0;
+    }else{
+      nReserve = zDbHeader[20];
+      pBt->maxEmbedFrac = zDbHeader[21];
+      pBt->minEmbedFrac = zDbHeader[22];
+      pBt->minLeafFrac = zDbHeader[23];
+      pBt->pageSizeFixed = 1;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      pBt->autoVacuum = (get4byte(&zDbHeader[36 + 4*4])?1:0);
+      pBt->incrVacuum = (get4byte(&zDbHeader[36 + 7*4])?1:0);
+#endif
+    }
+    pBt->usableSize = pBt->pageSize - nReserve;
+    assert( (pBt->pageSize & 7)==0 );  /* 8-byte alignment of pageSize */
+    sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize);
+   
+#if !defined(SQLITE_OMIT_SHARED_CACHE) && !defined(SQLITE_OMIT_DISKIO)
+    /* Add the new BtShared object to the linked list sharable BtShareds.
+    */
+    if( p->sharable ){
+      sqlite3_mutex *mutexShared;
+      pBt->nRef = 1;
+      mutexShared = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER);
+      if( SQLITE_THREADSAFE ){
+        pBt->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
+        if( pBt->mutex==0 ){
+          rc = SQLITE_NOMEM;
+          pSqlite->mallocFailed = 0;
+          goto btree_open_out;
+        }
+      }
+      sqlite3_mutex_enter(mutexShared);
+      pBt->pNext = sqlite3SharedCacheList;
+      sqlite3SharedCacheList = pBt;
+      sqlite3_mutex_leave(mutexShared);
+    }
+#endif
+  }
+
+#if !defined(SQLITE_OMIT_SHARED_CACHE) && !defined(SQLITE_OMIT_DISKIO)
+  /* If the new Btree uses a sharable pBtShared, then link the new
+  ** Btree into the list of all sharable Btrees for the same connection.
+  ** The list is kept in ascending order by pBt address.
+  */
+  if( p->sharable ){
+    int i;
+    Btree *pSib;
+    for(i=0; i<pSqlite->nDb; i++){
+      if( (pSib = pSqlite->aDb[i].pBt)!=0 && pSib->sharable ){
+        while( pSib->pPrev ){ pSib = pSib->pPrev; }
+        if( p->pBt<pSib->pBt ){
+          p->pNext = pSib;
+          p->pPrev = 0;
+          pSib->pPrev = p;
+        }else{
+          while( pSib->pNext && pSib->pNext->pBt<p->pBt ){
+            pSib = pSib->pNext;
+          }
+          p->pNext = pSib->pNext;
+          p->pPrev = pSib;
+          if( p->pNext ){
+            p->pNext->pPrev = p;
+          }
+          pSib->pNext = p;
+        }
+        break;
+      }
+    }
+  }
+#endif
+  *ppBtree = p;
+
+btree_open_out:
+  if( rc!=SQLITE_OK ){
+    if( pBt && pBt->pPager ){
+      sqlite3PagerClose(pBt->pPager);
+    }
+    sqlite3_free(pBt);
+    sqlite3_free(p);
+    *ppBtree = 0;
+  }
+  return rc;
+}
+
+/*
+** Decrement the BtShared.nRef counter.  When it reaches zero,
+** remove the BtShared structure from the sharing list.  Return
+** true if the BtShared.nRef counter reaches zero and return
+** false if it is still positive.
+*/
+static int removeFromSharingList(BtShared *pBt){
+#ifndef SQLITE_OMIT_SHARED_CACHE
+  sqlite3_mutex *pMaster;
+  BtShared *pList;
+  int removed = 0;
+
+  assert( sqlite3_mutex_notheld(pBt->mutex) );
+  pMaster = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER);
+  sqlite3_mutex_enter(pMaster);
+  pBt->nRef--;
+  if( pBt->nRef<=0 ){
+    if( sqlite3SharedCacheList==pBt ){
+      sqlite3SharedCacheList = pBt->pNext;
+    }else{
+      pList = sqlite3SharedCacheList;
+      while( pList && pList->pNext!=pBt ){
+        pList=pList->pNext;
+      }
+      if( pList ){
+        pList->pNext = pBt->pNext;
+      }
+    }
+    if( SQLITE_THREADSAFE ){
+      sqlite3_mutex_free(pBt->mutex);
+    }
+    removed = 1;
+  }
+  sqlite3_mutex_leave(pMaster);
+  return removed;
+#else
+  return 1;
+#endif
+}
+
+/*
+** Close an open database and invalidate all cursors.
+*/
+int sqlite3BtreeClose(Btree *p){
+  BtShared *pBt = p->pBt;
+  BtCursor *pCur;
+
+  /* Close all cursors opened via this handle.  */
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );
+  sqlite3BtreeEnter(p);
+  pCur = pBt->pCursor;
+  while( pCur ){
+    BtCursor *pTmp = pCur;
+    pCur = pCur->pNext;
+    if( pTmp->pBtree==p ){
+      sqlite3BtreeCloseCursor(pTmp);
+    }
+  }
+
+  /* Rollback any active transaction and free the handle structure.
+  ** The call to sqlite3BtreeRollback() drops any table-locks held by
+  ** this handle.
+  */
+  sqlite3BtreeRollback(p);
+  sqlite3BtreeLeave(p);
+
+  /* If there are still other outstanding references to the shared-btree
+  ** structure, return now. The remainder of this procedure cleans 
+  ** up the shared-btree.
+  */
+  assert( p->wantToLock==0 && p->locked==0 );
+  if( !p->sharable || removeFromSharingList(pBt) ){
+    /* The pBt is no longer on the sharing list, so we can access
+    ** it without having to hold the mutex.
+    **
+    ** Clean out and delete the BtShared object.
+    */
+    assert( !pBt->pCursor );
+    sqlite3PagerClose(pBt->pPager);
+    if( pBt->xFreeSchema && pBt->pSchema ){
+      pBt->xFreeSchema(pBt->pSchema);
+    }
+    sqlite3_free(pBt->pSchema);
+    sqlite3_free(pBt);
+  }
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+  assert( p->wantToLock==0 );
+  assert( p->locked==0 );
+  if( p->pPrev ) p->pPrev->pNext = p->pNext;
+  if( p->pNext ) p->pNext->pPrev = p->pPrev;
+#endif
+
+  sqlite3_free(p);
+  return SQLITE_OK;
+}
+
+/*
+** Change the busy handler callback function.
+*/
+int sqlite3BtreeSetBusyHandler(Btree *p, BusyHandler *pHandler){
+  BtShared *pBt = p->pBt;
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );
+  sqlite3BtreeEnter(p);
+  pBt->pBusyHandler = pHandler;
+  sqlite3PagerSetBusyhandler(pBt->pPager, pHandler);
+  sqlite3BtreeLeave(p);
+  return SQLITE_OK;
+}
+
+/*
+** Change the limit on the number of pages allowed in the cache.
+**
+** The maximum number of cache pages is set to the absolute
+** value of mxPage.  If mxPage is negative, the pager will
+** operate asynchronously - it will not stop to do fsync()s
+** to insure data is written to the disk surface before
+** continuing.  Transactions still work if synchronous is off,
+** and the database cannot be corrupted if this program
+** crashes.  But if the operating system crashes or there is
+** an abrupt power failure when synchronous is off, the database
+** could be left in an inconsistent and unrecoverable state.
+** Synchronous is on by default so database corruption is not
+** normally a worry.
+*/
+int sqlite3BtreeSetCacheSize(Btree *p, int mxPage){
+  BtShared *pBt = p->pBt;
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );
+  sqlite3BtreeEnter(p);
+  sqlite3PagerSetCachesize(pBt->pPager, mxPage);
+  sqlite3BtreeLeave(p);
+  return SQLITE_OK;
+}
+
+/*
+** Change the way data is synced to disk in order to increase or decrease
+** how well the database resists damage due to OS crashes and power
+** failures.  Level 1 is the same as asynchronous (no syncs() occur and
+** there is a high probability of damage)  Level 2 is the default.  There
+** is a very low but non-zero probability of damage.  Level 3 reduces the
+** probability of damage to near zero but with a write performance reduction.
+*/
+#ifndef SQLITE_OMIT_PAGER_PRAGMAS
+int sqlite3BtreeSetSafetyLevel(Btree *p, int level, int fullSync){
+  BtShared *pBt = p->pBt;
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );
+  sqlite3BtreeEnter(p);
+  sqlite3PagerSetSafetyLevel(pBt->pPager, level, fullSync);
+  sqlite3BtreeLeave(p);
+  return SQLITE_OK;
+}
+#endif
+
+/*
+** Return TRUE if the given btree is set to safety level 1.  In other
+** words, return TRUE if no sync() occurs on the disk files.
+*/
+int sqlite3BtreeSyncDisabled(Btree *p){
+  BtShared *pBt = p->pBt;
+  int rc;
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );  
+  sqlite3BtreeEnter(p);
+  assert( pBt && pBt->pPager );
+  rc = sqlite3PagerNosync(pBt->pPager);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+#if !defined(SQLITE_OMIT_PAGER_PRAGMAS) || !defined(SQLITE_OMIT_VACUUM)
+/*
+** Change the default pages size and the number of reserved bytes per page.
+**
+** The page size must be a power of 2 between 512 and 65536.  If the page
+** size supplied does not meet this constraint then the page size is not
+** changed.
+**
+** Page sizes are constrained to be a power of two so that the region
+** of the database file used for locking (beginning at PENDING_BYTE,
+** the first byte past the 1GB boundary, 0x40000000) needs to occur
+** at the beginning of a page.
+**
+** If parameter nReserve is less than zero, then the number of reserved
+** bytes per page is left unchanged.
+*/
+int sqlite3BtreeSetPageSize(Btree *p, int pageSize, int nReserve){
+  int rc = SQLITE_OK;
+  BtShared *pBt = p->pBt;
+  sqlite3BtreeEnter(p);
+  if( pBt->pageSizeFixed ){
+    sqlite3BtreeLeave(p);
+    return SQLITE_READONLY;
+  }
+  if( nReserve<0 ){
+    nReserve = pBt->pageSize - pBt->usableSize;
+  }
+  if( pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE &&
+        ((pageSize-1)&pageSize)==0 ){
+    assert( (pageSize & 7)==0 );
+    assert( !pBt->pPage1 && !pBt->pCursor );
+    pBt->pageSize = pageSize;
+    rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize);
+  }
+  pBt->usableSize = pBt->pageSize - nReserve;
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Return the currently defined page size
+*/
+int sqlite3BtreeGetPageSize(Btree *p){
+  return p->pBt->pageSize;
+}
+int sqlite3BtreeGetReserve(Btree *p){
+  int n;
+  sqlite3BtreeEnter(p);
+  n = p->pBt->pageSize - p->pBt->usableSize;
+  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){
+  int n;
+  sqlite3BtreeEnter(p);
+  n = sqlite3PagerMaxPageCount(p->pBt->pPager, mxPage);
+  sqlite3BtreeLeave(p);
+  return n;
+}
+#endif /* !defined(SQLITE_OMIT_PAGER_PRAGMAS) || !defined(SQLITE_OMIT_VACUUM) */
+
+/*
+** 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 sqlite3BtreeSetAutoVacuum(Btree *p, int autoVacuum){
+#ifdef SQLITE_OMIT_AUTOVACUUM
+  return SQLITE_READONLY;
+#else
+  BtShared *pBt = p->pBt;
+  int rc = SQLITE_OK;
+  int av = (autoVacuum?1:0);
+
+  sqlite3BtreeEnter(p);
+  if( pBt->pageSizeFixed && av!=pBt->autoVacuum ){
+    rc = SQLITE_READONLY;
+  }else{
+    pBt->autoVacuum = av;
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+#endif
+}
+
+/*
+** Return the value of the 'auto-vacuum' property. If auto-vacuum is 
+** enabled 1 is returned. Otherwise 0.
+*/
+int sqlite3BtreeGetAutoVacuum(Btree *p){
+#ifdef SQLITE_OMIT_AUTOVACUUM
+  return BTREE_AUTOVACUUM_NONE;
+#else
+  int rc;
+  sqlite3BtreeEnter(p);
+  rc = (
+    (!p->pBt->autoVacuum)?BTREE_AUTOVACUUM_NONE:
+    (!p->pBt->incrVacuum)?BTREE_AUTOVACUUM_FULL:
+    BTREE_AUTOVACUUM_INCR
+  );
+  sqlite3BtreeLeave(p);
+  return rc;
+#endif
+}
+
+
+/*
+** Get a reference to pPage1 of the database file.  This will
+** also acquire a readlock on that file.
+**
+** SQLITE_OK is returned on success.  If the file is not a
+** well-formed database file, then SQLITE_CORRUPT is returned.
+** SQLITE_BUSY is returned if the database is locked.  SQLITE_NOMEM
+** is returned if we run out of memory. 
+*/
+static int lockBtree(BtShared *pBt){
+  int rc, pageSize;
+  MemPage *pPage1;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  if( pBt->pPage1 ) return SQLITE_OK;
+  rc = sqlite3BtreeGetPage(pBt, 1, &pPage1, 0);
+  if( rc!=SQLITE_OK ) return rc;
+  
+
+  /* Do some checking to help insure the file we opened really is
+  ** a valid database file. 
+  */
+  rc = SQLITE_NOTADB;
+  if( sqlite3PagerPagecount(pBt->pPager)>0 ){
+    u8 *page1 = pPage1->aData;
+    if( memcmp(page1, zMagicHeader, 16)!=0 ){
+      goto page1_init_failed;
+    }
+    if( page1[18]>1 ){
+      pBt->readOnly = 1;
+    }
+    if( page1[19]>1 ){
+      goto page1_init_failed;
+    }
+    pageSize = get2byte(&page1[16]);
+    if( ((pageSize-1)&pageSize)!=0 || pageSize<512 ||
+        (SQLITE_MAX_PAGE_SIZE<32768 && pageSize>SQLITE_MAX_PAGE_SIZE)
+    ){
+      goto page1_init_failed;
+    }
+    assert( (pageSize & 7)==0 );
+    pBt->pageSize = pageSize;
+    pBt->usableSize = pageSize - page1[20];
+    if( pBt->usableSize<500 ){
+      goto page1_init_failed;
+    }
+    pBt->maxEmbedFrac = page1[21];
+    pBt->minEmbedFrac = page1[22];
+    pBt->minLeafFrac = page1[23];
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    pBt->autoVacuum = (get4byte(&page1[36 + 4*4])?1:0);
+    pBt->incrVacuum = (get4byte(&page1[36 + 7*4])?1:0);
+#endif
+  }
+
+  /* maxLocal is the maximum amount of payload to store locally for
+  ** a cell.  Make sure it is small enough so that at least minFanout
+  ** cells can will fit on one page.  We assume a 10-byte page header.
+  ** Besides the payload, the cell must store:
+  **     2-byte pointer to the cell
+  **     4-byte child pointer
+  **     9-byte nKey value
+  **     4-byte nData value
+  **     4-byte overflow page pointer
+  ** So a cell consists of a 2-byte poiner, a header which is as much as
+  ** 17 bytes long, 0 to N bytes of payload, and an optional 4 byte overflow
+  ** page pointer.
+  */
+  pBt->maxLocal = (pBt->usableSize-12)*pBt->maxEmbedFrac/255 - 23;
+  pBt->minLocal = (pBt->usableSize-12)*pBt->minEmbedFrac/255 - 23;
+  pBt->maxLeaf = pBt->usableSize - 35;
+  pBt->minLeaf = (pBt->usableSize-12)*pBt->minLeafFrac/255 - 23;
+  if( pBt->minLocal>pBt->maxLocal || pBt->maxLocal<0 ){
+    goto page1_init_failed;
+  }
+  assert( pBt->maxLeaf + 23 <= MX_CELL_SIZE(pBt) );
+  pBt->pPage1 = pPage1;
+  return SQLITE_OK;
+
+page1_init_failed:
+  releasePage(pPage1);
+  pBt->pPage1 = 0;
+  return rc;
+}
+
+/*
+** This routine works like lockBtree() except that it also invokes the
+** busy callback if there is lock contention.
+*/
+static int lockBtreeWithRetry(Btree *pRef){
+  int rc = SQLITE_OK;
+
+  assert( sqlite3BtreeHoldsMutex(pRef) );
+  if( pRef->inTrans==TRANS_NONE ){
+    u8 inTransaction = pRef->pBt->inTransaction;
+    btreeIntegrity(pRef);
+    rc = sqlite3BtreeBeginTrans(pRef, 0);
+    pRef->pBt->inTransaction = inTransaction;
+    pRef->inTrans = TRANS_NONE;
+    if( rc==SQLITE_OK ){
+      pRef->pBt->nTransaction--;
+    }
+    btreeIntegrity(pRef);
+  }
+  return rc;
+}
+       
+
+/*
+** If there are no outstanding cursors and we are not in the middle
+** of a transaction but there is a read lock on the database, then
+** this routine unrefs the first page of the database file which 
+** has the effect of releasing the read lock.
+**
+** If there are any outstanding cursors, this routine is a no-op.
+**
+** If there is a transaction in progress, this routine is a no-op.
+*/
+static void unlockBtreeIfUnused(BtShared *pBt){
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  if( pBt->inTransaction==TRANS_NONE && pBt->pCursor==0 && pBt->pPage1!=0 ){
+    if( sqlite3PagerRefcount(pBt->pPager)>=1 ){
+      if( pBt->pPage1->aData==0 ){
+        MemPage *pPage = pBt->pPage1;
+        pPage->aData = sqlite3PagerGetData(pPage->pDbPage);
+        pPage->pBt = pBt;
+        pPage->pgno = 1;
+      }
+      releasePage(pBt->pPage1);
+    }
+    pBt->pPage1 = 0;
+    pBt->inStmt = 0;
+  }
+}
+
+/*
+** Create a new database by initializing the first page of the
+** file.
+*/
+static int newDatabase(BtShared *pBt){
+  MemPage *pP1;
+  unsigned char *data;
+  int rc;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  if( sqlite3PagerPagecount(pBt->pPager)>0 ) return SQLITE_OK;
+  pP1 = pBt->pPage1;
+  assert( pP1!=0 );
+  data = pP1->aData;
+  rc = sqlite3PagerWrite(pP1->pDbPage);
+  if( rc ) return rc;
+  memcpy(data, zMagicHeader, sizeof(zMagicHeader));
+  assert( sizeof(zMagicHeader)==16 );
+  put2byte(&data[16], pBt->pageSize);
+  data[18] = 1;
+  data[19] = 1;
+  data[20] = pBt->pageSize - pBt->usableSize;
+  data[21] = pBt->maxEmbedFrac;
+  data[22] = pBt->minEmbedFrac;
+  data[23] = pBt->minLeafFrac;
+  memset(&data[24], 0, 100-24);
+  zeroPage(pP1, PTF_INTKEY|PTF_LEAF|PTF_LEAFDATA );
+  pBt->pageSizeFixed = 1;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  assert( pBt->autoVacuum==1 || pBt->autoVacuum==0 );
+  assert( pBt->incrVacuum==1 || pBt->incrVacuum==0 );
+  put4byte(&data[36 + 4*4], pBt->autoVacuum);
+  put4byte(&data[36 + 7*4], pBt->incrVacuum);
+#endif
+  return SQLITE_OK;
+}
+
+/*
+** Attempt to start a new transaction. A write-transaction
+** is started if the second argument is nonzero, otherwise a read-
+** transaction.  If the second argument is 2 or more and exclusive
+** transaction is started, meaning that no other process is allowed
+** to access the database.  A preexisting transaction may not be
+** upgraded to exclusive by calling this routine a second time - the
+** exclusivity flag only works for a new transaction.
+**
+** A write-transaction must be started before attempting any 
+** changes to the database.  None of the following routines 
+** will work unless a transaction is started first:
+**
+**      sqlite3BtreeCreateTable()
+**      sqlite3BtreeCreateIndex()
+**      sqlite3BtreeClearTable()
+**      sqlite3BtreeDropTable()
+**      sqlite3BtreeInsert()
+**      sqlite3BtreeDelete()
+**      sqlite3BtreeUpdateMeta()
+**
+** If an initial attempt to acquire the lock fails because of lock contention
+** and the database was previously unlocked, then invoke the busy handler
+** if there is one.  But if there was previously a read-lock, do not
+** invoke the busy handler - just return SQLITE_BUSY.  SQLITE_BUSY is 
+** returned when there is already a read-lock in order to avoid a deadlock.
+**
+** Suppose there are two processes A and B.  A has a read lock and B has
+** a reserved lock.  B tries to promote to exclusive but is blocked because
+** of A's read lock.  A tries to promote to reserved but is blocked by B.
+** One or the other of the two processes must give way or there can be
+** no progress.  By returning SQLITE_BUSY and not invoking the busy callback
+** when A already has a read lock, we encourage A to give up and let B
+** proceed.
+*/
+int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
+  BtShared *pBt = p->pBt;
+  int rc = SQLITE_OK;
+
+  sqlite3BtreeEnter(p);
+  btreeIntegrity(p);
+
+  /* If the btree is already in a write-transaction, or it
+  ** is already in a read-transaction and a read-transaction
+  ** is requested, this is a no-op.
+  */
+  if( p->inTrans==TRANS_WRITE || (p->inTrans==TRANS_READ && !wrflag) ){
+    goto trans_begun;
+  }
+
+  /* Write transactions are not possible on a read-only database */
+  if( pBt->readOnly && wrflag ){
+    rc = SQLITE_READONLY;
+    goto trans_begun;
+  }
+
+  /* If another database handle has already opened a write transaction 
+  ** on this shared-btree structure and a second write transaction is
+  ** requested, return SQLITE_BUSY.
+  */
+  if( pBt->inTransaction==TRANS_WRITE && wrflag ){
+    rc = SQLITE_BUSY;
+    goto trans_begun;
+  }
+
+  do {
+    if( pBt->pPage1==0 ){
+      rc = lockBtree(pBt);
+    }
+
+    if( rc==SQLITE_OK && wrflag ){
+      if( pBt->readOnly ){
+        rc = SQLITE_READONLY;
+      }else{
+        rc = sqlite3PagerBegin(pBt->pPage1->pDbPage, wrflag>1);
+        if( rc==SQLITE_OK ){
+          rc = newDatabase(pBt);
+        }
+      }
+    }
+  
+    if( rc==SQLITE_OK ){
+      if( wrflag ) pBt->inStmt = 0;
+    }else{
+      unlockBtreeIfUnused(pBt);
+    }
+  }while( rc==SQLITE_BUSY && pBt->inTransaction==TRANS_NONE &&
+          sqlite3InvokeBusyHandler(pBt->pBusyHandler) );
+
+  if( rc==SQLITE_OK ){
+    if( p->inTrans==TRANS_NONE ){
+      pBt->nTransaction++;
+    }
+    p->inTrans = (wrflag?TRANS_WRITE:TRANS_READ);
+    if( p->inTrans>pBt->inTransaction ){
+      pBt->inTransaction = p->inTrans;
+    }
+  }
+
+
+trans_begun:
+  btreeIntegrity(p);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+
+/*
+** Set the pointer-map entries for all children of page pPage. Also, if
+** pPage contains cells that point to overflow pages, set the pointer
+** map entries for the overflow pages as well.
+*/
+static int setChildPtrmaps(MemPage *pPage){
+  int i;                             /* Counter variable */
+  int nCell;                         /* Number of cells in page pPage */
+  int rc;                            /* Return code */
+  BtShared *pBt = pPage->pBt;
+  int isInitOrig = pPage->isInit;
+  Pgno pgno = pPage->pgno;
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  rc = sqlite3BtreeInitPage(pPage, pPage->pParent);
+  if( rc!=SQLITE_OK ){
+    goto set_child_ptrmaps_out;
+  }
+  nCell = pPage->nCell;
+
+  for(i=0; i<nCell; i++){
+    u8 *pCell = findCell(pPage, i);
+
+    rc = ptrmapPutOvflPtr(pPage, pCell);
+    if( rc!=SQLITE_OK ){
+      goto set_child_ptrmaps_out;
+    }
+
+    if( !pPage->leaf ){
+      Pgno childPgno = get4byte(pCell);
+      rc = ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno);
+      if( rc!=SQLITE_OK ) goto set_child_ptrmaps_out;
+    }
+  }
+
+  if( !pPage->leaf ){
+    Pgno childPgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
+    rc = ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno);
+  }
+
+set_child_ptrmaps_out:
+  pPage->isInit = isInitOrig;
+  return rc;
+}
+
+/*
+** Somewhere on pPage, which is guarenteed to be a btree page, not an overflow
+** page, is a pointer to page iFrom. Modify this pointer so that it points to
+** iTo. Parameter eType describes the type of pointer to be modified, as 
+** follows:
+**
+** PTRMAP_BTREE:     pPage is a btree-page. The pointer points at a child 
+**                   page of pPage.
+**
+** PTRMAP_OVERFLOW1: pPage is a btree-page. The pointer points at an overflow
+**                   page pointed to by one of the cells on pPage.
+**
+** PTRMAP_OVERFLOW2: pPage is an overflow-page. The pointer points at the next
+**                   overflow page in the list.
+*/
+static int modifyPagePointer(MemPage *pPage, Pgno iFrom, Pgno iTo, u8 eType){
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( eType==PTRMAP_OVERFLOW2 ){
+    /* The pointer is always the first 4 bytes of the page in this case.  */
+    if( get4byte(pPage->aData)!=iFrom ){
+      return SQLITE_CORRUPT_BKPT;
+    }
+    put4byte(pPage->aData, iTo);
+  }else{
+    int isInitOrig = pPage->isInit;
+    int i;
+    int nCell;
+
+    sqlite3BtreeInitPage(pPage, 0);
+    nCell = pPage->nCell;
+
+    for(i=0; i<nCell; i++){
+      u8 *pCell = findCell(pPage, i);
+      if( eType==PTRMAP_OVERFLOW1 ){
+        CellInfo info;
+        sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+        if( info.iOverflow ){
+          if( iFrom==get4byte(&pCell[info.iOverflow]) ){
+            put4byte(&pCell[info.iOverflow], iTo);
+            break;
+          }
+        }
+      }else{
+        if( get4byte(pCell)==iFrom ){
+          put4byte(pCell, iTo);
+          break;
+        }
+      }
+    }
+  
+    if( i==nCell ){
+      if( eType!=PTRMAP_BTREE || 
+          get4byte(&pPage->aData[pPage->hdrOffset+8])!=iFrom ){
+        return SQLITE_CORRUPT_BKPT;
+      }
+      put4byte(&pPage->aData[pPage->hdrOffset+8], iTo);
+    }
+
+    pPage->isInit = isInitOrig;
+  }
+  return SQLITE_OK;
+}
+
+
+/*
+** Move the open database page pDbPage to location iFreePage in the 
+** database. The pDbPage reference remains valid.
+*/
+static int relocatePage(
+  BtShared *pBt,           /* Btree */
+  MemPage *pDbPage,        /* Open page to move */
+  u8 eType,                /* Pointer map 'type' entry for pDbPage */
+  Pgno iPtrPage,           /* Pointer map 'page-no' entry for pDbPage */
+  Pgno iFreePage           /* The location to move pDbPage to */
+){
+  MemPage *pPtrPage;   /* The page that contains a pointer to pDbPage */
+  Pgno iDbPage = pDbPage->pgno;
+  Pager *pPager = pBt->pPager;
+  int rc;
+
+  assert( eType==PTRMAP_OVERFLOW2 || eType==PTRMAP_OVERFLOW1 || 
+      eType==PTRMAP_BTREE || eType==PTRMAP_ROOTPAGE );
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  assert( pDbPage->pBt==pBt );
+
+  /* Move page iDbPage from it's current location to page number iFreePage */
+  TRACE(("AUTOVACUUM: Moving %d to free page %d (ptr page %d type %d)\n", 
+      iDbPage, iFreePage, iPtrPage, eType));
+  rc = sqlite3PagerMovepage(pPager, pDbPage->pDbPage, iFreePage);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  pDbPage->pgno = iFreePage;
+
+  /* If pDbPage was a btree-page, then it may have child pages and/or cells
+  ** that point to overflow pages. The pointer map entries for all these
+  ** pages need to be changed.
+  **
+  ** If pDbPage is an overflow page, then the first 4 bytes may store a
+  ** pointer to a subsequent overflow page. If this is the case, then
+  ** the pointer map needs to be updated for the subsequent overflow page.
+  */
+  if( eType==PTRMAP_BTREE || eType==PTRMAP_ROOTPAGE ){
+    rc = setChildPtrmaps(pDbPage);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+  }else{
+    Pgno nextOvfl = get4byte(pDbPage->aData);
+    if( nextOvfl!=0 ){
+      rc = ptrmapPut(pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+    }
+  }
+
+  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
+  ** that it points at iFreePage. Also fix the pointer map entry for
+  ** iPtrPage.
+  */
+  if( eType!=PTRMAP_ROOTPAGE ){
+    rc = sqlite3BtreeGetPage(pBt, iPtrPage, &pPtrPage, 0);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    rc = sqlite3PagerWrite(pPtrPage->pDbPage);
+    if( rc!=SQLITE_OK ){
+      releasePage(pPtrPage);
+      return rc;
+    }
+    rc = modifyPagePointer(pPtrPage, iDbPage, iFreePage, eType);
+    releasePage(pPtrPage);
+    if( rc==SQLITE_OK ){
+      rc = ptrmapPut(pBt, iFreePage, eType, iPtrPage);
+    }
+  }
+  return rc;
+}
+
+/* Forward declaration required by incrVacuumStep(). */
+static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);
+
+/*
+** Perform a single step of an incremental-vacuum. If successful,
+** return SQLITE_OK. If there is no work to do (and therefore no
+** point in calling this function again), return SQLITE_DONE.
+**
+** More specificly, this function attempts to re-organize the 
+** database so that the last page of the file currently in use
+** is no longer in use.
+**
+** If the nFin parameter is non-zero, the implementation assumes
+** that the caller will keep calling incrVacuumStep() until
+** it returns SQLITE_DONE or an error, and that nFin is the
+** number of pages the database file will contain after this 
+** process is complete.
+*/
+static int incrVacuumStep(BtShared *pBt, Pgno nFin){
+  Pgno iLastPg;             /* Last page in the database */
+  Pgno nFreeList;           /* Number of pages still on the free-list */
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  iLastPg = pBt->nTrunc;
+  if( iLastPg==0 ){
+    iLastPg = sqlite3PagerPagecount(pBt->pPager);
+  }
+
+  if( !PTRMAP_ISPAGE(pBt, iLastPg) && iLastPg!=PENDING_BYTE_PAGE(pBt) ){
+    int rc;
+    u8 eType;
+    Pgno iPtrPage;
+
+    nFreeList = get4byte(&pBt->pPage1->aData[36]);
+    if( nFreeList==0 || nFin==iLastPg ){
+      return SQLITE_DONE;
+    }
+
+    rc = ptrmapGet(pBt, iLastPg, &eType, &iPtrPage);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    if( eType==PTRMAP_ROOTPAGE ){
+      return SQLITE_CORRUPT_BKPT;
+    }
+
+    if( eType==PTRMAP_FREEPAGE ){
+      if( nFin==0 ){
+        /* Remove the page from the files free-list. This is not required
+        ** if nFin is non-zero. In that case, the free-list will be
+        ** truncated to zero after this function returns, so it doesn't 
+        ** matter if it still contains some garbage entries.
+        */
+        Pgno iFreePg;
+        MemPage *pFreePg;
+        rc = allocateBtreePage(pBt, &pFreePg, &iFreePg, iLastPg, 1);
+        if( rc!=SQLITE_OK ){
+          return rc;
+        }
+        assert( iFreePg==iLastPg );
+        releasePage(pFreePg);
+      }
+    } else {
+      Pgno iFreePg;             /* Index of free page to move pLastPg to */
+      MemPage *pLastPg;
+
+      rc = sqlite3BtreeGetPage(pBt, iLastPg, &pLastPg, 0);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+
+      /* If nFin is zero, this loop runs exactly once and page pLastPg
+      ** is swapped with the first free page pulled off the free list.
+      **
+      ** On the other hand, if nFin is greater than zero, then keep
+      ** looping until a free-page located within the first nFin pages
+      ** of the file is found.
+      */
+      do {
+        MemPage *pFreePg;
+        rc = allocateBtreePage(pBt, &pFreePg, &iFreePg, 0, 0);
+        if( rc!=SQLITE_OK ){
+          releasePage(pLastPg);
+          return rc;
+        }
+        releasePage(pFreePg);
+      }while( nFin!=0 && iFreePg>nFin );
+      assert( iFreePg<iLastPg );
+      
+      rc = sqlite3PagerWrite(pLastPg->pDbPage);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      } 
+      rc = relocatePage(pBt, pLastPg, eType, iPtrPage, iFreePg);
+      releasePage(pLastPg);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      } 
+    }
+  }
+
+  pBt->nTrunc = iLastPg - 1;
+  while( pBt->nTrunc==PENDING_BYTE_PAGE(pBt)||PTRMAP_ISPAGE(pBt, pBt->nTrunc) ){
+    pBt->nTrunc--;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** A write-transaction must be opened before calling this function.
+** It performs a single unit of work towards an incremental vacuum.
+**
+** If the incremental vacuum is finished after this function has run,
+** SQLITE_DONE is returned. If it is not finished, but no error occured,
+** SQLITE_OK is returned. Otherwise an SQLite error code. 
+*/
+int sqlite3BtreeIncrVacuum(Btree *p){
+  int rc;
+  BtShared *pBt = p->pBt;
+
+  sqlite3BtreeEnter(p);
+  assert( pBt->inTransaction==TRANS_WRITE && p->inTrans==TRANS_WRITE );
+  if( !pBt->autoVacuum ){
+    rc = SQLITE_DONE;
+  }else{
+    invalidateAllOverflowCache(pBt);
+    rc = incrVacuumStep(pBt, 0);
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** This routine is called prior to sqlite3PagerCommit when a transaction
+** is commited for an auto-vacuum database.
+**
+** If SQLITE_OK is returned, then *pnTrunc is set to the number of pages
+** the database file should be truncated to during the commit process. 
+** i.e. the database has been reorganized so that only the first *pnTrunc
+** pages are in use.
+*/
+static int autoVacuumCommit(BtShared *pBt, Pgno *pnTrunc){
+  int rc = SQLITE_OK;
+  Pager *pPager = pBt->pPager;
+#ifndef NDEBUG
+  int nRef = sqlite3PagerRefcount(pPager);
+#endif
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  invalidateAllOverflowCache(pBt);
+  assert(pBt->autoVacuum);
+  if( !pBt->incrVacuum ){
+    Pgno nFin = 0;
+
+    if( pBt->nTrunc==0 ){
+      Pgno nFree;
+      Pgno nPtrmap;
+      const int pgsz = pBt->pageSize;
+      Pgno nOrig = sqlite3PagerPagecount(pBt->pPager);
+
+      if( PTRMAP_ISPAGE(pBt, nOrig) ){
+        return SQLITE_CORRUPT_BKPT;
+      }
+      if( nOrig==PENDING_BYTE_PAGE(pBt) ){
+        nOrig--;
+      }
+      nFree = get4byte(&pBt->pPage1->aData[36]);
+      nPtrmap = (nFree-nOrig+PTRMAP_PAGENO(pBt, nOrig)+pgsz/5)/(pgsz/5);
+      nFin = nOrig - nFree - nPtrmap;
+      if( nOrig>PENDING_BYTE_PAGE(pBt) && nFin<=PENDING_BYTE_PAGE(pBt) ){
+        nFin--;
+      }
+      while( PTRMAP_ISPAGE(pBt, nFin) || nFin==PENDING_BYTE_PAGE(pBt) ){
+        nFin--;
+      }
+    }
+
+    while( rc==SQLITE_OK ){
+      rc = incrVacuumStep(pBt, nFin);
+    }
+    if( rc==SQLITE_DONE ){
+      assert(nFin==0 || pBt->nTrunc==0 || nFin<=pBt->nTrunc);
+      rc = SQLITE_OK;
+      if( pBt->nTrunc ){
+        rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
+        put4byte(&pBt->pPage1->aData[32], 0);
+        put4byte(&pBt->pPage1->aData[36], 0);
+        pBt->nTrunc = nFin;
+      }
+    }
+    if( rc!=SQLITE_OK ){
+      sqlite3PagerRollback(pPager);
+    }
+  }
+
+  if( rc==SQLITE_OK ){
+    *pnTrunc = pBt->nTrunc;
+    pBt->nTrunc = 0;
+  }
+  assert( nRef==sqlite3PagerRefcount(pPager) );
+  return rc;
+}
+
+#endif
+
+/*
+** This routine does the first phase of a two-phase commit.  This routine
+** causes a rollback journal to be created (if it does not already exist)
+** and populated with enough information so that if a power loss occurs
+** the database can be restored to its original state by playing back
+** the journal.  Then the contents of the journal are flushed out to
+** the disk.  After the journal is safely on oxide, the changes to the
+** database are written into the database file and flushed to oxide.
+** At the end of this call, the rollback journal still exists on the
+** disk and we are still holding all locks, so the transaction has not
+** committed.  See sqlite3BtreeCommit() for the second phase of the
+** commit process.
+**
+** This call is a no-op if no write-transaction is currently active on pBt.
+**
+** Otherwise, sync the database file for the btree pBt. zMaster points to
+** the name of a master journal file that should be written into the
+** individual journal file, or is NULL, indicating no master journal file 
+** (single database transaction).
+**
+** When this is called, the master journal should already have been
+** created, populated with this journal pointer and synced to disk.
+**
+** Once this is routine has returned, the only thing required to commit
+** the write-transaction for this database file is to delete the journal.
+*/
+int sqlite3BtreeCommitPhaseOne(Btree *p, const char *zMaster){
+  int rc = SQLITE_OK;
+  if( p->inTrans==TRANS_WRITE ){
+    BtShared *pBt = p->pBt;
+    Pgno nTrunc = 0;
+    sqlite3BtreeEnter(p);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( pBt->autoVacuum ){
+      rc = autoVacuumCommit(pBt, &nTrunc); 
+      if( rc!=SQLITE_OK ){
+        sqlite3BtreeLeave(p);
+        return rc;
+      }
+    }
+#endif
+    rc = sqlite3PagerCommitPhaseOne(pBt->pPager, zMaster, nTrunc);
+    sqlite3BtreeLeave(p);
+  }
+  return rc;
+}
+
+/*
+** Commit the transaction currently in progress.
+**
+** This routine implements the second phase of a 2-phase commit.  The
+** sqlite3BtreeSync() routine does the first phase and should be invoked
+** prior to calling this routine.  The sqlite3BtreeSync() routine did
+** all the work of writing information out to disk and flushing the
+** contents so that they are written onto the disk platter.  All this
+** routine has to do is delete or truncate the rollback journal
+** (which causes the transaction to commit) and drop locks.
+**
+** This will release the write lock on the database file.  If there
+** are no active cursors, it also releases the read lock.
+*/
+int sqlite3BtreeCommitPhaseTwo(Btree *p){
+  BtShared *pBt = p->pBt;
+
+  sqlite3BtreeEnter(p);
+  btreeIntegrity(p);
+
+  /* If the handle has a write-transaction open, commit the shared-btrees 
+  ** transaction and set the shared state to TRANS_READ.
+  */
+  if( p->inTrans==TRANS_WRITE ){
+    int rc;
+    assert( pBt->inTransaction==TRANS_WRITE );
+    assert( pBt->nTransaction>0 );
+    rc = sqlite3PagerCommitPhaseTwo(pBt->pPager);
+    if( rc!=SQLITE_OK ){
+      sqlite3BtreeLeave(p);
+      return rc;
+    }
+    pBt->inTransaction = TRANS_READ;
+    pBt->inStmt = 0;
+  }
+  unlockAllTables(p);
+
+  /* If the handle has any kind of transaction open, decrement the transaction
+  ** count of the shared btree. If the transaction count reaches 0, set
+  ** the shared state to TRANS_NONE. The unlockBtreeIfUnused() call below
+  ** will unlock the pager.
+  */
+  if( p->inTrans!=TRANS_NONE ){
+    pBt->nTransaction--;
+    if( 0==pBt->nTransaction ){
+      pBt->inTransaction = TRANS_NONE;
+    }
+  }
+
+  /* Set the handles current transaction state to TRANS_NONE and unlock
+  ** the pager if this call closed the only read or write transaction.
+  */
+  p->inTrans = TRANS_NONE;
+  unlockBtreeIfUnused(pBt);
+
+  btreeIntegrity(p);
+  sqlite3BtreeLeave(p);
+  return SQLITE_OK;
+}
+
+/*
+** Do both phases of a commit.
+*/
+int sqlite3BtreeCommit(Btree *p){
+  int rc;
+  sqlite3BtreeEnter(p);
+  rc = sqlite3BtreeCommitPhaseOne(p, 0);
+  if( rc==SQLITE_OK ){
+    rc = sqlite3BtreeCommitPhaseTwo(p);
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+#ifndef NDEBUG
+/*
+** Return the number of write-cursors open on this handle. This is for use
+** in assert() expressions, so it is only compiled if NDEBUG is not
+** defined.
+**
+** For the purposes of this routine, a write-cursor is any cursor that
+** is capable of writing to the databse.  That means the cursor was
+** originally opened for writing and the cursor has not be disabled
+** by having its state changed to CURSOR_FAULT.
+*/
+static int countWriteCursors(BtShared *pBt){
+  BtCursor *pCur;
+  int r = 0;
+  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
+    if( pCur->wrFlag && pCur->eState!=CURSOR_FAULT ) r++; 
+  }
+  return r;
+}
+#endif
+
+/*
+** This routine sets the state to CURSOR_FAULT and the error
+** code to errCode for every cursor on BtShared that pBtree
+** references.
+**
+** Every cursor is tripped, including cursors that belong
+** to other database connections that happen to be sharing
+** the cache with pBtree.
+**
+** This routine gets called when a rollback occurs.
+** All cursors using the same cache must be tripped
+** to prevent them from trying to use the btree after
+** the rollback.  The rollback may have deleted tables
+** or moved root pages, so it is not sufficient to
+** save the state of the cursor.  The cursor must be
+** invalidated.
+*/
+void sqlite3BtreeTripAllCursors(Btree *pBtree, int errCode){
+  BtCursor *p;
+  sqlite3BtreeEnter(pBtree);
+  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
+    clearCursorPosition(p);
+    p->eState = CURSOR_FAULT;
+    p->skip = errCode;
+  }
+  sqlite3BtreeLeave(pBtree);
+}
+
+/*
+** Rollback the transaction in progress.  All cursors will be
+** invalided by this operation.  Any attempt to use a cursor
+** that was open at the beginning of this operation will result
+** in an error.
+**
+** This will release the write lock on the database file.  If there
+** are no active cursors, it also releases the read lock.
+*/
+int sqlite3BtreeRollback(Btree *p){
+  int rc;
+  BtShared *pBt = p->pBt;
+  MemPage *pPage1;
+
+  sqlite3BtreeEnter(p);
+  rc = saveAllCursors(pBt, 0, 0);
+#ifndef SQLITE_OMIT_SHARED_CACHE
+  if( rc!=SQLITE_OK ){
+    /* This is a horrible situation. An IO or malloc() error occured whilst
+    ** trying to save cursor positions. If this is an automatic rollback (as
+    ** the result of a constraint, malloc() failure or IO error) then 
+    ** the cache may be internally inconsistent (not contain valid trees) so
+    ** we cannot simply return the error to the caller. Instead, abort 
+    ** all queries that may be using any of the cursors that failed to save.
+    */
+    sqlite3BtreeTripAllCursors(p, rc);
+  }
+#endif
+  btreeIntegrity(p);
+  unlockAllTables(p);
+
+  if( p->inTrans==TRANS_WRITE ){
+    int rc2;
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    pBt->nTrunc = 0;
+#endif
+
+    assert( TRANS_WRITE==pBt->inTransaction );
+    rc2 = sqlite3PagerRollback(pBt->pPager);
+    if( rc2!=SQLITE_OK ){
+      rc = rc2;
+    }
+
+    /* The rollback may have destroyed the pPage1->aData value.  So
+    ** call sqlite3BtreeGetPage() on page 1 again to make
+    ** sure pPage1->aData is set correctly. */
+    if( sqlite3BtreeGetPage(pBt, 1, &pPage1, 0)==SQLITE_OK ){
+      releasePage(pPage1);
+    }
+    assert( countWriteCursors(pBt)==0 );
+    pBt->inTransaction = TRANS_READ;
+  }
+
+  if( p->inTrans!=TRANS_NONE ){
+    assert( pBt->nTransaction>0 );
+    pBt->nTransaction--;
+    if( 0==pBt->nTransaction ){
+      pBt->inTransaction = TRANS_NONE;
+    }
+  }
+
+  p->inTrans = TRANS_NONE;
+  pBt->inStmt = 0;
+  unlockBtreeIfUnused(pBt);
+
+  btreeIntegrity(p);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Start a statement subtransaction.  The subtransaction can
+** can be rolled back independently of the main transaction.
+** You must start a transaction before starting a subtransaction.
+** The subtransaction is ended automatically if the main transaction
+** commits or rolls back.
+**
+** Only one subtransaction may be active at a time.  It is an error to try
+** to start a new subtransaction if another subtransaction is already active.
+**
+** Statement subtransactions are used around individual SQL statements
+** that are contained within a BEGIN...COMMIT block.  If a constraint
+** error occurs within the statement, the effect of that one statement
+** can be rolled back without having to rollback the entire transaction.
+*/
+int sqlite3BtreeBeginStmt(Btree *p){
+  int rc;
+  BtShared *pBt = p->pBt;
+  sqlite3BtreeEnter(p);
+  if( (p->inTrans!=TRANS_WRITE) || pBt->inStmt ){
+    rc = pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }else{
+    assert( pBt->inTransaction==TRANS_WRITE );
+    rc = pBt->readOnly ? SQLITE_OK : sqlite3PagerStmtBegin(pBt->pPager);
+    pBt->inStmt = 1;
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+
+/*
+** Commit the statment subtransaction currently in progress.  If no
+** subtransaction is active, this is a no-op.
+*/
+int sqlite3BtreeCommitStmt(Btree *p){
+  int rc;
+  BtShared *pBt = p->pBt;
+  sqlite3BtreeEnter(p);
+  if( pBt->inStmt && !pBt->readOnly ){
+    rc = sqlite3PagerStmtCommit(pBt->pPager);
+  }else{
+    rc = SQLITE_OK;
+  }
+  pBt->inStmt = 0;
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Rollback the active statement subtransaction.  If no subtransaction
+** is active this routine is a no-op.
+**
+** All cursors will be invalidated by this operation.  Any attempt
+** to use a cursor that was open at the beginning of this operation
+** will result in an error.
+*/
+int sqlite3BtreeRollbackStmt(Btree *p){
+  int rc = SQLITE_OK;
+  BtShared *pBt = p->pBt;
+  sqlite3BtreeEnter(p);
+  if( pBt->inStmt && !pBt->readOnly ){
+    rc = sqlite3PagerStmtRollback(pBt->pPager);
+    assert( countWriteCursors(pBt)==0 );
+    pBt->inStmt = 0;
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Default key comparison function to be used if no comparison function
+** is specified on the sqlite3BtreeCursor() call.
+*/
+static int dfltCompare(
+  void *NotUsed,             /* User data is not used */
+  int n1, const void *p1,    /* First key to compare */
+  int n2, const void *p2     /* Second key to compare */
+){
+  int c;
+  c = memcmp(p1, p2, n1<n2 ? n1 : n2);
+  if( c==0 ){
+    c = n1 - n2;
+  }
+  return c;
+}
+
+/*
+** Create a new cursor for the BTree whose root is on the page
+** iTable.  The act of acquiring a cursor gets a read lock on 
+** the database file.
+**
+** If wrFlag==0, then the cursor can only be used for reading.
+** If wrFlag==1, then the cursor can be used for reading or for
+** writing if other conditions for writing are also met.  These
+** are the conditions that must be met in order for writing to
+** be allowed:
+**
+** 1:  The cursor must have been opened with wrFlag==1
+**
+** 2:  Other database connections that share the same pager cache
+**     but which are not in the READ_UNCOMMITTED state may not have
+**     cursors open with wrFlag==0 on the same table.  Otherwise
+**     the changes made by this write cursor would be visible to
+**     the read cursors in the other database connection.
+**
+** 3:  The database must be writable (not on read-only media)
+**
+** 4:  There must be an active transaction.
+**
+** No checking is done to make sure that page iTable really is the
+** root page of a b-tree.  If it is not, then the cursor acquired
+** will not work correctly.
+**
+** The comparison function must be logically the same for every cursor
+** on a particular table.  Changing the comparison function will result
+** in incorrect operations.  If the comparison function is NULL, a
+** default comparison function is used.  The comparison function is
+** always ignored for INTKEY tables.
+*/
+static int btreeCursor(
+  Btree *p,                                   /* The btree */
+  int iTable,                                 /* Root page of table to open */
+  int wrFlag,                                 /* 1 to write. 0 read-only */
+  int (*xCmp)(void*,int,const void*,int,const void*), /* Key Comparison func */
+  void *pArg,                                 /* First arg to xCompare() */
+  BtCursor **ppCur                            /* Write new cursor here */
+){
+  int rc;
+  BtCursor *pCur;
+  BtShared *pBt = p->pBt;
+
+  assert( sqlite3BtreeHoldsMutex(p) );
+  *ppCur = 0;
+  if( wrFlag ){
+    if( pBt->readOnly ){
+      return SQLITE_READONLY;
+    }
+    if( checkReadLocks(p, iTable, 0) ){
+      return SQLITE_LOCKED;
+    }
+  }
+
+  if( pBt->pPage1==0 ){
+    rc = lockBtreeWithRetry(p);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    if( pBt->readOnly && wrFlag ){
+      return SQLITE_READONLY;
+    }
+  }
+  pCur = sqlite3MallocZero( sizeof(*pCur) );
+  if( pCur==0 ){
+    rc = SQLITE_NOMEM;
+    goto create_cursor_exception;
+  }
+  pCur->pgnoRoot = (Pgno)iTable;
+  if( iTable==1 && sqlite3PagerPagecount(pBt->pPager)==0 ){
+    rc = SQLITE_EMPTY;
+    goto create_cursor_exception;
+  }
+  rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->pPage, 0);
+  if( rc!=SQLITE_OK ){
+    goto create_cursor_exception;
+  }
+
+  /* Now that no other errors can occur, finish filling in the BtCursor
+  ** variables, link the cursor into the BtShared list and set *ppCur (the
+  ** output argument to this function).
+  */
+  pCur->xCompare = xCmp ? xCmp : dfltCompare;
+  pCur->pArg = pArg;
+  pCur->pBtree = p;
+  pCur->pBt = pBt;
+  pCur->wrFlag = wrFlag;
+  pCur->pNext = pBt->pCursor;
+  if( pCur->pNext ){
+    pCur->pNext->pPrev = pCur;
+  }
+  pBt->pCursor = pCur;
+  pCur->eState = CURSOR_INVALID;
+  *ppCur = pCur;
+
+  return SQLITE_OK;
+
+create_cursor_exception:
+  if( pCur ){
+    releasePage(pCur->pPage);
+    sqlite3_free(pCur);
+  }
+  unlockBtreeIfUnused(pBt);
+  return rc;
+}
+int sqlite3BtreeCursor(
+  Btree *p,                                   /* The btree */
+  int iTable,                                 /* Root page of table to open */
+  int wrFlag,                                 /* 1 to write. 0 read-only */
+  int (*xCmp)(void*,int,const void*,int,const void*), /* Key Comparison func */
+  void *pArg,                                 /* First arg to xCompare() */
+  BtCursor **ppCur                            /* Write new cursor here */
+){
+  int rc;
+  sqlite3BtreeEnter(p);
+  rc = btreeCursor(p, iTable, wrFlag, xCmp, pArg, ppCur);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+
+/*
+** Close a cursor.  The read lock on the database file is released
+** when the last cursor is closed.
+*/
+int sqlite3BtreeCloseCursor(BtCursor *pCur){
+  BtShared *pBt = pCur->pBt;
+  Btree *pBtree = pCur->pBtree;
+
+  sqlite3BtreeEnter(pBtree);
+  clearCursorPosition(pCur);
+  if( pCur->pPrev ){
+    pCur->pPrev->pNext = pCur->pNext;
+  }else{
+    pBt->pCursor = pCur->pNext;
+  }
+  if( pCur->pNext ){
+    pCur->pNext->pPrev = pCur->pPrev;
+  }
+  releasePage(pCur->pPage);
+  unlockBtreeIfUnused(pBt);
+  invalidateOverflowCache(pCur);
+  sqlite3_free(pCur);
+  sqlite3BtreeLeave(pBtree);
+  return SQLITE_OK;
+}
+
+/*
+** Make a temporary cursor by filling in the fields of pTempCur.
+** The temporary cursor is not on the cursor list for the Btree.
+*/
+void sqlite3BtreeGetTempCursor(BtCursor *pCur, BtCursor *pTempCur){
+  assert( cursorHoldsMutex(pCur) );
+  memcpy(pTempCur, pCur, sizeof(*pCur));
+  pTempCur->pNext = 0;
+  pTempCur->pPrev = 0;
+  if( pTempCur->pPage ){
+    sqlite3PagerRef(pTempCur->pPage->pDbPage);
+  }
+}
+
+/*
+** Delete a temporary cursor such as was made by the CreateTemporaryCursor()
+** function above.
+*/
+void sqlite3BtreeReleaseTempCursor(BtCursor *pCur){
+  assert( cursorHoldsMutex(pCur) );
+  if( pCur->pPage ){
+    sqlite3PagerUnref(pCur->pPage->pDbPage);
+  }
+}
+
+/*
+** Make sure the BtCursor* given in the argument has a valid
+** BtCursor.info structure.  If it is not already valid, call
+** sqlite3BtreeParseCell() to fill it in.
+**
+** BtCursor.info is a cache of the information in the current cell.
+** Using this cache reduces the number of calls to sqlite3BtreeParseCell().
+**
+** 2007-06-25:  There is a bug in some versions of MSVC that cause the
+** compiler to crash when getCellInfo() is implemented as a macro.
+** But there is a measureable speed advantage to using the macro on gcc
+** (when less compiler optimizations like -Os or -O0 are used and the
+** compiler is not doing agressive inlining.)  So we use a real function
+** for MSVC and a macro for everything else.  Ticket #2457.
+*/
+#ifndef NDEBUG
+  static void assertCellInfo(BtCursor *pCur){
+    CellInfo info;
+    memset(&info, 0, sizeof(info));
+    sqlite3BtreeParseCell(pCur->pPage, pCur->idx, &info);
+    assert( memcmp(&info, &pCur->info, sizeof(info))==0 );
+  }
+#else
+  #define assertCellInfo(x)
+#endif
+#ifdef _MSC_VER
+  /* Use a real function in MSVC to work around bugs in that compiler. */
+  static void getCellInfo(BtCursor *pCur){
+    if( pCur->info.nSize==0 ){
+      sqlite3BtreeParseCell(pCur->pPage, pCur->idx, &pCur->info);
+    }else{
+      assertCellInfo(pCur);
+    }
+  }
+#else /* if not _MSC_VER */
+  /* Use a macro in all other compilers so that the function is inlined */
+#define getCellInfo(pCur)                                               \
+  if( pCur->info.nSize==0 ){                                            \
+    sqlite3BtreeParseCell(pCur->pPage, pCur->idx, &pCur->info);         \
+  }else{                                                                \
+    assertCellInfo(pCur);                                               \
+  }
+#endif /* _MSC_VER */
+
+/*
+** Set *pSize to the size of the buffer needed to hold the value of
+** the key for the current entry.  If the cursor is not pointing
+** to a valid entry, *pSize is set to 0. 
+**
+** For a table with the INTKEY flag set, this routine returns the key
+** itself, not the number of bytes in the key.
+*/
+int sqlite3BtreeKeySize(BtCursor *pCur, i64 *pSize){
+  int rc;
+
+  assert( cursorHoldsMutex(pCur) );
+  rc = restoreOrClearCursorPosition(pCur);
+  if( rc==SQLITE_OK ){
+    assert( pCur->eState==CURSOR_INVALID || pCur->eState==CURSOR_VALID );
+    if( pCur->eState==CURSOR_INVALID ){
+      *pSize = 0;
+    }else{
+      getCellInfo(pCur);
+      *pSize = pCur->info.nKey;
+    }
+  }
+  return rc;
+}
+
+/*
+** Set *pSize to the number of bytes of data in the entry the
+** cursor currently points to.  Always return SQLITE_OK.
+** Failure is not possible.  If the cursor is not currently
+** pointing to an entry (which can happen, for example, if
+** the database is empty) then *pSize is set to 0.
+*/
+int sqlite3BtreeDataSize(BtCursor *pCur, u32 *pSize){
+  int rc;
+
+  assert( cursorHoldsMutex(pCur) );
+  rc = restoreOrClearCursorPosition(pCur);
+  if( rc==SQLITE_OK ){
+    assert( pCur->eState==CURSOR_INVALID || pCur->eState==CURSOR_VALID );
+    if( pCur->eState==CURSOR_INVALID ){
+      /* Not pointing at a valid entry - set *pSize to 0. */
+      *pSize = 0;
+    }else{
+      getCellInfo(pCur);
+      *pSize = pCur->info.nData;
+    }
+  }
+  return rc;
+}
+
+/*
+** Given the page number of an overflow page in the database (parameter
+** ovfl), this function finds the page number of the next page in the 
+** linked list of overflow pages. If possible, it uses the auto-vacuum
+** pointer-map data instead of reading the content of page ovfl to do so. 
+**
+** If an error occurs an SQLite error code is returned. Otherwise:
+**
+** Unless pPgnoNext is NULL, the page number of the next overflow 
+** page in the linked list is written to *pPgnoNext. If page ovfl
+** is the last page in it's linked list, *pPgnoNext is set to zero. 
+**
+** If ppPage is not NULL, *ppPage is set to the MemPage* handle
+** for page ovfl. The underlying pager page may have been requested
+** with the noContent flag set, so the page data accessable via
+** this handle may not be trusted.
+*/
+static int getOverflowPage(
+  BtShared *pBt, 
+  Pgno ovfl,                   /* Overflow page */
+  MemPage **ppPage,            /* OUT: MemPage handle */
+  Pgno *pPgnoNext              /* OUT: Next overflow page number */
+){
+  Pgno next = 0;
+  int rc;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  /* One of these must not be NULL. Otherwise, why call this function? */
+  assert(ppPage || pPgnoNext);
+
+  /* If pPgnoNext is NULL, then this function is being called to obtain
+  ** a MemPage* reference only. No page-data is required in this case.
+  */
+  if( !pPgnoNext ){
+    return sqlite3BtreeGetPage(pBt, ovfl, ppPage, 1);
+  }
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  /* Try to find the next page in the overflow list using the
+  ** autovacuum pointer-map pages. Guess that the next page in 
+  ** the overflow list is page number (ovfl+1). If that guess turns 
+  ** out to be wrong, fall back to loading the data of page 
+  ** number ovfl to determine the next page number.
+  */
+  if( pBt->autoVacuum ){
+    Pgno pgno;
+    Pgno iGuess = ovfl+1;
+    u8 eType;
+
+    while( PTRMAP_ISPAGE(pBt, iGuess) || iGuess==PENDING_BYTE_PAGE(pBt) ){
+      iGuess++;
+    }
+
+    if( iGuess<=sqlite3PagerPagecount(pBt->pPager) ){
+      rc = ptrmapGet(pBt, iGuess, &eType, &pgno);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+      if( eType==PTRMAP_OVERFLOW2 && pgno==ovfl ){
+        next = iGuess;
+      }
+    }
+  }
+#endif
+
+  if( next==0 || ppPage ){
+    MemPage *pPage = 0;
+
+    rc = sqlite3BtreeGetPage(pBt, ovfl, &pPage, next!=0);
+    assert(rc==SQLITE_OK || pPage==0);
+    if( next==0 && rc==SQLITE_OK ){
+      next = get4byte(pPage->aData);
+    }
+
+    if( ppPage ){
+      *ppPage = pPage;
+    }else{
+      releasePage(pPage);
+    }
+  }
+  *pPgnoNext = next;
+
+  return rc;
+}
+
+/*
+** Copy data from a buffer to a page, or from a page to a buffer.
+**
+** pPayload is a pointer to data stored on database page pDbPage.
+** If argument eOp is false, then nByte bytes of data are copied
+** from pPayload to the buffer pointed at by pBuf. If eOp is true,
+** then sqlite3PagerWrite() is called on pDbPage and nByte bytes
+** of data are copied from the buffer pBuf to pPayload.
+**
+** SQLITE_OK is returned on success, otherwise an error code.
+*/
+static int copyPayload(
+  void *pPayload,           /* Pointer to page data */
+  void *pBuf,               /* Pointer to buffer */
+  int nByte,                /* Number of bytes to copy */
+  int eOp,                  /* 0 -> copy from page, 1 -> copy to page */
+  DbPage *pDbPage           /* Page containing pPayload */
+){
+  if( eOp ){
+    /* Copy data from buffer to page (a write operation) */
+    int rc = sqlite3PagerWrite(pDbPage);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    memcpy(pPayload, pBuf, nByte);
+  }else{
+    /* Copy data from page to buffer (a read operation) */
+    memcpy(pBuf, pPayload, nByte);
+  }
+  return SQLITE_OK;
+}
+
+/*
+** This function is used to read or overwrite payload information
+** for the entry that the pCur cursor is pointing to. If the eOp
+** parameter is 0, this is a read operation (data copied into
+** buffer pBuf). If it is non-zero, a write (data copied from
+** buffer pBuf).
+**
+** A total of "amt" bytes are read or written beginning at "offset".
+** Data is read to or from the buffer pBuf.
+**
+** This routine does not make a distinction between key and data.
+** It just reads or writes bytes from the payload area.  Data might 
+** appear on the main page or be scattered out on multiple overflow 
+** pages.
+**
+** If the BtCursor.isIncrblobHandle flag is set, and the current
+** cursor entry uses one or more overflow pages, this function
+** allocates space for and lazily popluates the overflow page-list 
+** cache array (BtCursor.aOverflow). Subsequent calls use this
+** cache to make seeking to the supplied offset more efficient.
+**
+** Once an overflow page-list cache has been allocated, it may be
+** invalidated if some other cursor writes to the same table, or if
+** the cursor is moved to a different row. Additionally, in auto-vacuum
+** mode, the following events may invalidate an overflow page-list cache.
+**
+**   * An incremental vacuum,
+**   * A commit in auto_vacuum="full" mode,
+**   * Creating a table (may require moving an overflow page).
+*/
+static int accessPayload(
+  BtCursor *pCur,      /* Cursor pointing to entry to read from */
+  int offset,          /* Begin reading this far into payload */
+  int amt,             /* Read this many bytes */
+  unsigned char *pBuf, /* Write the bytes into this buffer */ 
+  int skipKey,         /* offset begins at data if this is true */
+  int eOp              /* zero to read. non-zero to write. */
+){
+  unsigned char *aPayload;
+  int rc = SQLITE_OK;
+  u32 nKey;
+  int iIdx = 0;
+  MemPage *pPage = pCur->pPage;     /* Btree page of current cursor entry */
+  BtShared *pBt = pCur->pBt;        /* Btree this cursor belongs to */
+
+  assert( pPage );
+  assert( pCur->eState==CURSOR_VALID );
+  assert( pCur->idx>=0 && pCur->idx<pPage->nCell );
+  assert( offset>=0 );
+  assert( cursorHoldsMutex(pCur) );
+
+  getCellInfo(pCur);
+  aPayload = pCur->info.pCell + pCur->info.nHeader;
+  nKey = (pPage->intKey ? 0 : pCur->info.nKey);
+
+  if( skipKey ){
+    offset += nKey;
+  }
+  if( offset+amt > nKey+pCur->info.nData ){
+    /* Trying to read or write past the end of the data is an error */
+    return SQLITE_ERROR;
+  }
+
+  /* Check if data must be read/written to/from the btree page itself. */
+  if( offset<pCur->info.nLocal ){
+    int a = amt;
+    if( a+offset>pCur->info.nLocal ){
+      a = pCur->info.nLocal - offset;
+    }
+    rc = copyPayload(&aPayload[offset], pBuf, a, eOp, pPage->pDbPage);
+    offset = 0;
+    pBuf += a;
+    amt -= a;
+  }else{
+    offset -= pCur->info.nLocal;
+  }
+
+  if( rc==SQLITE_OK && amt>0 ){
+    const int ovflSize = pBt->usableSize - 4;  /* Bytes content per ovfl page */
+    Pgno nextPage;
+
+    nextPage = get4byte(&aPayload[pCur->info.nLocal]);
+
+#ifndef SQLITE_OMIT_INCRBLOB
+    /* If the isIncrblobHandle flag is set and the BtCursor.aOverflow[]
+    ** has not been allocated, allocate it now. The array is sized at
+    ** one entry for each overflow page in the overflow chain. The
+    ** page number of the first overflow page is stored in aOverflow[0],
+    ** etc. A value of 0 in the aOverflow[] array means "not yet known"
+    ** (the cache is lazily populated).
+    */
+    if( pCur->isIncrblobHandle && !pCur->aOverflow ){
+      int nOvfl = (pCur->info.nPayload-pCur->info.nLocal+ovflSize-1)/ovflSize;
+      pCur->aOverflow = (Pgno *)sqlite3MallocZero(sizeof(Pgno)*nOvfl);
+      if( nOvfl && !pCur->aOverflow ){
+        rc = SQLITE_NOMEM;
+      }
+    }
+
+    /* If the overflow page-list cache has been allocated and the
+    ** entry for the first required overflow page is valid, skip
+    ** directly to it.
+    */
+    if( pCur->aOverflow && pCur->aOverflow[offset/ovflSize] ){
+      iIdx = (offset/ovflSize);
+      nextPage = pCur->aOverflow[iIdx];
+      offset = (offset%ovflSize);
+    }
+#endif
+
+    for( ; rc==SQLITE_OK && amt>0 && nextPage; iIdx++){
+
+#ifndef SQLITE_OMIT_INCRBLOB
+      /* If required, populate the overflow page-list cache. */
+      if( pCur->aOverflow ){
+        assert(!pCur->aOverflow[iIdx] || pCur->aOverflow[iIdx]==nextPage);
+        pCur->aOverflow[iIdx] = nextPage;
+      }
+#endif
+
+      if( offset>=ovflSize ){
+        /* The only reason to read this page is to obtain the page
+        ** number for the next page in the overflow chain. The page
+        ** data is not required. So first try to lookup the overflow
+        ** page-list cache, if any, then fall back to the getOverflowPage()
+        ** function.
+        */
+#ifndef SQLITE_OMIT_INCRBLOB
+        if( pCur->aOverflow && pCur->aOverflow[iIdx+1] ){
+          nextPage = pCur->aOverflow[iIdx+1];
+        } else 
+#endif
+          rc = getOverflowPage(pBt, nextPage, 0, &nextPage);
+        offset -= ovflSize;
+      }else{
+        /* Need to read this page properly. It contains some of the
+        ** range of data that is being read (eOp==0) or written (eOp!=0).
+        */
+        DbPage *pDbPage;
+        int a = amt;
+        rc = sqlite3PagerGet(pBt->pPager, nextPage, &pDbPage);
+        if( rc==SQLITE_OK ){
+          aPayload = sqlite3PagerGetData(pDbPage);
+          nextPage = get4byte(aPayload);
+          if( a + offset > ovflSize ){
+            a = ovflSize - offset;
+          }
+          rc = copyPayload(&aPayload[offset+4], pBuf, a, eOp, pDbPage);
+          sqlite3PagerUnref(pDbPage);
+          offset = 0;
+          amt -= a;
+          pBuf += a;
+        }
+      }
+    }
+  }
+
+  if( rc==SQLITE_OK && amt>0 ){
+    return SQLITE_CORRUPT_BKPT;
+  }
+  return rc;
+}
+
+/*
+** Read part of the key associated with cursor pCur.  Exactly
+** "amt" bytes will be transfered into pBuf[].  The transfer
+** begins at "offset".
+**
+** Return SQLITE_OK on success or an error code if anything goes
+** wrong.  An error is returned if "offset+amt" is larger than
+** the available payload.
+*/
+int sqlite3BtreeKey(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
+  int rc;
+
+  assert( cursorHoldsMutex(pCur) );
+  rc = restoreOrClearCursorPosition(pCur);
+  if( rc==SQLITE_OK ){
+    assert( pCur->eState==CURSOR_VALID );
+    assert( pCur->pPage!=0 );
+    if( pCur->pPage->intKey ){
+      return SQLITE_CORRUPT_BKPT;
+    }
+    assert( pCur->pPage->intKey==0 );
+    assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
+    rc = accessPayload(pCur, offset, amt, (unsigned char*)pBuf, 0, 0);
+  }
+  return rc;
+}
+
+/*
+** Read part of the data associated with cursor pCur.  Exactly
+** "amt" bytes will be transfered into pBuf[].  The transfer
+** begins at "offset".
+**
+** Return SQLITE_OK on success or an error code if anything goes
+** wrong.  An error is returned if "offset+amt" is larger than
+** the available payload.
+*/
+int sqlite3BtreeData(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
+  int rc;
+
+  assert( cursorHoldsMutex(pCur) );
+  rc = restoreOrClearCursorPosition(pCur);
+  if( rc==SQLITE_OK ){
+    assert( pCur->eState==CURSOR_VALID );
+    assert( pCur->pPage!=0 );
+    assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
+    rc = accessPayload(pCur, offset, amt, pBuf, 1, 0);
+  }
+  return rc;
+}
+
+/*
+** Return a pointer to payload information from the entry that the 
+** pCur cursor is pointing to.  The pointer is to the beginning of
+** the key if skipKey==0 and it points to the beginning of data if
+** skipKey==1.  The number of bytes of available key/data is written
+** into *pAmt.  If *pAmt==0, then the value returned will not be
+** a valid pointer.
+**
+** This routine is an optimization.  It is common for the entire key
+** and data to fit on the local page and for there to be no overflow
+** pages.  When that is so, this routine can be used to access the
+** key and data without making a copy.  If the key and/or data spills
+** onto overflow pages, then accessPayload() must be used to reassembly
+** the key/data and copy it into a preallocated buffer.
+**
+** The pointer returned by this routine looks directly into the cached
+** page of the database.  The data might change or move the next time
+** any btree routine is called.
+*/
+static const unsigned char *fetchPayload(
+  BtCursor *pCur,      /* Cursor pointing to entry to read from */
+  int *pAmt,           /* Write the number of available bytes here */
+  int skipKey          /* read beginning at data if this is true */
+){
+  unsigned char *aPayload;
+  MemPage *pPage;
+  u32 nKey;
+  int nLocal;
+
+  assert( pCur!=0 && pCur->pPage!=0 );
+  assert( pCur->eState==CURSOR_VALID );
+  assert( cursorHoldsMutex(pCur) );
+  pPage = pCur->pPage;
+  assert( pCur->idx>=0 && pCur->idx<pPage->nCell );
+  getCellInfo(pCur);
+  aPayload = pCur->info.pCell;
+  aPayload += pCur->info.nHeader;
+  if( pPage->intKey ){
+    nKey = 0;
+  }else{
+    nKey = pCur->info.nKey;
+  }
+  if( skipKey ){
+    aPayload += nKey;
+    nLocal = pCur->info.nLocal - nKey;
+  }else{
+    nLocal = pCur->info.nLocal;
+    if( nLocal>nKey ){
+      nLocal = nKey;
+    }
+  }
+  *pAmt = nLocal;
+  return aPayload;
+}
+
+
+/*
+** For the entry that cursor pCur is point to, return as
+** many bytes of the key or data as are available on the local
+** b-tree page.  Write the number of available bytes into *pAmt.
+**
+** The pointer returned is ephemeral.  The key/data may move
+** or be destroyed on the next call to any Btree routine,
+** including calls from other threads against the same cache.
+** Hence, a mutex on the BtShared should be held prior to calling
+** this routine.
+**
+** These routines is used to get quick access to key and data
+** in the common case where no overflow pages are used.
+*/
+const void *sqlite3BtreeKeyFetch(BtCursor *pCur, int *pAmt){
+  assert( cursorHoldsMutex(pCur) );
+  if( pCur->eState==CURSOR_VALID ){
+    return (const void*)fetchPayload(pCur, pAmt, 0);
+  }
+  return 0;
+}
+const void *sqlite3BtreeDataFetch(BtCursor *pCur, int *pAmt){
+  assert( cursorHoldsMutex(pCur) );
+  if( pCur->eState==CURSOR_VALID ){
+    return (const void*)fetchPayload(pCur, pAmt, 1);
+  }
+  return 0;
+}
+
+
+/*
+** Move the cursor down to a new child page.  The newPgno argument is the
+** page number of the child page to move to.
+*/
+static int moveToChild(BtCursor *pCur, u32 newPgno){
+  int rc;
+  MemPage *pNewPage;
+  MemPage *pOldPage;
+  BtShared *pBt = pCur->pBt;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( pCur->eState==CURSOR_VALID );
+  rc = getAndInitPage(pBt, newPgno, &pNewPage, pCur->pPage);
+  if( rc ) return rc;
+  pNewPage->idxParent = pCur->idx;
+  pOldPage = pCur->pPage;
+  pOldPage->idxShift = 0;
+  releasePage(pOldPage);
+  pCur->pPage = pNewPage;
+  pCur->idx = 0;
+  pCur->info.nSize = 0;
+  if( pNewPage->nCell<1 ){
+    return SQLITE_CORRUPT_BKPT;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Return true if the page is the virtual root of its table.
+**
+** The virtual root page is the root page for most tables.  But
+** for the table rooted on page 1, sometime the real root page
+** is empty except for the right-pointer.  In such cases the
+** virtual root page is the page that the right-pointer of page
+** 1 is pointing to.
+*/
+int sqlite3BtreeIsRootPage(MemPage *pPage){
+  MemPage *pParent;
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  pParent = pPage->pParent;
+  if( pParent==0 ) return 1;
+  if( pParent->pgno>1 ) return 0;
+  if( get2byte(&pParent->aData[pParent->hdrOffset+3])==0 ) return 1;
+  return 0;
+}
+
+/*
+** Move the cursor up to the parent page.
+**
+** pCur->idx is set to the cell index that contains the pointer
+** to the page we are coming from.  If we are coming from the
+** right-most child page then pCur->idx is set to one more than
+** the largest cell index.
+*/
+void sqlite3BtreeMoveToParent(BtCursor *pCur){
+  MemPage *pParent;
+  MemPage *pPage;
+  int idxParent;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( pCur->eState==CURSOR_VALID );
+  pPage = pCur->pPage;
+  assert( pPage!=0 );
+  assert( !sqlite3BtreeIsRootPage(pPage) );
+  pParent = pPage->pParent;
+  assert( pParent!=0 );
+  idxParent = pPage->idxParent;
+  sqlite3PagerRef(pParent->pDbPage);
+  releasePage(pPage);
+  pCur->pPage = pParent;
+  pCur->info.nSize = 0;
+  assert( pParent->idxShift==0 );
+  pCur->idx = idxParent;
+}
+
+/*
+** Move the cursor to the root page
+*/
+static int moveToRoot(BtCursor *pCur){
+  MemPage *pRoot;
+  int rc = SQLITE_OK;
+  Btree *p = pCur->pBtree;
+  BtShared *pBt = p->pBt;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
+  assert( CURSOR_VALID   < CURSOR_REQUIRESEEK );
+  assert( CURSOR_FAULT   > CURSOR_REQUIRESEEK );
+  if( pCur->eState>=CURSOR_REQUIRESEEK ){
+    if( pCur->eState==CURSOR_FAULT ){
+      return pCur->skip;
+    }
+    clearCursorPosition(pCur);
+  }
+  pRoot = pCur->pPage;
+  if( pRoot && pRoot->pgno==pCur->pgnoRoot ){
+    assert( pRoot->isInit );
+  }else{
+    if( 
+      SQLITE_OK!=(rc = getAndInitPage(pBt, pCur->pgnoRoot, &pRoot, 0))
+    ){
+      pCur->eState = CURSOR_INVALID;
+      return rc;
+    }
+    releasePage(pCur->pPage);
+    pCur->pPage = pRoot;
+  }
+  pCur->idx = 0;
+  pCur->info.nSize = 0;
+  if( pRoot->nCell==0 && !pRoot->leaf ){
+    Pgno subpage;
+    assert( pRoot->pgno==1 );
+    subpage = get4byte(&pRoot->aData[pRoot->hdrOffset+8]);
+    assert( subpage>0 );
+    pCur->eState = CURSOR_VALID;
+    rc = moveToChild(pCur, subpage);
+  }
+  pCur->eState = ((pCur->pPage->nCell>0)?CURSOR_VALID:CURSOR_INVALID);
+  return rc;
+}
+
+/*
+** Move the cursor down to the left-most leaf entry beneath the
+** entry to which it is currently pointing.
+**
+** The left-most leaf is the one with the smallest key - the first
+** in ascending order.
+*/
+static int moveToLeftmost(BtCursor *pCur){
+  Pgno pgno;
+  int rc = SQLITE_OK;
+  MemPage *pPage;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( pCur->eState==CURSOR_VALID );
+  while( rc==SQLITE_OK && !(pPage = pCur->pPage)->leaf ){
+    assert( pCur->idx>=0 && pCur->idx<pPage->nCell );
+    pgno = get4byte(findCell(pPage, pCur->idx));
+    rc = moveToChild(pCur, pgno);
+  }
+  return rc;
+}
+
+/*
+** Move the cursor down to the right-most leaf entry beneath the
+** page to which it is currently pointing.  Notice the difference
+** between moveToLeftmost() and moveToRightmost().  moveToLeftmost()
+** finds the left-most entry beneath the *entry* whereas moveToRightmost()
+** finds the right-most entry beneath the *page*.
+**
+** The right-most entry is the one with the largest key - the last
+** key in ascending order.
+*/
+static int moveToRightmost(BtCursor *pCur){
+  Pgno pgno;
+  int rc = SQLITE_OK;
+  MemPage *pPage;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( pCur->eState==CURSOR_VALID );
+  while( rc==SQLITE_OK && !(pPage = pCur->pPage)->leaf ){
+    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
+    pCur->idx = pPage->nCell;
+    rc = moveToChild(pCur, pgno);
+  }
+  if( rc==SQLITE_OK ){
+    pCur->idx = pPage->nCell - 1;
+    pCur->info.nSize = 0;
+  }
+  return SQLITE_OK;
+}
+
+/* Move the cursor to the first entry in the table.  Return SQLITE_OK
+** on success.  Set *pRes to 0 if the cursor actually points to something
+** or set *pRes to 1 if the table is empty.
+*/
+int sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
+  int rc;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( sqlite3_mutex_held(pCur->pBtree->pSqlite->mutex) );
+  rc = moveToRoot(pCur);
+  if( rc==SQLITE_OK ){
+    if( pCur->eState==CURSOR_INVALID ){
+      assert( pCur->pPage->nCell==0 );
+      *pRes = 1;
+      rc = SQLITE_OK;
+    }else{
+      assert( pCur->pPage->nCell>0 );
+      *pRes = 0;
+      rc = moveToLeftmost(pCur);
+    }
+  }
+  return rc;
+}
+
+/* Move the cursor to the last entry in the table.  Return SQLITE_OK
+** on success.  Set *pRes to 0 if the cursor actually points to something
+** or set *pRes to 1 if the table is empty.
+*/
+int sqlite3BtreeLast(BtCursor *pCur, int *pRes){
+  int rc;
+ 
+  assert( cursorHoldsMutex(pCur) );
+  assert( sqlite3_mutex_held(pCur->pBtree->pSqlite->mutex) );
+  rc = moveToRoot(pCur);
+  if( rc==SQLITE_OK ){
+    if( CURSOR_INVALID==pCur->eState ){
+      assert( pCur->pPage->nCell==0 );
+      *pRes = 1;
+    }else{
+      assert( pCur->eState==CURSOR_VALID );
+      *pRes = 0;
+      rc = moveToRightmost(pCur);
+    }
+  }
+  return rc;
+}
+
+/* Move the cursor so that it points to an entry near pKey/nKey.
+** Return a success code.
+**
+** For INTKEY tables, only the nKey parameter is used.  pKey is
+** ignored.  For other tables, nKey is the number of bytes of data
+** in pKey.  The comparison function specified when the cursor was
+** created is used to compare keys.
+**
+** If an exact match is not found, then the cursor is always
+** left pointing at a leaf page which would hold the entry if it
+** were present.  The cursor might point to an entry that comes
+** before or after the key.
+**
+** The result of comparing the key with the entry to which the
+** cursor is written to *pRes if pRes!=NULL.  The meaning of
+** this value is as follows:
+**
+**     *pRes<0      The cursor is left pointing at an entry that
+**                  is smaller than pKey or if the table is empty
+**                  and the cursor is therefore left point to nothing.
+**
+**     *pRes==0     The cursor is left pointing at an entry that
+**                  exactly matches pKey.
+**
+**     *pRes>0      The cursor is left pointing at an entry that
+**                  is larger than pKey.
+**
+*/
+int sqlite3BtreeMoveto(
+  BtCursor *pCur,        /* The cursor to be moved */
+  const void *pKey,      /* The key content for indices.  Not used by tables */
+  i64 nKey,              /* Size of pKey.  Or the key for tables */
+  int biasRight,         /* If true, bias the search to the high end */
+  int *pRes              /* Search result flag */
+){
+  int rc;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( sqlite3_mutex_held(pCur->pBtree->pSqlite->mutex) );
+  rc = moveToRoot(pCur);
+  if( rc ){
+    return rc;
+  }
+  assert( pCur->pPage );
+  assert( pCur->pPage->isInit );
+  if( pCur->eState==CURSOR_INVALID ){
+    *pRes = -1;
+    assert( pCur->pPage->nCell==0 );
+    return SQLITE_OK;
+  }
+  for(;;){
+    int lwr, upr;
+    Pgno chldPg;
+    MemPage *pPage = pCur->pPage;
+    int c = -1;  /* pRes return if table is empty must be -1 */
+    lwr = 0;
+    upr = pPage->nCell-1;
+    if( !pPage->intKey && pKey==0 ){
+      return SQLITE_CORRUPT_BKPT;
+    }
+    if( biasRight ){
+      pCur->idx = upr;
+    }else{
+      pCur->idx = (upr+lwr)/2;
+    }
+    if( lwr<=upr ) for(;;){
+      void *pCellKey;
+      i64 nCellKey;
+      pCur->info.nSize = 0;
+      if( pPage->intKey ){
+        u8 *pCell;
+        pCell = findCell(pPage, pCur->idx) + pPage->childPtrSize;
+        if( pPage->hasData ){
+          u32 dummy;
+          pCell += getVarint32(pCell, &dummy);
+        }
+        getVarint(pCell, (u64 *)&nCellKey);
+        if( nCellKey<nKey ){
+          c = -1;
+        }else if( nCellKey>nKey ){
+          c = +1;
+        }else{
+          c = 0;
+        }
+      }else{
+        int available;
+        pCellKey = (void *)fetchPayload(pCur, &available, 0);
+        nCellKey = pCur->info.nKey;
+        if( available>=nCellKey ){
+          c = pCur->xCompare(pCur->pArg, nCellKey, pCellKey, nKey, pKey);
+        }else{
+          pCellKey = sqlite3_malloc( nCellKey );
+          if( pCellKey==0 ) return SQLITE_NOMEM;
+          rc = sqlite3BtreeKey(pCur, 0, nCellKey, (void *)pCellKey);
+          c = pCur->xCompare(pCur->pArg, nCellKey, pCellKey, nKey, pKey);
+          sqlite3_free(pCellKey);
+          if( rc ){
+            return rc;
+          }
+        }
+      }
+      if( c==0 ){
+        if( pPage->leafData && !pPage->leaf ){
+          lwr = pCur->idx;
+          upr = lwr - 1;
+          break;
+        }else{
+          if( pRes ) *pRes = 0;
+          return SQLITE_OK;
+        }
+      }
+      if( c<0 ){
+        lwr = pCur->idx+1;
+      }else{
+        upr = pCur->idx-1;
+      }
+      if( lwr>upr ){
+        break;
+      }
+      pCur->idx = (lwr+upr)/2;
+    }
+    assert( lwr==upr+1 );
+    assert( pPage->isInit );
+    if( pPage->leaf ){
+      chldPg = 0;
+    }else if( lwr>=pPage->nCell ){
+      chldPg = get4byte(&pPage->aData[pPage->hdrOffset+8]);
+    }else{
+      chldPg = get4byte(findCell(pPage, lwr));
+    }
+    if( chldPg==0 ){
+      assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
+      if( pRes ) *pRes = c;
+      return SQLITE_OK;
+    }
+    pCur->idx = lwr;
+    pCur->info.nSize = 0;
+    rc = moveToChild(pCur, chldPg);
+    if( rc ){
+      return rc;
+    }
+  }
+  /* NOT REACHED */
+}
+
+
+/*
+** Return TRUE if the cursor is not pointing at an entry of the table.
+**
+** TRUE will be returned after a call to sqlite3BtreeNext() moves
+** past the last entry in the table or sqlite3BtreePrev() moves past
+** the first entry.  TRUE is also returned if the table is empty.
+*/
+int sqlite3BtreeEof(BtCursor *pCur){
+  /* TODO: What if the cursor is in CURSOR_REQUIRESEEK but all table entries
+  ** have been deleted? This API will need to change to return an error code
+  ** as well as the boolean result value.
+  */
+  return (CURSOR_VALID!=pCur->eState);
+}
+
+/*
+** Return the database connection handle for a cursor.
+*/
+sqlite3 *sqlite3BtreeCursorDb(const BtCursor *pCur){
+  assert( sqlite3_mutex_held(pCur->pBtree->pSqlite->mutex) );
+  return pCur->pBtree->pSqlite;
+}
+
+/*
+** Advance the cursor to the next entry in the database.  If
+** successful then set *pRes=0.  If the cursor
+** was already pointing to the last entry in the database before
+** this routine was called, then set *pRes=1.
+*/
+static int btreeNext(BtCursor *pCur, int *pRes){
+  int rc;
+  MemPage *pPage;
+
+  assert( cursorHoldsMutex(pCur) );
+  rc = restoreOrClearCursorPosition(pCur);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  assert( pRes!=0 );
+  pPage = pCur->pPage;
+  if( CURSOR_INVALID==pCur->eState ){
+    *pRes = 1;
+    return SQLITE_OK;
+  }
+  if( pCur->skip>0 ){
+    pCur->skip = 0;
+    *pRes = 0;
+    return SQLITE_OK;
+  }
+  pCur->skip = 0;
+
+  assert( pPage->isInit );
+  assert( pCur->idx<pPage->nCell );
+
+  pCur->idx++;
+  pCur->info.nSize = 0;
+  if( pCur->idx>=pPage->nCell ){
+    if( !pPage->leaf ){
+      rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+8]));
+      if( rc ) return rc;
+      rc = moveToLeftmost(pCur);
+      *pRes = 0;
+      return rc;
+    }
+    do{
+      if( sqlite3BtreeIsRootPage(pPage) ){
+        *pRes = 1;
+        pCur->eState = CURSOR_INVALID;
+        return SQLITE_OK;
+      }
+      sqlite3BtreeMoveToParent(pCur);
+      pPage = pCur->pPage;
+    }while( pCur->idx>=pPage->nCell );
+    *pRes = 0;
+    if( pPage->leafData ){
+      rc = sqlite3BtreeNext(pCur, pRes);
+    }else{
+      rc = SQLITE_OK;
+    }
+    return rc;
+  }
+  *pRes = 0;
+  if( pPage->leaf ){
+    return SQLITE_OK;
+  }
+  rc = moveToLeftmost(pCur);
+  return rc;
+}
+int sqlite3BtreeNext(BtCursor *pCur, int *pRes){
+  int rc;
+  assert( cursorHoldsMutex(pCur) );
+  rc = btreeNext(pCur, pRes);
+  return rc;
+}
+
+
+/*
+** Step the cursor to the back to the previous entry in the database.  If
+** successful then set *pRes=0.  If the cursor
+** was already pointing to the first entry in the database before
+** this routine was called, then set *pRes=1.
+*/
+static int btreePrevious(BtCursor *pCur, int *pRes){
+  int rc;
+  Pgno pgno;
+  MemPage *pPage;
+
+  assert( cursorHoldsMutex(pCur) );
+  rc = restoreOrClearCursorPosition(pCur);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  if( CURSOR_INVALID==pCur->eState ){
+    *pRes = 1;
+    return SQLITE_OK;
+  }
+  if( pCur->skip<0 ){
+    pCur->skip = 0;
+    *pRes = 0;
+    return SQLITE_OK;
+  }
+  pCur->skip = 0;
+
+  pPage = pCur->pPage;
+  assert( pPage->isInit );
+  assert( pCur->idx>=0 );
+  if( !pPage->leaf ){
+    pgno = get4byte( findCell(pPage, pCur->idx) );
+    rc = moveToChild(pCur, pgno);
+    if( rc ){
+      return rc;
+    }
+    rc = moveToRightmost(pCur);
+  }else{
+    while( pCur->idx==0 ){
+      if( sqlite3BtreeIsRootPage(pPage) ){
+        pCur->eState = CURSOR_INVALID;
+        *pRes = 1;
+        return SQLITE_OK;
+      }
+      sqlite3BtreeMoveToParent(pCur);
+      pPage = pCur->pPage;
+    }
+    pCur->idx--;
+    pCur->info.nSize = 0;
+    if( pPage->leafData && !pPage->leaf ){
+      rc = sqlite3BtreePrevious(pCur, pRes);
+    }else{
+      rc = SQLITE_OK;
+    }
+  }
+  *pRes = 0;
+  return rc;
+}
+int sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
+  int rc;
+  assert( cursorHoldsMutex(pCur) );
+  rc = btreePrevious(pCur, pRes);
+  return rc;
+}
+
+/*
+** Allocate a new page from the database file.
+**
+** The new page is marked as dirty.  (In other words, sqlite3PagerWrite()
+** has already been called on the new page.)  The new page has also
+** been referenced and the calling routine is responsible for calling
+** sqlite3PagerUnref() on the new page when it is done.
+**
+** SQLITE_OK is returned on success.  Any other return value indicates
+** an error.  *ppPage and *pPgno are undefined in the event of an error.
+** Do not invoke sqlite3PagerUnref() on *ppPage if an error is returned.
+**
+** If the "nearby" parameter is not 0, then a (feeble) effort is made to 
+** locate a page close to the page number "nearby".  This can be used in an
+** attempt to keep related pages close to each other in the database file,
+** which in turn can make database access faster.
+**
+** If the "exact" parameter is not 0, and the page-number nearby exists 
+** anywhere on the free-list, then it is guarenteed to be returned. This
+** is only used by auto-vacuum databases when allocating a new table.
+*/
+static int allocateBtreePage(
+  BtShared *pBt, 
+  MemPage **ppPage, 
+  Pgno *pPgno, 
+  Pgno nearby,
+  u8 exact
+){
+  MemPage *pPage1;
+  int rc;
+  int n;     /* Number of pages on the freelist */
+  int k;     /* Number of leaves on the trunk of the freelist */
+  MemPage *pTrunk = 0;
+  MemPage *pPrevTrunk = 0;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  pPage1 = pBt->pPage1;
+  n = get4byte(&pPage1->aData[36]);
+  if( n>0 ){
+    /* There are pages on the freelist.  Reuse one of those pages. */
+    Pgno iTrunk;
+    u8 searchList = 0; /* If the free-list must be searched for 'nearby' */
+    
+    /* If the 'exact' parameter was true and a query of the pointer-map
+    ** shows that the page 'nearby' is somewhere on the free-list, then
+    ** the entire-list will be searched for that page.
+    */
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( exact && nearby<=sqlite3PagerPagecount(pBt->pPager) ){
+      u8 eType;
+      assert( nearby>0 );
+      assert( pBt->autoVacuum );
+      rc = ptrmapGet(pBt, nearby, &eType, 0);
+      if( rc ) return rc;
+      if( eType==PTRMAP_FREEPAGE ){
+        searchList = 1;
+      }
+      *pPgno = nearby;
+    }
+#endif
+
+    /* Decrement the free-list count by 1. Set iTrunk to the index of the
+    ** first free-list trunk page. iPrevTrunk is initially 1.
+    */
+    rc = sqlite3PagerWrite(pPage1->pDbPage);
+    if( rc ) return rc;
+    put4byte(&pPage1->aData[36], n-1);
+
+    /* The code within this loop is run only once if the 'searchList' variable
+    ** is not true. Otherwise, it runs once for each trunk-page on the
+    ** free-list until the page 'nearby' is located.
+    */
+    do {
+      pPrevTrunk = pTrunk;
+      if( pPrevTrunk ){
+        iTrunk = get4byte(&pPrevTrunk->aData[0]);
+      }else{
+        iTrunk = get4byte(&pPage1->aData[32]);
+      }
+      rc = sqlite3BtreeGetPage(pBt, iTrunk, &pTrunk, 0);
+      if( rc ){
+        pTrunk = 0;
+        goto end_allocate_page;
+      }
+
+      k = get4byte(&pTrunk->aData[4]);
+      if( k==0 && !searchList ){
+        /* The trunk has no leaves and the list is not being searched. 
+        ** So extract the trunk page itself and use it as the newly 
+        ** allocated page */
+        assert( pPrevTrunk==0 );
+        rc = sqlite3PagerWrite(pTrunk->pDbPage);
+        if( rc ){
+          goto end_allocate_page;
+        }
+        *pPgno = iTrunk;
+        memcpy(&pPage1->aData[32], &pTrunk->aData[0], 4);
+        *ppPage = pTrunk;
+        pTrunk = 0;
+        TRACE(("ALLOCATE: %d trunk - %d free pages left\n", *pPgno, n-1));
+      }else if( k>pBt->usableSize/4 - 8 ){
+        /* Value of k is out of range.  Database corruption */
+        rc = SQLITE_CORRUPT_BKPT;
+        goto end_allocate_page;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      }else if( searchList && nearby==iTrunk ){
+        /* The list is being searched and this trunk page is the page
+        ** to allocate, regardless of whether it has leaves.
+        */
+        assert( *pPgno==iTrunk );
+        *ppPage = pTrunk;
+        searchList = 0;
+        rc = sqlite3PagerWrite(pTrunk->pDbPage);
+        if( rc ){
+          goto end_allocate_page;
+        }
+        if( k==0 ){
+          if( !pPrevTrunk ){
+            memcpy(&pPage1->aData[32], &pTrunk->aData[0], 4);
+          }else{
+            memcpy(&pPrevTrunk->aData[0], &pTrunk->aData[0], 4);
+          }
+        }else{
+          /* The trunk page is required by the caller but it contains 
+          ** pointers to free-list leaves. The first leaf becomes a trunk
+          ** page in this case.
+          */
+          MemPage *pNewTrunk;
+          Pgno iNewTrunk = get4byte(&pTrunk->aData[8]);
+          rc = sqlite3BtreeGetPage(pBt, iNewTrunk, &pNewTrunk, 0);
+          if( rc!=SQLITE_OK ){
+            goto end_allocate_page;
+          }
+          rc = sqlite3PagerWrite(pNewTrunk->pDbPage);
+          if( rc!=SQLITE_OK ){
+            releasePage(pNewTrunk);
+            goto end_allocate_page;
+          }
+          memcpy(&pNewTrunk->aData[0], &pTrunk->aData[0], 4);
+          put4byte(&pNewTrunk->aData[4], k-1);
+          memcpy(&pNewTrunk->aData[8], &pTrunk->aData[12], (k-1)*4);
+          releasePage(pNewTrunk);
+          if( !pPrevTrunk ){
+            put4byte(&pPage1->aData[32], iNewTrunk);
+          }else{
+            rc = sqlite3PagerWrite(pPrevTrunk->pDbPage);
+            if( rc ){
+              goto end_allocate_page;
+            }
+            put4byte(&pPrevTrunk->aData[0], iNewTrunk);
+          }
+        }
+        pTrunk = 0;
+        TRACE(("ALLOCATE: %d trunk - %d free pages left\n", *pPgno, n-1));
+#endif
+      }else{
+        /* Extract a leaf from the trunk */
+        int closest;
+        Pgno iPage;
+        unsigned char *aData = pTrunk->aData;
+        rc = sqlite3PagerWrite(pTrunk->pDbPage);
+        if( rc ){
+          goto end_allocate_page;
+        }
+        if( nearby>0 ){
+          int i, dist;
+          closest = 0;
+          dist = get4byte(&aData[8]) - nearby;
+          if( dist<0 ) dist = -dist;
+          for(i=1; i<k; i++){
+            int d2 = get4byte(&aData[8+i*4]) - nearby;
+            if( d2<0 ) d2 = -d2;
+            if( d2<dist ){
+              closest = i;
+              dist = d2;
+            }
+          }
+        }else{
+          closest = 0;
+        }
+
+        iPage = get4byte(&aData[8+closest*4]);
+        if( !searchList || iPage==nearby ){
+          *pPgno = iPage;
+          if( *pPgno>sqlite3PagerPagecount(pBt->pPager) ){
+            /* Free page off the end of the file */
+            return SQLITE_CORRUPT_BKPT;
+          }
+          TRACE(("ALLOCATE: %d was leaf %d of %d on trunk %d"
+                 ": %d more free pages\n",
+                 *pPgno, closest+1, k, pTrunk->pgno, n-1));
+          if( closest<k-1 ){
+            memcpy(&aData[8+closest*4], &aData[4+k*4], 4);
+          }
+          put4byte(&aData[4], k-1);
+          rc = sqlite3BtreeGetPage(pBt, *pPgno, ppPage, 1);
+          if( rc==SQLITE_OK ){
+            sqlite3PagerDontRollback((*ppPage)->pDbPage);
+            rc = sqlite3PagerWrite((*ppPage)->pDbPage);
+            if( rc!=SQLITE_OK ){
+              releasePage(*ppPage);
+            }
+          }
+          searchList = 0;
+        }
+      }
+      releasePage(pPrevTrunk);
+      pPrevTrunk = 0;
+    }while( searchList );
+  }else{
+    /* There are no pages on the freelist, so create a new page at the
+    ** end of the file */
+    *pPgno = sqlite3PagerPagecount(pBt->pPager) + 1;
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( pBt->nTrunc ){
+      /* An incr-vacuum has already run within this transaction. So the
+      ** page to allocate is not from the physical end of the file, but
+      ** at pBt->nTrunc. 
+      */
+      *pPgno = pBt->nTrunc+1;
+      if( *pPgno==PENDING_BYTE_PAGE(pBt) ){
+        (*pPgno)++;
+      }
+    }
+    if( pBt->autoVacuum && PTRMAP_ISPAGE(pBt, *pPgno) ){
+      /* If *pPgno refers to a pointer-map page, allocate two new pages
+      ** at the end of the file instead of one. The first allocated page
+      ** becomes a new pointer-map page, the second is used by the caller.
+      */
+      TRACE(("ALLOCATE: %d from end of file (pointer-map page)\n", *pPgno));
+      assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
+      (*pPgno)++;
+    }
+    if( pBt->nTrunc ){
+      pBt->nTrunc = *pPgno;
+    }
+#endif
+
+    assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
+    rc = sqlite3BtreeGetPage(pBt, *pPgno, ppPage, 0);
+    if( rc ) return rc;
+    rc = sqlite3PagerWrite((*ppPage)->pDbPage);
+    if( rc!=SQLITE_OK ){
+      releasePage(*ppPage);
+    }
+    TRACE(("ALLOCATE: %d from end of file\n", *pPgno));
+  }
+
+  assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
+
+end_allocate_page:
+  releasePage(pTrunk);
+  releasePage(pPrevTrunk);
+  return rc;
+}
+
+/*
+** Add a page of the database file to the freelist.
+**
+** sqlite3PagerUnref() is NOT called for pPage.
+*/
+static int freePage(MemPage *pPage){
+  BtShared *pBt = pPage->pBt;
+  MemPage *pPage1 = pBt->pPage1;
+  int rc, n, k;
+
+  /* Prepare the page for freeing */
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  assert( pPage->pgno>1 );
+  pPage->isInit = 0;
+  releasePage(pPage->pParent);
+  pPage->pParent = 0;
+
+  /* Increment the free page count on pPage1 */
+  rc = sqlite3PagerWrite(pPage1->pDbPage);
+  if( rc ) return rc;
+  n = get4byte(&pPage1->aData[36]);
+  put4byte(&pPage1->aData[36], n+1);
+
+#ifdef SQLITE_SECURE_DELETE
+  /* If the SQLITE_SECURE_DELETE compile-time option is enabled, then
+  ** always fully overwrite deleted information with zeros.
+  */
+  rc = sqlite3PagerWrite(pPage->pDbPage);
+  if( rc ) return rc;
+  memset(pPage->aData, 0, pPage->pBt->pageSize);
+#endif
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  /* If the database supports auto-vacuum, write an entry in the pointer-map
+  ** to indicate that the page is free.
+  */
+  if( pBt->autoVacuum ){
+    rc = ptrmapPut(pBt, pPage->pgno, PTRMAP_FREEPAGE, 0);
+    if( rc ) return rc;
+  }
+#endif
+
+  if( n==0 ){
+    /* This is the first free page */
+    rc = sqlite3PagerWrite(pPage->pDbPage);
+    if( rc ) return rc;
+    memset(pPage->aData, 0, 8);
+    put4byte(&pPage1->aData[32], pPage->pgno);
+    TRACE(("FREE-PAGE: %d first\n", pPage->pgno));
+  }else{
+    /* Other free pages already exist.  Retrive the first trunk page
+    ** of the freelist and find out how many leaves it has. */
+    MemPage *pTrunk;
+    rc = sqlite3BtreeGetPage(pBt, get4byte(&pPage1->aData[32]), &pTrunk, 0);
+    if( rc ) return rc;
+    k = get4byte(&pTrunk->aData[4]);
+    if( k>=pBt->usableSize/4 - 8 ){
+      /* The trunk is full.  Turn the page being freed into a new
+      ** trunk page with no leaves. */
+      rc = sqlite3PagerWrite(pPage->pDbPage);
+      if( rc==SQLITE_OK ){
+        put4byte(pPage->aData, pTrunk->pgno);
+        put4byte(&pPage->aData[4], 0);
+        put4byte(&pPage1->aData[32], pPage->pgno);
+        TRACE(("FREE-PAGE: %d new trunk page replacing %d\n",
+                pPage->pgno, pTrunk->pgno));
+      }
+    }else if( k<0 ){
+      rc = SQLITE_CORRUPT;
+    }else{
+      /* Add the newly freed page as a leaf on the current trunk */
+      rc = sqlite3PagerWrite(pTrunk->pDbPage);
+      if( rc==SQLITE_OK ){
+        put4byte(&pTrunk->aData[4], k+1);
+        put4byte(&pTrunk->aData[8+k*4], pPage->pgno);
+#ifndef SQLITE_SECURE_DELETE
+        sqlite3PagerDontWrite(pPage->pDbPage);
+#endif
+      }
+      TRACE(("FREE-PAGE: %d leaf on trunk page %d\n",pPage->pgno,pTrunk->pgno));
+    }
+    releasePage(pTrunk);
+  }
+  return rc;
+}
+
+/*
+** Free any overflow pages associated with the given Cell.
+*/
+static int clearCell(MemPage *pPage, unsigned char *pCell){
+  BtShared *pBt = pPage->pBt;
+  CellInfo info;
+  Pgno ovflPgno;
+  int rc;
+  int nOvfl;
+  int ovflPageSize;
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+  if( info.iOverflow==0 ){
+    return SQLITE_OK;  /* No overflow pages. Return without doing anything */
+  }
+  ovflPgno = get4byte(&pCell[info.iOverflow]);
+  ovflPageSize = pBt->usableSize - 4;
+  nOvfl = (info.nPayload - info.nLocal + ovflPageSize - 1)/ovflPageSize;
+  assert( ovflPgno==0 || nOvfl>0 );
+  while( nOvfl-- ){
+    MemPage *pOvfl;
+    if( ovflPgno==0 || ovflPgno>sqlite3PagerPagecount(pBt->pPager) ){
+      return SQLITE_CORRUPT_BKPT;
+    }
+
+    rc = getOverflowPage(pBt, ovflPgno, &pOvfl, (nOvfl==0)?0:&ovflPgno);
+    if( rc ) return rc;
+    rc = freePage(pOvfl);
+    sqlite3PagerUnref(pOvfl->pDbPage);
+    if( rc ) return rc;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Create the byte sequence used to represent a cell on page pPage
+** and write that byte sequence into pCell[].  Overflow pages are
+** allocated and filled in as necessary.  The calling procedure
+** is responsible for making sure sufficient space has been allocated
+** for pCell[].
+**
+** Note that pCell does not necessary need to point to the pPage->aData
+** area.  pCell might point to some temporary storage.  The cell will
+** be constructed in this temporary area then copied into pPage->aData
+** later.
+*/
+static int fillInCell(
+  MemPage *pPage,                /* The page that contains the cell */
+  unsigned char *pCell,          /* Complete text of the cell */
+  const void *pKey, i64 nKey,    /* The key */
+  const void *pData,int nData,   /* The data */
+  int nZero,                     /* Extra zero bytes to append to pData */
+  int *pnSize                    /* Write cell size here */
+){
+  int nPayload;
+  const u8 *pSrc;
+  int nSrc, n, rc;
+  int spaceLeft;
+  MemPage *pOvfl = 0;
+  MemPage *pToRelease = 0;
+  unsigned char *pPrior;
+  unsigned char *pPayload;
+  BtShared *pBt = pPage->pBt;
+  Pgno pgnoOvfl = 0;
+  int nHeader;
+  CellInfo info;
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+
+  /* Fill in the header. */
+  nHeader = 0;
+  if( !pPage->leaf ){
+    nHeader += 4;
+  }
+  if( pPage->hasData ){
+    nHeader += putVarint(&pCell[nHeader], nData+nZero);
+  }else{
+    nData = nZero = 0;
+  }
+  nHeader += putVarint(&pCell[nHeader], *(u64*)&nKey);
+  sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+  assert( info.nHeader==nHeader );
+  assert( info.nKey==nKey );
+  assert( info.nData==nData+nZero );
+  
+  /* Fill in the payload */
+  nPayload = nData + nZero;
+  if( pPage->intKey ){
+    pSrc = pData;
+    nSrc = nData;
+    nData = 0;
+  }else{
+    nPayload += nKey;
+    pSrc = pKey;
+    nSrc = nKey;
+  }
+  *pnSize = info.nSize;
+  spaceLeft = info.nLocal;
+  pPayload = &pCell[nHeader];
+  pPrior = &pCell[info.iOverflow];
+
+  while( nPayload>0 ){
+    if( spaceLeft==0 ){
+      int isExact = 0;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      Pgno pgnoPtrmap = pgnoOvfl; /* Overflow page pointer-map entry page */
+      if( pBt->autoVacuum ){
+        do{
+          pgnoOvfl++;
+        } while( 
+          PTRMAP_ISPAGE(pBt, pgnoOvfl) || pgnoOvfl==PENDING_BYTE_PAGE(pBt) 
+        );
+        if( pgnoOvfl>1 ){
+          /* isExact = 1; */
+        }
+      }
+#endif
+      rc = allocateBtreePage(pBt, &pOvfl, &pgnoOvfl, pgnoOvfl, isExact);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      /* If the database supports auto-vacuum, and the second or subsequent
+      ** overflow page is being allocated, add an entry to the pointer-map
+      ** for that page now. 
+      **
+      ** If this is the first overflow page, then write a partial entry 
+      ** to the pointer-map. If we write nothing to this pointer-map slot,
+      ** then the optimistic overflow chain processing in clearCell()
+      ** may misinterpret the uninitialised values and delete the
+      ** wrong pages from the database.
+      */
+      if( pBt->autoVacuum && rc==SQLITE_OK ){
+        u8 eType = (pgnoPtrmap?PTRMAP_OVERFLOW2:PTRMAP_OVERFLOW1);
+        rc = ptrmapPut(pBt, pgnoOvfl, eType, pgnoPtrmap);
+        if( rc ){
+          releasePage(pOvfl);
+        }
+      }
+#endif
+      if( rc ){
+        releasePage(pToRelease);
+        return rc;
+      }
+      put4byte(pPrior, pgnoOvfl);
+      releasePage(pToRelease);
+      pToRelease = pOvfl;
+      pPrior = pOvfl->aData;
+      put4byte(pPrior, 0);
+      pPayload = &pOvfl->aData[4];
+      spaceLeft = pBt->usableSize - 4;
+    }
+    n = nPayload;
+    if( n>spaceLeft ) n = spaceLeft;
+    if( nSrc>0 ){
+      if( n>nSrc ) n = nSrc;
+      assert( pSrc );
+      memcpy(pPayload, pSrc, n);
+    }else{
+      memset(pPayload, 0, n);
+    }
+    nPayload -= n;
+    pPayload += n;
+    pSrc += n;
+    nSrc -= n;
+    spaceLeft -= n;
+    if( nSrc==0 ){
+      nSrc = nData;
+      pSrc = pData;
+    }
+  }
+  releasePage(pToRelease);
+  return SQLITE_OK;
+}
+
+/*
+** Change the MemPage.pParent pointer on the page whose number is
+** given in the second argument so that MemPage.pParent holds the
+** pointer in the third argument.
+*/
+static int reparentPage(BtShared *pBt, Pgno pgno, MemPage *pNewParent, int idx){
+  MemPage *pThis;
+  DbPage *pDbPage;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  assert( pNewParent!=0 );
+  if( pgno==0 ) return SQLITE_OK;
+  assert( pBt->pPager!=0 );
+  pDbPage = sqlite3PagerLookup(pBt->pPager, pgno);
+  if( pDbPage ){
+    pThis = (MemPage *)sqlite3PagerGetExtra(pDbPage);
+    if( pThis->isInit ){
+      assert( pThis->aData==sqlite3PagerGetData(pDbPage) );
+      if( pThis->pParent!=pNewParent ){
+        if( pThis->pParent ) sqlite3PagerUnref(pThis->pParent->pDbPage);
+        pThis->pParent = pNewParent;
+        sqlite3PagerRef(pNewParent->pDbPage);
+      }
+      pThis->idxParent = idx;
+    }
+    sqlite3PagerUnref(pDbPage);
+  }
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  if( pBt->autoVacuum ){
+    return ptrmapPut(pBt, pgno, PTRMAP_BTREE, pNewParent->pgno);
+  }
+#endif
+  return SQLITE_OK;
+}
+
+
+
+/*
+** Change the pParent pointer of all children of pPage to point back
+** to pPage.
+**
+** In other words, for every child of pPage, invoke reparentPage()
+** to make sure that each child knows that pPage is its parent.
+**
+** This routine gets called after you memcpy() one page into
+** another.
+*/
+static int reparentChildPages(MemPage *pPage){
+  int i;
+  BtShared *pBt = pPage->pBt;
+  int rc = SQLITE_OK;
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( pPage->leaf ) return SQLITE_OK;
+
+  for(i=0; i<pPage->nCell; i++){
+    u8 *pCell = findCell(pPage, i);
+    if( !pPage->leaf ){
+      rc = reparentPage(pBt, get4byte(pCell), pPage, i);
+      if( rc!=SQLITE_OK ) return rc;
+    }
+  }
+  if( !pPage->leaf ){
+    rc = reparentPage(pBt, get4byte(&pPage->aData[pPage->hdrOffset+8]), 
+       pPage, i);
+    pPage->idxShift = 0;
+  }
+  return rc;
+}
+
+/*
+** Remove the i-th cell from pPage.  This routine effects pPage only.
+** The cell content is not freed or deallocated.  It is assumed that
+** the cell content has been copied someplace else.  This routine just
+** removes the reference to the cell from pPage.
+**
+** "sz" must be the number of bytes in the cell.
+*/
+static void dropCell(MemPage *pPage, int idx, int sz){
+  int i;          /* Loop counter */
+  int pc;         /* Offset to cell content of cell being deleted */
+  u8 *data;       /* pPage->aData */
+  u8 *ptr;        /* Used to move bytes around within data[] */
+
+  assert( idx>=0 && idx<pPage->nCell );
+  assert( sz==cellSize(pPage, idx) );
+  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  data = pPage->aData;
+  ptr = &data[pPage->cellOffset + 2*idx];
+  pc = get2byte(ptr);
+  assert( pc>10 && pc+sz<=pPage->pBt->usableSize );
+  freeSpace(pPage, pc, sz);
+  for(i=idx+1; i<pPage->nCell; i++, ptr+=2){
+    ptr[0] = ptr[2];
+    ptr[1] = ptr[3];
+  }
+  pPage->nCell--;
+  put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
+  pPage->nFree += 2;
+  pPage->idxShift = 1;
+}
+
+/*
+** Insert a new cell on pPage at cell index "i".  pCell points to the
+** content of the cell.
+**
+** If the cell content will fit on the page, then put it there.  If it
+** will not fit, then make a copy of the cell content into pTemp if
+** pTemp is not null.  Regardless of pTemp, allocate a new entry
+** in pPage->aOvfl[] and make it point to the cell content (either
+** in pTemp or the original pCell) and also record its index. 
+** Allocating a new entry in pPage->aCell[] implies that 
+** pPage->nOverflow is incremented.
+**
+** If nSkip is non-zero, then do not copy the first nSkip bytes of the
+** cell. The caller will overwrite them after this function returns. If
+** nSkip is non-zero, then pCell may not point to an invalid memory location 
+** (but pCell+nSkip is always valid).
+*/
+static int insertCell(
+  MemPage *pPage,   /* Page into which we are copying */
+  int i,            /* New cell becomes the i-th cell of the page */
+  u8 *pCell,        /* Content of the new cell */
+  int sz,           /* Bytes of content in pCell */
+  u8 *pTemp,        /* Temp storage space for pCell, if needed */
+  u8 nSkip          /* Do not write the first nSkip bytes of the cell */
+){
+  int idx;          /* Where to write new cell content in data[] */
+  int j;            /* Loop counter */
+  int top;          /* First byte of content for any cell in data[] */
+  int end;          /* First byte past the last cell pointer in data[] */
+  int ins;          /* Index in data[] where new cell pointer is inserted */
+  int hdr;          /* Offset into data[] of the page header */
+  int cellOffset;   /* Address of first cell pointer in data[] */
+  u8 *data;         /* The content of the whole page */
+  u8 *ptr;          /* Used for moving information around in data[] */
+
+  assert( i>=0 && i<=pPage->nCell+pPage->nOverflow );
+  assert( sz==cellSizePtr(pPage, pCell) );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( pPage->nOverflow || sz+2>pPage->nFree ){
+    if( pTemp ){
+      memcpy(pTemp+nSkip, pCell+nSkip, sz-nSkip);
+      pCell = pTemp;
+    }
+    j = pPage->nOverflow++;
+    assert( j<sizeof(pPage->aOvfl)/sizeof(pPage->aOvfl[0]) );
+    pPage->aOvfl[j].pCell = pCell;
+    pPage->aOvfl[j].idx = i;
+    pPage->nFree = 0;
+  }else{
+    int rc = sqlite3PagerWrite(pPage->pDbPage);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    assert( sqlite3PagerIswriteable(pPage->pDbPage) );
+    data = pPage->aData;
+    hdr = pPage->hdrOffset;
+    top = get2byte(&data[hdr+5]);
+    cellOffset = pPage->cellOffset;
+    end = cellOffset + 2*pPage->nCell + 2;
+    ins = cellOffset + 2*i;
+    if( end > top - sz ){
+      rc = defragmentPage(pPage);
+      if( rc!=SQLITE_OK ) return rc;
+      top = get2byte(&data[hdr+5]);
+      assert( end + sz <= top );
+    }
+    idx = allocateSpace(pPage, sz);
+    assert( idx>0 );
+    assert( end <= get2byte(&data[hdr+5]) );
+    pPage->nCell++;
+    pPage->nFree -= 2;
+    memcpy(&data[idx+nSkip], pCell+nSkip, sz-nSkip);
+    for(j=end-2, ptr=&data[j]; j>ins; j-=2, ptr-=2){
+      ptr[0] = ptr[-2];
+      ptr[1] = ptr[-1];
+    }
+    put2byte(&data[ins], idx);
+    put2byte(&data[hdr+3], pPage->nCell);
+    pPage->idxShift = 1;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( pPage->pBt->autoVacuum ){
+      /* The cell may contain a pointer to an overflow page. If so, write
+      ** the entry for the overflow page into the pointer map.
+      */
+      CellInfo info;
+      sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+      assert( (info.nData+(pPage->intKey?0:info.nKey))==info.nPayload );
+      if( (info.nData+(pPage->intKey?0:info.nKey))>info.nLocal ){
+        Pgno pgnoOvfl = get4byte(&pCell[info.iOverflow]);
+        rc = ptrmapPut(pPage->pBt, pgnoOvfl, PTRMAP_OVERFLOW1, pPage->pgno);
+        if( rc!=SQLITE_OK ) return rc;
+      }
+    }
+#endif
+  }
+
+  return SQLITE_OK;
+}
+
+/*
+** Add a list of cells to a page.  The page should be initially empty.
+** The cells are guaranteed to fit on the page.
+*/
+static void assemblePage(
+  MemPage *pPage,   /* The page to be assemblied */
+  int nCell,        /* The number of cells to add to this page */
+  u8 **apCell,      /* Pointers to cell bodies */
+  int *aSize        /* Sizes of the cells */
+){
+  int i;            /* Loop counter */
+  int totalSize;    /* Total size of all cells */
+  int hdr;          /* Index of page header */
+  int cellptr;      /* Address of next cell pointer */
+  int cellbody;     /* Address of next cell body */
+  u8 *data;         /* Data for the page */
+
+  assert( pPage->nOverflow==0 );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  totalSize = 0;
+  for(i=0; i<nCell; i++){
+    totalSize += aSize[i];
+  }
+  assert( totalSize+2*nCell<=pPage->nFree );
+  assert( pPage->nCell==0 );
+  cellptr = pPage->cellOffset;
+  data = pPage->aData;
+  hdr = pPage->hdrOffset;
+  put2byte(&data[hdr+3], nCell);
+  if( nCell ){
+    cellbody = allocateSpace(pPage, totalSize);
+    assert( cellbody>0 );
+    assert( pPage->nFree >= 2*nCell );
+    pPage->nFree -= 2*nCell;
+    for(i=0; i<nCell; i++){
+      put2byte(&data[cellptr], cellbody);
+      memcpy(&data[cellbody], apCell[i], aSize[i]);
+      cellptr += 2;
+      cellbody += aSize[i];
+    }
+    assert( cellbody==pPage->pBt->usableSize );
+  }
+  pPage->nCell = nCell;
+}
+
+/*
+** The following parameters determine how many adjacent pages get involved
+** in a balancing operation.  NN is the number of neighbors on either side
+** of the page that participate in the balancing operation.  NB is the
+** total number of pages that participate, including the target page and
+** NN neighbors on either side.
+**
+** The minimum value of NN is 1 (of course).  Increasing NN above 1
+** (to 2 or 3) gives a modest improvement in SELECT and DELETE performance
+** in exchange for a larger degradation in INSERT and UPDATE performance.
+** The value of NN appears to give the best results overall.
+*/
+#define NN 1             /* Number of neighbors on either side of pPage */
+#define NB (NN*2+1)      /* Total pages involved in the balance */
+
+/* Forward reference */
+static int balance(MemPage*, int);
+
+#ifndef SQLITE_OMIT_QUICKBALANCE
+/*
+** This version of balance() handles the common special case where
+** a new entry is being inserted on the extreme right-end of the
+** tree, in other words, when the new entry will become the largest
+** entry in the tree.
+**
+** Instead of trying balance the 3 right-most leaf pages, just add
+** a new page to the right-hand side and put the one new entry in
+** that page.  This leaves the right side of the tree somewhat
+** unbalanced.  But odds are that we will be inserting new entries
+** at the end soon afterwards so the nearly empty page will quickly
+** fill up.  On average.
+**
+** pPage is the leaf page which is the right-most page in the tree.
+** pParent is its parent.  pPage must have a single overflow entry
+** which is also the right-most entry on the page.
+*/
+static int balance_quick(MemPage *pPage, MemPage *pParent){
+  int rc;
+  MemPage *pNew;
+  Pgno pgnoNew;
+  u8 *pCell;
+  int szCell;
+  CellInfo info;
+  BtShared *pBt = pPage->pBt;
+  int parentIdx = pParent->nCell;   /* pParent new divider cell index */
+  int parentSize;                   /* Size of new divider cell */
+  u8 parentCell[64];                /* Space for the new divider cell */
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+
+  /* Allocate a new page. Insert the overflow cell from pPage
+  ** into it. Then remove the overflow cell from pPage.
+  */
+  rc = allocateBtreePage(pBt, &pNew, &pgnoNew, 0, 0);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  pCell = pPage->aOvfl[0].pCell;
+  szCell = cellSizePtr(pPage, pCell);
+  zeroPage(pNew, pPage->aData[0]);
+  assemblePage(pNew, 1, &pCell, &szCell);
+  pPage->nOverflow = 0;
+
+  /* Set the parent of the newly allocated page to pParent. */
+  pNew->pParent = pParent;
+  sqlite3PagerRef(pParent->pDbPage);
+
+  /* pPage is currently the right-child of pParent. Change this
+  ** so that the right-child is the new page allocated above and
+  ** pPage is the next-to-right child. 
+  */
+  assert( pPage->nCell>0 );
+  pCell = findCell(pPage, pPage->nCell-1);
+  sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+  rc = fillInCell(pParent, parentCell, 0, info.nKey, 0, 0, 0, &parentSize);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  assert( parentSize<64 );
+  rc = insertCell(pParent, parentIdx, parentCell, parentSize, 0, 4);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  put4byte(findOverflowCell(pParent,parentIdx), pPage->pgno);
+  put4byte(&pParent->aData[pParent->hdrOffset+8], pgnoNew);
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  /* If this is an auto-vacuum database, update the pointer map
+  ** with entries for the new page, and any pointer from the 
+  ** cell on the page to an overflow page.
+  */
+  if( pBt->autoVacuum ){
+    rc = ptrmapPut(pBt, pgnoNew, PTRMAP_BTREE, pParent->pgno);
+    if( rc==SQLITE_OK ){
+      rc = ptrmapPutOvfl(pNew, 0);
+    }
+    if( rc!=SQLITE_OK ){
+      releasePage(pNew);
+      return rc;
+    }
+  }
+#endif
+
+  /* Release the reference to the new page and balance the parent page,
+  ** in case the divider cell inserted caused it to become overfull.
+  */
+  releasePage(pNew);
+  return balance(pParent, 0);
+}
+#endif /* SQLITE_OMIT_QUICKBALANCE */
+
+/*
+** This routine redistributes Cells on pPage and up to NN*2 siblings
+** of pPage so that all pages have about the same amount of free space.
+** Usually NN siblings on either side of pPage is used in the balancing,
+** though more siblings might come from one side if pPage is the first
+** or last child of its parent.  If pPage has fewer than 2*NN siblings
+** (something which can only happen if pPage is the root page or a 
+** child of root) then all available siblings participate in the balancing.
+**
+** The number of siblings of pPage might be increased or decreased by one or
+** two in an effort to keep pages nearly full but not over full. The root page
+** is special and is allowed to be nearly empty. If pPage is 
+** the root page, then the depth of the tree might be increased
+** or decreased by one, as necessary, to keep the root page from being
+** overfull or completely empty.
+**
+** Note that when this routine is called, some of the Cells on pPage
+** might not actually be stored in pPage->aData[].  This can happen
+** if the page is overfull.  Part of the job of this routine is to
+** make sure all Cells for pPage once again fit in pPage->aData[].
+**
+** In the course of balancing the siblings of pPage, the parent of pPage
+** might become overfull or underfull.  If that happens, then this routine
+** is called recursively on the parent.
+**
+** If this routine fails for any reason, it might leave the database
+** in a corrupted state.  So if this routine fails, the database should
+** be rolled back.
+*/
+static int balance_nonroot(MemPage *pPage){
+  MemPage *pParent;            /* The parent of pPage */
+  BtShared *pBt;               /* The whole database */
+  int nCell = 0;               /* Number of cells in apCell[] */
+  int nMaxCells = 0;           /* Allocated size of apCell, szCell, aFrom. */
+  int nOld;                    /* Number of pages in apOld[] */
+  int nNew;                    /* Number of pages in apNew[] */
+  int nDiv;                    /* Number of cells in apDiv[] */
+  int i, j, k;                 /* Loop counters */
+  int idx;                     /* Index of pPage in pParent->aCell[] */
+  int nxDiv;                   /* Next divider slot in pParent->aCell[] */
+  int rc;                      /* The return code */
+  int leafCorrection;          /* 4 if pPage is a leaf.  0 if not */
+  int leafData;                /* True if pPage is a leaf of a LEAFDATA tree */
+  int usableSpace;             /* Bytes in pPage beyond the header */
+  int pageFlags;               /* Value of pPage->aData[0] */
+  int subtotal;                /* Subtotal of bytes in cells on one page */
+  int iSpace = 0;              /* First unused byte of aSpace[] */
+  MemPage *apOld[NB];          /* pPage and up to two siblings */
+  Pgno pgnoOld[NB];            /* Page numbers for each page in apOld[] */
+  MemPage *apCopy[NB];         /* Private copies of apOld[] pages */
+  MemPage *apNew[NB+2];        /* pPage and up to NB siblings after balancing */
+  Pgno pgnoNew[NB+2];          /* Page numbers for each page in apNew[] */
+  u8 *apDiv[NB];               /* Divider cells in pParent */
+  int cntNew[NB+2];            /* Index in aCell[] of cell after i-th page */
+  int szNew[NB+2];             /* Combined size of cells place on i-th page */
+  u8 **apCell = 0;             /* All cells begin balanced */
+  int *szCell;                 /* Local size of all cells in apCell[] */
+  u8 *aCopy[NB];               /* Space for holding data of apCopy[] */
+  u8 *aSpace;                  /* Space to hold copies of dividers cells */
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  u8 *aFrom = 0;
+#endif
+
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+
+  /* 
+  ** Find the parent page.
+  */
+  assert( pPage->isInit );
+  assert( sqlite3PagerIswriteable(pPage->pDbPage) || pPage->nOverflow==1 );
+  pBt = pPage->pBt;
+  pParent = pPage->pParent;
+  assert( pParent );
+  if( SQLITE_OK!=(rc = sqlite3PagerWrite(pParent->pDbPage)) ){
+    return rc;
+  }
+  TRACE(("BALANCE: begin page %d child of %d\n", pPage->pgno, pParent->pgno));
+
+#ifndef SQLITE_OMIT_QUICKBALANCE
+  /*
+  ** A special case:  If a new entry has just been inserted into a
+  ** table (that is, a btree with integer keys and all data at the leaves)
+  ** and the new entry is the right-most entry in the tree (it has the
+  ** largest key) then use the special balance_quick() routine for
+  ** balancing.  balance_quick() is much faster and results in a tighter
+  ** packing of data in the common case.
+  */
+  if( pPage->leaf &&
+      pPage->intKey &&
+      pPage->leafData &&
+      pPage->nOverflow==1 &&
+      pPage->aOvfl[0].idx==pPage->nCell &&
+      pPage->pParent->pgno!=1 &&
+      get4byte(&pParent->aData[pParent->hdrOffset+8])==pPage->pgno
+  ){
+    /*
+    ** TODO: Check the siblings to the left of pPage. It may be that
+    ** they are not full and no new page is required.
+    */
+    return balance_quick(pPage, pParent);
+  }
+#endif
+
+  if( SQLITE_OK!=(rc = sqlite3PagerWrite(pPage->pDbPage)) ){
+    return rc;
+  }
+
+  /*
+  ** Find the cell in the parent page whose left child points back
+  ** to pPage.  The "idx" variable is the index of that cell.  If pPage
+  ** is the rightmost child of pParent then set idx to pParent->nCell 
+  */
+  if( pParent->idxShift ){
+    Pgno pgno;
+    pgno = pPage->pgno;
+    assert( pgno==sqlite3PagerPagenumber(pPage->pDbPage) );
+    for(idx=0; idx<pParent->nCell; idx++){
+      if( get4byte(findCell(pParent, idx))==pgno ){
+        break;
+      }
+    }
+    assert( idx<pParent->nCell
+             || get4byte(&pParent->aData[pParent->hdrOffset+8])==pgno );
+  }else{
+    idx = pPage->idxParent;
+  }
+
+  /*
+  ** Initialize variables so that it will be safe to jump
+  ** directly to balance_cleanup at any moment.
+  */
+  nOld = nNew = 0;
+  sqlite3PagerRef(pParent->pDbPage);
+
+  /*
+  ** Find sibling pages to pPage and the cells in pParent that divide
+  ** the siblings.  An attempt is made to find NN siblings on either
+  ** side of pPage.  More siblings are taken from one side, however, if
+  ** pPage there are fewer than NN siblings on the other side.  If pParent
+  ** has NB or fewer children then all children of pParent are taken.
+  */
+  nxDiv = idx - NN;
+  if( nxDiv + NB > pParent->nCell ){
+    nxDiv = pParent->nCell - NB + 1;
+  }
+  if( nxDiv<0 ){
+    nxDiv = 0;
+  }
+  nDiv = 0;
+  for(i=0, k=nxDiv; i<NB; i++, k++){
+    if( k<pParent->nCell ){
+      apDiv[i] = findCell(pParent, k);
+      nDiv++;
+      assert( !pParent->leaf );
+      pgnoOld[i] = get4byte(apDiv[i]);
+    }else if( k==pParent->nCell ){
+      pgnoOld[i] = get4byte(&pParent->aData[pParent->hdrOffset+8]);
+    }else{
+      break;
+    }
+    rc = getAndInitPage(pBt, pgnoOld[i], &apOld[i], pParent);
+    if( rc ) goto balance_cleanup;
+    apOld[i]->idxParent = k;
+    apCopy[i] = 0;
+    assert( i==nOld );
+    nOld++;
+    nMaxCells += 1+apOld[i]->nCell+apOld[i]->nOverflow;
+  }
+
+  /* Make nMaxCells a multiple of 2 in order to preserve 8-byte
+  ** alignment */
+  nMaxCells = (nMaxCells + 1)&~1;
+
+  /*
+  ** Allocate space for memory structures
+  */
+  apCell = sqlite3_malloc( 
+       nMaxCells*sizeof(u8*)                           /* apCell */
+     + nMaxCells*sizeof(int)                           /* szCell */
+     + ROUND8(sizeof(MemPage))*NB                      /* aCopy */
+     + pBt->pageSize*(5+NB)                            /* aSpace */
+     + (ISAUTOVACUUM ? nMaxCells : 0)                  /* aFrom */
+  );
+  if( apCell==0 ){
+    rc = SQLITE_NOMEM;
+    goto balance_cleanup;
+  }
+  szCell = (int*)&apCell[nMaxCells];
+  aCopy[0] = (u8*)&szCell[nMaxCells];
+  assert( ((aCopy[0] - (u8*)apCell) & 7)==0 ); /* 8-byte alignment required */
+  for(i=1; i<NB; i++){
+    aCopy[i] = &aCopy[i-1][pBt->pageSize+ROUND8(sizeof(MemPage))];
+    assert( ((aCopy[i] - (u8*)apCell) & 7)==0 ); /* 8-byte alignment required */
+  }
+  aSpace = &aCopy[NB-1][pBt->pageSize+ROUND8(sizeof(MemPage))];
+  assert( ((aSpace - (u8*)apCell) & 7)==0 ); /* 8-byte alignment required */
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  if( pBt->autoVacuum ){
+    aFrom = &aSpace[5*pBt->pageSize];
+  }
+#endif
+  
+  /*
+  ** Make copies of the content of pPage and its siblings into aOld[].
+  ** The rest of this function will use data from the copies rather
+  ** that the original pages since the original pages will be in the
+  ** process of being overwritten.
+  */
+  for(i=0; i<nOld; i++){
+    MemPage *p = apCopy[i] = (MemPage*)aCopy[i];
+    memcpy(p, apOld[i], sizeof(MemPage));
+    p->aData = (void*)&p[1];
+    memcpy(p->aData, apOld[i]->aData, pBt->pageSize);
+  }
+
+  /*
+  ** Load pointers to all cells on sibling pages and the divider cells
+  ** into the local apCell[] array.  Make copies of the divider cells
+  ** into space obtained form aSpace[] and remove the the divider Cells
+  ** from pParent.
+  **
+  ** If the siblings are on leaf pages, then the child pointers of the
+  ** divider cells are stripped from the cells before they are copied
+  ** into aSpace[].  In this way, all cells in apCell[] are without
+  ** child pointers.  If siblings are not leaves, then all cell in
+  ** apCell[] include child pointers.  Either way, all cells in apCell[]
+  ** are alike.
+  **
+  ** leafCorrection:  4 if pPage is a leaf.  0 if pPage is not a leaf.
+  **       leafData:  1 if pPage holds key+data and pParent holds only keys.
+  */
+  nCell = 0;
+  leafCorrection = pPage->leaf*4;
+  leafData = pPage->leafData && pPage->leaf;
+  for(i=0; i<nOld; i++){
+    MemPage *pOld = apCopy[i];
+    int limit = pOld->nCell+pOld->nOverflow;
+    for(j=0; j<limit; j++){
+      assert( nCell<nMaxCells );
+      apCell[nCell] = findOverflowCell(pOld, j);
+      szCell[nCell] = cellSizePtr(pOld, apCell[nCell]);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      if( pBt->autoVacuum ){
+        int a;
+        aFrom[nCell] = i;
+        for(a=0; a<pOld->nOverflow; a++){
+          if( pOld->aOvfl[a].pCell==apCell[nCell] ){
+            aFrom[nCell] = 0xFF;
+            break;
+          }
+        }
+      }
+#endif
+      nCell++;
+    }
+    if( i<nOld-1 ){
+      int sz = cellSizePtr(pParent, apDiv[i]);
+      if( leafData ){
+        /* With the LEAFDATA flag, pParent cells hold only INTKEYs that
+        ** are duplicates of keys on the child pages.  We need to remove
+        ** the divider cells from pParent, but the dividers cells are not
+        ** added to apCell[] because they are duplicates of child cells.
+        */
+        dropCell(pParent, nxDiv, sz);
+      }else{
+        u8 *pTemp;
+        assert( nCell<nMaxCells );
+        szCell[nCell] = sz;
+        pTemp = &aSpace[iSpace];
+        iSpace += sz;
+        assert( iSpace<=pBt->pageSize*5 );
+        memcpy(pTemp, apDiv[i], sz);
+        apCell[nCell] = pTemp+leafCorrection;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+        if( pBt->autoVacuum ){
+          aFrom[nCell] = 0xFF;
+        }
+#endif
+        dropCell(pParent, nxDiv, sz);
+        szCell[nCell] -= leafCorrection;
+        assert( get4byte(pTemp)==pgnoOld[i] );
+        if( !pOld->leaf ){
+          assert( leafCorrection==0 );
+          /* The right pointer of the child page pOld becomes the left
+          ** pointer of the divider cell */
+          memcpy(apCell[nCell], &pOld->aData[pOld->hdrOffset+8], 4);
+        }else{
+          assert( leafCorrection==4 );
+          if( szCell[nCell]<4 ){
+            /* Do not allow any cells smaller than 4 bytes. */
+            szCell[nCell] = 4;
+          }
+        }
+        nCell++;
+      }
+    }
+  }
+
+  /*
+  ** Figure out the number of pages needed to hold all nCell cells.
+  ** Store this number in "k".  Also compute szNew[] which is the total
+  ** size of all cells on the i-th page and cntNew[] which is the index
+  ** in apCell[] of the cell that divides page i from page i+1.  
+  ** cntNew[k] should equal nCell.
+  **
+  ** Values computed by this block:
+  **
+  **           k: The total number of sibling pages
+  **    szNew[i]: Spaced used on the i-th sibling page.
+  **   cntNew[i]: Index in apCell[] and szCell[] for the first cell to
+  **              the right of the i-th sibling page.
+  ** usableSpace: Number of bytes of space available on each sibling.
+  ** 
+  */
+  usableSpace = pBt->usableSize - 12 + leafCorrection;
+  for(subtotal=k=i=0; i<nCell; i++){
+    assert( i<nMaxCells );
+    subtotal += szCell[i] + 2;
+    if( subtotal > usableSpace ){
+      szNew[k] = subtotal - szCell[i];
+      cntNew[k] = i;
+      if( leafData ){ i--; }
+      subtotal = 0;
+      k++;
+    }
+  }
+  szNew[k] = subtotal;
+  cntNew[k] = nCell;
+  k++;
+
+  /*
+  ** The packing computed by the previous block is biased toward the siblings
+  ** on the left side.  The left siblings are always nearly full, while the
+  ** right-most sibling might be nearly empty.  This block of code attempts
+  ** to adjust the packing of siblings to get a better balance.
+  **
+  ** This adjustment is more than an optimization.  The packing above might
+  ** be so out of balance as to be illegal.  For example, the right-most
+  ** sibling might be completely empty.  This adjustment is not optional.
+  */
+  for(i=k-1; i>0; i--){
+    int szRight = szNew[i];  /* Size of sibling on the right */
+    int szLeft = szNew[i-1]; /* Size of sibling on the left */
+    int r;              /* Index of right-most cell in left sibling */
+    int d;              /* Index of first cell to the left of right sibling */
+
+    r = cntNew[i-1] - 1;
+    d = r + 1 - leafData;
+    assert( d<nMaxCells );
+    assert( r<nMaxCells );
+    while( szRight==0 || szRight+szCell[d]+2<=szLeft-(szCell[r]+2) ){
+      szRight += szCell[d] + 2;
+      szLeft -= szCell[r] + 2;
+      cntNew[i-1]--;
+      r = cntNew[i-1] - 1;
+      d = r + 1 - leafData;
+    }
+    szNew[i] = szRight;
+    szNew[i-1] = szLeft;
+  }
+
+  /* Either we found one or more cells (cntnew[0])>0) or we are the
+  ** a virtual root page.  A virtual root page is when the real root
+  ** page is page 1 and we are the only child of that page.
+  */
+  assert( cntNew[0]>0 || (pParent->pgno==1 && pParent->nCell==0) );
+
+  /*
+  ** Allocate k new pages.  Reuse old pages where possible.
+  */
+  assert( pPage->pgno>1 );
+  pageFlags = pPage->aData[0];
+  for(i=0; i<k; i++){
+    MemPage *pNew;
+    if( i<nOld ){
+      pNew = apNew[i] = apOld[i];
+      pgnoNew[i] = pgnoOld[i];
+      apOld[i] = 0;
+      rc = sqlite3PagerWrite(pNew->pDbPage);
+      nNew++;
+      if( rc ) goto balance_cleanup;
+    }else{
+      assert( i>0 );
+      rc = allocateBtreePage(pBt, &pNew, &pgnoNew[i], pgnoNew[i-1], 0);
+      if( rc ) goto balance_cleanup;
+      apNew[i] = pNew;
+      nNew++;
+    }
+    zeroPage(pNew, pageFlags);
+  }
+
+  /* Free any old pages that were not reused as new pages.
+  */
+  while( i<nOld ){
+    rc = freePage(apOld[i]);
+    if( rc ) goto balance_cleanup;
+    releasePage(apOld[i]);
+    apOld[i] = 0;
+    i++;
+  }
+
+  /*
+  ** Put the new pages in accending order.  This helps to
+  ** keep entries in the disk file in order so that a scan
+  ** of the table is a linear scan through the file.  That
+  ** in turn helps the operating system to deliver pages
+  ** from the disk more rapidly.
+  **
+  ** An O(n^2) insertion sort algorithm is used, but since
+  ** n is never more than NB (a small constant), that should
+  ** not be a problem.
+  **
+  ** When NB==3, this one optimization makes the database
+  ** about 25% faster for large insertions and deletions.
+  */
+  for(i=0; i<k-1; i++){
+    int minV = pgnoNew[i];
+    int minI = i;
+    for(j=i+1; j<k; j++){
+      if( pgnoNew[j]<(unsigned)minV ){
+        minI = j;
+        minV = pgnoNew[j];
+      }
+    }
+    if( minI>i ){
+      int t;
+      MemPage *pT;
+      t = pgnoNew[i];
+      pT = apNew[i];
+      pgnoNew[i] = pgnoNew[minI];
+      apNew[i] = apNew[minI];
+      pgnoNew[minI] = t;
+      apNew[minI] = pT;
+    }
+  }
+  TRACE(("BALANCE: old: %d %d %d  new: %d(%d) %d(%d) %d(%d) %d(%d) %d(%d)\n",
+    pgnoOld[0], 
+    nOld>=2 ? pgnoOld[1] : 0,
+    nOld>=3 ? pgnoOld[2] : 0,
+    pgnoNew[0], szNew[0],
+    nNew>=2 ? pgnoNew[1] : 0, nNew>=2 ? szNew[1] : 0,
+    nNew>=3 ? pgnoNew[2] : 0, nNew>=3 ? szNew[2] : 0,
+    nNew>=4 ? pgnoNew[3] : 0, nNew>=4 ? szNew[3] : 0,
+    nNew>=5 ? pgnoNew[4] : 0, nNew>=5 ? szNew[4] : 0));
+
+  /*
+  ** Evenly distribute the data in apCell[] across the new pages.
+  ** Insert divider cells into pParent as necessary.
+  */
+  j = 0;
+  for(i=0; i<nNew; i++){
+    /* Assemble the new sibling page. */
+    MemPage *pNew = apNew[i];
+    assert( j<nMaxCells );
+    assert( pNew->pgno==pgnoNew[i] );
+    assemblePage(pNew, cntNew[i]-j, &apCell[j], &szCell[j]);
+    assert( pNew->nCell>0 || (nNew==1 && cntNew[0]==0) );
+    assert( pNew->nOverflow==0 );
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    /* If this is an auto-vacuum database, update the pointer map entries
+    ** that point to the siblings that were rearranged. These can be: left
+    ** children of cells, the right-child of the page, or overflow pages
+    ** pointed to by cells.
+    */
+    if( pBt->autoVacuum ){
+      for(k=j; k<cntNew[i]; k++){
+        assert( k<nMaxCells );
+        if( aFrom[k]==0xFF || apCopy[aFrom[k]]->pgno!=pNew->pgno ){
+          rc = ptrmapPutOvfl(pNew, k-j);
+          if( rc!=SQLITE_OK ){
+            goto balance_cleanup;
+          }
+        }
+      }
+    }
+#endif
+
+    j = cntNew[i];
+
+    /* If the sibling page assembled above was not the right-most sibling,
+    ** insert a divider cell into the parent page.
+    */
+    if( i<nNew-1 && j<nCell ){
+      u8 *pCell;
+      u8 *pTemp;
+      int sz;
+
+      assert( j<nMaxCells );
+      pCell = apCell[j];
+      sz = szCell[j] + leafCorrection;
+      if( !pNew->leaf ){
+        memcpy(&pNew->aData[8], pCell, 4);
+        pTemp = 0;
+      }else if( leafData ){
+        /* If the tree is a leaf-data tree, and the siblings are leaves, 
+        ** then there is no divider cell in apCell[]. Instead, the divider 
+        ** cell consists of the integer key for the right-most cell of 
+        ** the sibling-page assembled above only.
+        */
+        CellInfo info;
+        j--;
+        sqlite3BtreeParseCellPtr(pNew, apCell[j], &info);
+        pCell = &aSpace[iSpace];
+        fillInCell(pParent, pCell, 0, info.nKey, 0, 0, 0, &sz);
+        iSpace += sz;
+        assert( iSpace<=pBt->pageSize*5 );
+        pTemp = 0;
+      }else{
+        pCell -= 4;
+        pTemp = &aSpace[iSpace];
+        iSpace += sz;
+        assert( iSpace<=pBt->pageSize*5 );
+        /* Obscure case for non-leaf-data trees: If the cell at pCell was
+        ** previously stored on a leaf node, and it's reported size was 4
+        ** bytes, then it may actually be smaller than this 
+        ** (see sqlite3BtreeParseCellPtr(), 4 bytes is the minimum size of
+        ** any cell). But it's important to pass the correct size to 
+        ** insertCell(), so reparse the cell now.
+        **
+        ** Note that this can never happen in an SQLite data file, as all
+        ** cells are at least 4 bytes. It only happens in b-trees used
+        ** to evaluate "IN (SELECT ...)" and similar clauses.
+        */
+        if( szCell[j]==4 ){
+          assert(leafCorrection==4);
+          sz = cellSizePtr(pParent, pCell);
+        }
+      }
+      rc = insertCell(pParent, nxDiv, pCell, sz, pTemp, 4);
+      if( rc!=SQLITE_OK ) goto balance_cleanup;
+      put4byte(findOverflowCell(pParent,nxDiv), pNew->pgno);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      /* If this is an auto-vacuum database, and not a leaf-data tree,
+      ** then update the pointer map with an entry for the overflow page
+      ** that the cell just inserted points to (if any).
+      */
+      if( pBt->autoVacuum && !leafData ){
+        rc = ptrmapPutOvfl(pParent, nxDiv);
+        if( rc!=SQLITE_OK ){
+          goto balance_cleanup;
+        }
+      }
+#endif
+      j++;
+      nxDiv++;
+    }
+  }
+  assert( j==nCell );
+  assert( nOld>0 );
+  assert( nNew>0 );
+  if( (pageFlags & PTF_LEAF)==0 ){
+    memcpy(&apNew[nNew-1]->aData[8], &apCopy[nOld-1]->aData[8], 4);
+  }
+  if( nxDiv==pParent->nCell+pParent->nOverflow ){
+    /* Right-most sibling is the right-most child of pParent */
+    put4byte(&pParent->aData[pParent->hdrOffset+8], pgnoNew[nNew-1]);
+  }else{
+    /* Right-most sibling is the left child of the first entry in pParent
+    ** past the right-most divider entry */
+    put4byte(findOverflowCell(pParent, nxDiv), pgnoNew[nNew-1]);
+  }
+
+  /*
+  ** Reparent children of all cells.
+  */
+  for(i=0; i<nNew; i++){
+    rc = reparentChildPages(apNew[i]);
+    if( rc!=SQLITE_OK ) goto balance_cleanup;
+  }
+  rc = reparentChildPages(pParent);
+  if( rc!=SQLITE_OK ) goto balance_cleanup;
+
+  /*
+  ** Balance the parent page.  Note that the current page (pPage) might
+  ** have been added to the freelist so it might no longer be initialized.
+  ** But the parent page will always be initialized.
+  */
+  assert( pParent->isInit );
+  rc = balance(pParent, 0);
+  
+  /*
+  ** Cleanup before returning.
+  */
+balance_cleanup:
+  sqlite3_free(apCell);
+  for(i=0; i<nOld; i++){
+    releasePage(apOld[i]);
+  }
+  for(i=0; i<nNew; i++){
+    releasePage(apNew[i]);
+  }
+  releasePage(pParent);
+  TRACE(("BALANCE: finished with %d: old=%d new=%d cells=%d\n",
+          pPage->pgno, nOld, nNew, nCell));
+  return rc;
+}
+
+/*
+** This routine is called for the root page of a btree when the root
+** page contains no cells.  This is an opportunity to make the tree
+** shallower by one level.
+*/
+static int balance_shallower(MemPage *pPage){
+  MemPage *pChild;             /* The only child page of pPage */
+  Pgno pgnoChild;              /* Page number for pChild */
+  int rc = SQLITE_OK;          /* Return code from subprocedures */
+  BtShared *pBt;                  /* The main BTree structure */
+  int mxCellPerPage;           /* Maximum number of cells per page */
+  u8 **apCell;                 /* All cells from pages being balanced */
+  int *szCell;                 /* Local size of all cells */
+
+  assert( pPage->pParent==0 );
+  assert( pPage->nCell==0 );
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  pBt = pPage->pBt;
+  mxCellPerPage = MX_CELL(pBt);
+  apCell = sqlite3_malloc( mxCellPerPage*(sizeof(u8*)+sizeof(int)) );
+  if( apCell==0 ) return SQLITE_NOMEM;
+  szCell = (int*)&apCell[mxCellPerPage];
+  if( pPage->leaf ){
+    /* The table is completely empty */
+    TRACE(("BALANCE: empty table %d\n", pPage->pgno));
+  }else{
+    /* The root page is empty but has one child.  Transfer the
+    ** information from that one child into the root page if it 
+    ** will fit.  This reduces the depth of the tree by one.
+    **
+    ** If the root page is page 1, it has less space available than
+    ** its child (due to the 100 byte header that occurs at the beginning
+    ** of the database fle), so it might not be able to hold all of the 
+    ** information currently contained in the child.  If this is the 
+    ** case, then do not do the transfer.  Leave page 1 empty except
+    ** for the right-pointer to the child page.  The child page becomes
+    ** the virtual root of the tree.
+    */
+    pgnoChild = get4byte(&pPage->aData[pPage->hdrOffset+8]);
+    assert( pgnoChild>0 );
+    assert( pgnoChild<=sqlite3PagerPagecount(pPage->pBt->pPager) );
+    rc = sqlite3BtreeGetPage(pPage->pBt, pgnoChild, &pChild, 0);
+    if( rc ) goto end_shallow_balance;
+    if( pPage->pgno==1 ){
+      rc = sqlite3BtreeInitPage(pChild, pPage);
+      if( rc ) goto end_shallow_balance;
+      assert( pChild->nOverflow==0 );
+      if( pChild->nFree>=100 ){
+        /* The child information will fit on the root page, so do the
+        ** copy */
+        int i;
+        zeroPage(pPage, pChild->aData[0]);
+        for(i=0; i<pChild->nCell; i++){
+          apCell[i] = findCell(pChild,i);
+          szCell[i] = cellSizePtr(pChild, apCell[i]);
+        }
+        assemblePage(pPage, pChild->nCell, apCell, szCell);
+        /* Copy the right-pointer of the child to the parent. */
+        put4byte(&pPage->aData[pPage->hdrOffset+8], 
+            get4byte(&pChild->aData[pChild->hdrOffset+8]));
+        freePage(pChild);
+        TRACE(("BALANCE: child %d transfer to page 1\n", pChild->pgno));
+      }else{
+        /* The child has more information that will fit on the root.
+        ** The tree is already balanced.  Do nothing. */
+        TRACE(("BALANCE: child %d will not fit on page 1\n", pChild->pgno));
+      }
+    }else{
+      memcpy(pPage->aData, pChild->aData, pPage->pBt->usableSize);
+      pPage->isInit = 0;
+      pPage->pParent = 0;
+      rc = sqlite3BtreeInitPage(pPage, 0);
+      assert( rc==SQLITE_OK );
+      freePage(pChild);
+      TRACE(("BALANCE: transfer child %d into root %d\n",
+              pChild->pgno, pPage->pgno));
+    }
+    rc = reparentChildPages(pPage);
+    assert( pPage->nOverflow==0 );
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( pBt->autoVacuum ){
+      int i;
+      for(i=0; i<pPage->nCell; i++){ 
+        rc = ptrmapPutOvfl(pPage, i);
+        if( rc!=SQLITE_OK ){
+          goto end_shallow_balance;
+        }
+      }
+    }
+#endif
+    releasePage(pChild);
+  }
+end_shallow_balance:
+  sqlite3_free(apCell);
+  return rc;
+}
+
+
+/*
+** The root page is overfull
+**
+** When this happens, Create a new child page and copy the
+** contents of the root into the child.  Then make the root
+** page an empty page with rightChild pointing to the new
+** child.   Finally, call balance_internal() on the new child
+** to cause it to split.
+*/
+static int balance_deeper(MemPage *pPage){
+  int rc;             /* Return value from subprocedures */
+  MemPage *pChild;    /* Pointer to a new child page */
+  Pgno pgnoChild;     /* Page number of the new child page */
+  BtShared *pBt;         /* The BTree */
+  int usableSize;     /* Total usable size of a page */
+  u8 *data;           /* Content of the parent page */
+  u8 *cdata;          /* Content of the child page */
+  int hdr;            /* Offset to page header in parent */
+  int brk;            /* Offset to content of first cell in parent */
+
+  assert( pPage->pParent==0 );
+  assert( pPage->nOverflow>0 );
+  pBt = pPage->pBt;
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  rc = allocateBtreePage(pBt, &pChild, &pgnoChild, pPage->pgno, 0);
+  if( rc ) return rc;
+  assert( sqlite3PagerIswriteable(pChild->pDbPage) );
+  usableSize = pBt->usableSize;
+  data = pPage->aData;
+  hdr = pPage->hdrOffset;
+  brk = get2byte(&data[hdr+5]);
+  cdata = pChild->aData;
+  memcpy(cdata, &data[hdr], pPage->cellOffset+2*pPage->nCell-hdr);
+  memcpy(&cdata[brk], &data[brk], usableSize-brk);
+  assert( pChild->isInit==0 );
+  rc = sqlite3BtreeInitPage(pChild, pPage);
+  if( rc ) goto balancedeeper_out;
+  memcpy(pChild->aOvfl, pPage->aOvfl, pPage->nOverflow*sizeof(pPage->aOvfl[0]));
+  pChild->nOverflow = pPage->nOverflow;
+  if( pChild->nOverflow ){
+    pChild->nFree = 0;
+  }
+  assert( pChild->nCell==pPage->nCell );
+  zeroPage(pPage, pChild->aData[0] & ~PTF_LEAF);
+  put4byte(&pPage->aData[pPage->hdrOffset+8], pgnoChild);
+  TRACE(("BALANCE: copy root %d into %d\n", pPage->pgno, pChild->pgno));
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  if( pBt->autoVacuum ){
+    int i;
+    rc = ptrmapPut(pBt, pChild->pgno, PTRMAP_BTREE, pPage->pgno);
+    if( rc ) goto balancedeeper_out;
+    for(i=0; i<pChild->nCell; i++){
+      rc = ptrmapPutOvfl(pChild, i);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+    }
+  }
+#endif
+  rc = balance_nonroot(pChild);
+
+balancedeeper_out:
+  releasePage(pChild);
+  return rc;
+}
+
+/*
+** Decide if the page pPage needs to be balanced.  If balancing is
+** required, call the appropriate balancing routine.
+*/
+static int balance(MemPage *pPage, int insert){
+  int rc = SQLITE_OK;
+  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
+  if( pPage->pParent==0 ){
+    rc = sqlite3PagerWrite(pPage->pDbPage);
+    if( rc==SQLITE_OK && pPage->nOverflow>0 ){
+      rc = balance_deeper(pPage);
+    }
+    if( rc==SQLITE_OK && pPage->nCell==0 ){
+      rc = balance_shallower(pPage);
+    }
+  }else{
+    if( pPage->nOverflow>0 || 
+        (!insert && pPage->nFree>pPage->pBt->usableSize*2/3) ){
+      rc = balance_nonroot(pPage);
+    }
+  }
+  return rc;
+}
+
+/*
+** This routine checks all cursors that point to table pgnoRoot.
+** If any of those cursors were opened with wrFlag==0 in a different
+** database connection (a database connection that shares the pager
+** cache with the current connection) and that other connection 
+** is not in the ReadUncommmitted state, then this routine returns 
+** SQLITE_LOCKED.
+**
+** In addition to checking for read-locks (where a read-lock 
+** means a cursor opened with wrFlag==0) this routine also moves
+** all write cursors so that they are pointing to the 
+** first Cell on the root page.  This is necessary because an insert 
+** or delete might change the number of cells on a page or delete
+** a page entirely and we do not want to leave any cursors 
+** pointing to non-existant pages or cells.
+*/
+static int checkReadLocks(Btree *pBtree, Pgno pgnoRoot, BtCursor *pExclude){
+  BtCursor *p;
+  BtShared *pBt = pBtree->pBt;
+  sqlite3 *db = pBtree->pSqlite;
+  assert( sqlite3BtreeHoldsMutex(pBtree) );
+  for(p=pBt->pCursor; p; p=p->pNext){
+    if( p==pExclude ) continue;
+    if( p->eState!=CURSOR_VALID ) continue;
+    if( p->pgnoRoot!=pgnoRoot ) continue;
+    if( p->wrFlag==0 ){
+      sqlite3 *dbOther = p->pBtree->pSqlite;
+      if( dbOther==0 ||
+         (dbOther!=db && (dbOther->flags & SQLITE_ReadUncommitted)==0) ){
+        return SQLITE_LOCKED;
+      }
+    }else if( p->pPage->pgno!=p->pgnoRoot ){
+      moveToRoot(p);
+    }
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Insert a new record into the BTree.  The key is given by (pKey,nKey)
+** and the data is given by (pData,nData).  The cursor is used only to
+** define what table the record should be inserted into.  The cursor
+** is left pointing at a random location.
+**
+** For an INTKEY table, only the nKey value of the key is used.  pKey is
+** ignored.  For a ZERODATA table, the pData and nData are both ignored.
+*/
+int sqlite3BtreeInsert(
+  BtCursor *pCur,                /* Insert data into the table of this cursor */
+  const void *pKey, i64 nKey,    /* The key of the new record */
+  const void *pData, int nData,  /* The data of the new record */
+  int nZero,                     /* Number of extra 0 bytes to append to data */
+  int appendBias                 /* True if this is likely an append */
+){
+  int rc;
+  int loc;
+  int szNew;
+  MemPage *pPage;
+  Btree *p = pCur->pBtree;
+  BtShared *pBt = p->pBt;
+  unsigned char *oldCell;
+  unsigned char *newCell = 0;
+
+  assert( cursorHoldsMutex(pCur) );
+  if( pBt->inTransaction!=TRANS_WRITE ){
+    /* Must start a transaction before doing an insert */
+    rc = pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+    return rc;
+  }
+  assert( !pBt->readOnly );
+  if( !pCur->wrFlag ){
+    return SQLITE_PERM;   /* Cursor not open for writing */
+  }
+  if( checkReadLocks(pCur->pBtree, pCur->pgnoRoot, pCur) ){
+    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
+  }
+  if( pCur->eState==CURSOR_FAULT ){
+    return pCur->skip;
+  }
+
+  /* Save the positions of any other cursors open on this table */
+  clearCursorPosition(pCur);
+  if( 
+    SQLITE_OK!=(rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur)) ||
+    SQLITE_OK!=(rc = sqlite3BtreeMoveto(pCur, pKey, nKey, appendBias, &loc))
+  ){
+    return rc;
+  }
+
+  pPage = pCur->pPage;
+  assert( pPage->intKey || nKey>=0 );
+  assert( pPage->leaf || !pPage->leafData );
+  TRACE(("INSERT: table=%d nkey=%lld ndata=%d page=%d %s\n",
+          pCur->pgnoRoot, nKey, nData, pPage->pgno,
+          loc==0 ? "overwrite" : "new entry"));
+  assert( pPage->isInit );
+  newCell = sqlite3_malloc( MX_CELL_SIZE(pBt) );
+  if( newCell==0 ) return SQLITE_NOMEM;
+  rc = fillInCell(pPage, newCell, pKey, nKey, pData, nData, nZero, &szNew);
+  if( rc ) goto end_insert;
+  assert( szNew==cellSizePtr(pPage, newCell) );
+  assert( szNew<=MX_CELL_SIZE(pBt) );
+  if( loc==0 && CURSOR_VALID==pCur->eState ){
+    int szOld;
+    assert( pCur->idx>=0 && pCur->idx<pPage->nCell );
+    rc = sqlite3PagerWrite(pPage->pDbPage);
+    if( rc ){
+      goto end_insert;
+    }
+    oldCell = findCell(pPage, pCur->idx);
+    if( !pPage->leaf ){
+      memcpy(newCell, oldCell, 4);
+    }
+    szOld = cellSizePtr(pPage, oldCell);
+    rc = clearCell(pPage, oldCell);
+    if( rc ) goto end_insert;
+    dropCell(pPage, pCur->idx, szOld);
+  }else if( loc<0 && pPage->nCell>0 ){
+    assert( pPage->leaf );
+    pCur->idx++;
+    pCur->info.nSize = 0;
+  }else{
+    assert( pPage->leaf );
+  }
+  rc = insertCell(pPage, pCur->idx, newCell, szNew, 0, 0);
+  if( rc!=SQLITE_OK ) goto end_insert;
+  rc = balance(pPage, 1);
+  /* sqlite3BtreePageDump(pCur->pBt, pCur->pgnoRoot, 1); */
+  /* fflush(stdout); */
+  if( rc==SQLITE_OK ){
+    moveToRoot(pCur);
+  }
+end_insert:
+  sqlite3_free(newCell);
+  return rc;
+}
+
+/*
+** Delete the entry that the cursor is pointing to.  The cursor
+** is left pointing at a random location.
+*/
+int sqlite3BtreeDelete(BtCursor *pCur){
+  MemPage *pPage = pCur->pPage;
+  unsigned char *pCell;
+  int rc;
+  Pgno pgnoChild = 0;
+  Btree *p = pCur->pBtree;
+  BtShared *pBt = p->pBt;
+
+  assert( cursorHoldsMutex(pCur) );
+  assert( pPage->isInit );
+  if( pBt->inTransaction!=TRANS_WRITE ){
+    /* Must start a transaction before doing a delete */
+    rc = pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+    return rc;
+  }
+  assert( !pBt->readOnly );
+  if( pCur->eState==CURSOR_FAULT ){
+    return pCur->skip;
+  }
+  if( pCur->idx >= pPage->nCell ){
+    return SQLITE_ERROR;  /* The cursor is not pointing to anything */
+  }
+  if( !pCur->wrFlag ){
+    return SQLITE_PERM;   /* Did not open this cursor for writing */
+  }
+  if( checkReadLocks(pCur->pBtree, pCur->pgnoRoot, pCur) ){
+    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
+  }
+
+  /* Restore the current cursor position (a no-op if the cursor is not in 
+  ** CURSOR_REQUIRESEEK state) and save the positions of any other cursors 
+  ** open on the same table. Then call sqlite3PagerWrite() on the page
+  ** that the entry will be deleted from.
+  */
+  if( 
+    (rc = restoreOrClearCursorPosition(pCur))!=0 ||
+    (rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur))!=0 ||
+    (rc = sqlite3PagerWrite(pPage->pDbPage))!=0
+  ){
+    return rc;
+  }
+
+  /* Locate the cell within it's page and leave pCell pointing to the
+  ** data. The clearCell() call frees any overflow pages associated with the
+  ** cell. The cell itself is still intact.
+  */
+  pCell = findCell(pPage, pCur->idx);
+  if( !pPage->leaf ){
+    pgnoChild = get4byte(pCell);
+  }
+  rc = clearCell(pPage, pCell);
+  if( rc ){
+    return rc;
+  }
+
+  if( !pPage->leaf ){
+    /*
+    ** The entry we are about to delete is not a leaf so if we do not
+    ** do something we will leave a hole on an internal page.
+    ** We have to fill the hole by moving in a cell from a leaf.  The
+    ** next Cell after the one to be deleted is guaranteed to exist and
+    ** to be a leaf so we can use it.
+    */
+    BtCursor leafCur;
+    unsigned char *pNext;
+    int szNext;  /* The compiler warning is wrong: szNext is always 
+                 ** initialized before use.  Adding an extra initialization
+                 ** to silence the compiler slows down the code. */
+    int notUsed;
+    unsigned char *tempCell = 0;
+    assert( !pPage->leafData );
+    sqlite3BtreeGetTempCursor(pCur, &leafCur);
+    rc = sqlite3BtreeNext(&leafCur, &notUsed);
+    if( rc==SQLITE_OK ){
+      rc = sqlite3PagerWrite(leafCur.pPage->pDbPage);
+    }
+    if( rc==SQLITE_OK ){
+      TRACE(("DELETE: table=%d delete internal from %d replace from leaf %d\n",
+         pCur->pgnoRoot, pPage->pgno, leafCur.pPage->pgno));
+      dropCell(pPage, pCur->idx, cellSizePtr(pPage, pCell));
+      pNext = findCell(leafCur.pPage, leafCur.idx);
+      szNext = cellSizePtr(leafCur.pPage, pNext);
+      assert( MX_CELL_SIZE(pBt)>=szNext+4 );
+      tempCell = sqlite3_malloc( MX_CELL_SIZE(pBt) );
+      if( tempCell==0 ){
+        rc = SQLITE_NOMEM;
+      }
+    }
+    if( rc==SQLITE_OK ){
+      rc = insertCell(pPage, pCur->idx, pNext-4, szNext+4, tempCell, 0);
+    }
+    if( rc==SQLITE_OK ){
+      put4byte(findOverflowCell(pPage, pCur->idx), pgnoChild);
+      rc = balance(pPage, 0);
+    }
+    if( rc==SQLITE_OK ){
+      dropCell(leafCur.pPage, leafCur.idx, szNext);
+      rc = balance(leafCur.pPage, 0);
+    }
+    sqlite3_free(tempCell);
+    sqlite3BtreeReleaseTempCursor(&leafCur);
+  }else{
+    TRACE(("DELETE: table=%d delete from leaf %d\n",
+       pCur->pgnoRoot, pPage->pgno));
+    dropCell(pPage, pCur->idx, cellSizePtr(pPage, pCell));
+    rc = balance(pPage, 0);
+  }
+  if( rc==SQLITE_OK ){
+    moveToRoot(pCur);
+  }
+  return rc;
+}
+
+/*
+** Create a new BTree table.  Write into *piTable the page
+** number for the root page of the new table.
+**
+** The type of type is determined by the flags parameter.  Only the
+** following values of flags are currently in use.  Other values for
+** flags might not work:
+**
+**     BTREE_INTKEY|BTREE_LEAFDATA     Used for SQL tables with rowid keys
+**     BTREE_ZERODATA                  Used for SQL indices
+*/
+static int btreeCreateTable(Btree *p, int *piTable, int flags){
+  BtShared *pBt = p->pBt;
+  MemPage *pRoot;
+  Pgno pgnoRoot;
+  int rc;
+
+  assert( sqlite3BtreeHoldsMutex(p) );
+  if( pBt->inTransaction!=TRANS_WRITE ){
+    /* Must start a transaction first */
+    rc = pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+    return rc;
+  }
+  assert( !pBt->readOnly );
+
+#ifdef SQLITE_OMIT_AUTOVACUUM
+  rc = allocateBtreePage(pBt, &pRoot, &pgnoRoot, 1, 0);
+  if( rc ){
+    return rc;
+  }
+#else
+  if( pBt->autoVacuum ){
+    Pgno pgnoMove;      /* Move a page here to make room for the root-page */
+    MemPage *pPageMove; /* The page to move to. */
+
+    /* Creating a new table may probably require moving an existing database
+    ** to make room for the new tables root page. In case this page turns
+    ** out to be an overflow page, delete all overflow page-map caches
+    ** held by open cursors.
+    */
+    invalidateAllOverflowCache(pBt);
+
+    /* Read the value of meta[3] from the database to determine where the
+    ** root page of the new table should go. meta[3] is the largest root-page
+    ** created so far, so the new root-page is (meta[3]+1).
+    */
+    rc = sqlite3BtreeGetMeta(p, 4, &pgnoRoot);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+    pgnoRoot++;
+
+    /* The new root-page may not be allocated on a pointer-map page, or the
+    ** PENDING_BYTE page.
+    */
+    if( pgnoRoot==PTRMAP_PAGENO(pBt, pgnoRoot) ||
+        pgnoRoot==PENDING_BYTE_PAGE(pBt) ){
+      pgnoRoot++;
+    }
+    assert( pgnoRoot>=3 );
+
+    /* Allocate a page. The page that currently resides at pgnoRoot will
+    ** be moved to the allocated page (unless the allocated page happens
+    ** to reside at pgnoRoot).
+    */
+    rc = allocateBtreePage(pBt, &pPageMove, &pgnoMove, pgnoRoot, 1);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+
+    if( pgnoMove!=pgnoRoot ){
+      /* pgnoRoot is the page that will be used for the root-page of
+      ** the new table (assuming an error did not occur). But we were
+      ** allocated pgnoMove. If required (i.e. if it was not allocated
+      ** by extending the file), the current page at position pgnoMove
+      ** is already journaled.
+      */
+      u8 eType;
+      Pgno iPtrPage;
+
+      releasePage(pPageMove);
+
+      /* Move the page currently at pgnoRoot to pgnoMove. */
+      rc = sqlite3BtreeGetPage(pBt, pgnoRoot, &pRoot, 0);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+      rc = ptrmapGet(pBt, pgnoRoot, &eType, &iPtrPage);
+      if( rc!=SQLITE_OK || eType==PTRMAP_ROOTPAGE || eType==PTRMAP_FREEPAGE ){
+        releasePage(pRoot);
+        return rc;
+      }
+      assert( eType!=PTRMAP_ROOTPAGE );
+      assert( eType!=PTRMAP_FREEPAGE );
+      rc = sqlite3PagerWrite(pRoot->pDbPage);
+      if( rc!=SQLITE_OK ){
+        releasePage(pRoot);
+        return rc;
+      }
+      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove);
+      releasePage(pRoot);
+
+      /* Obtain the page at pgnoRoot */
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+      rc = sqlite3BtreeGetPage(pBt, pgnoRoot, &pRoot, 0);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+      rc = sqlite3PagerWrite(pRoot->pDbPage);
+      if( rc!=SQLITE_OK ){
+        releasePage(pRoot);
+        return rc;
+      }
+    }else{
+      pRoot = pPageMove;
+    } 
+
+    /* Update the pointer-map and meta-data with the new root-page number. */
+    rc = ptrmapPut(pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0);
+    if( rc ){
+      releasePage(pRoot);
+      return rc;
+    }
+    rc = sqlite3BtreeUpdateMeta(p, 4, pgnoRoot);
+    if( rc ){
+      releasePage(pRoot);
+      return rc;
+    }
+
+  }else{
+    rc = allocateBtreePage(pBt, &pRoot, &pgnoRoot, 1, 0);
+    if( rc ) return rc;
+  }
+#endif
+  assert( sqlite3PagerIswriteable(pRoot->pDbPage) );
+  zeroPage(pRoot, flags | PTF_LEAF);
+  sqlite3PagerUnref(pRoot->pDbPage);
+  *piTable = (int)pgnoRoot;
+  return SQLITE_OK;
+}
+int sqlite3BtreeCreateTable(Btree *p, int *piTable, int flags){
+  int rc;
+  sqlite3BtreeEnter(p);
+  rc = btreeCreateTable(p, piTable, flags);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Erase the given database page and all its children.  Return
+** the page to the freelist.
+*/
+static int clearDatabasePage(
+  BtShared *pBt,           /* The BTree that contains the table */
+  Pgno pgno,            /* Page number to clear */
+  MemPage *pParent,     /* Parent page.  NULL for the root */
+  int freePageFlag      /* Deallocate page if true */
+){
+  MemPage *pPage = 0;
+  int rc;
+  unsigned char *pCell;
+  int i;
+
+  assert( sqlite3_mutex_held(pBt->mutex) );
+  if( pgno>sqlite3PagerPagecount(pBt->pPager) ){
+    return SQLITE_CORRUPT_BKPT;
+  }
+
+  rc = getAndInitPage(pBt, pgno, &pPage, pParent);
+  if( rc ) goto cleardatabasepage_out;
+  for(i=0; i<pPage->nCell; i++){
+    pCell = findCell(pPage, i);
+    if( !pPage->leaf ){
+      rc = clearDatabasePage(pBt, get4byte(pCell), pPage->pParent, 1);
+      if( rc ) goto cleardatabasepage_out;
+    }
+    rc = clearCell(pPage, pCell);
+    if( rc ) goto cleardatabasepage_out;
+  }
+  if( !pPage->leaf ){
+    rc = clearDatabasePage(pBt, get4byte(&pPage->aData[8]), pPage->pParent, 1);
+    if( rc ) goto cleardatabasepage_out;
+  }
+  if( freePageFlag ){
+    rc = freePage(pPage);
+  }else if( (rc = sqlite3PagerWrite(pPage->pDbPage))==0 ){
+    zeroPage(pPage, pPage->aData[0] | PTF_LEAF);
+  }
+
+cleardatabasepage_out:
+  releasePage(pPage);
+  return rc;
+}
+
+/*
+** Delete all information from a single table in the database.  iTable is
+** the page number of the root of the table.  After this routine returns,
+** the root page is empty, but still exists.
+**
+** This routine will fail with SQLITE_LOCKED if there are any open
+** read cursors on the table.  Open write cursors are moved to the
+** root of the table.
+*/
+int sqlite3BtreeClearTable(Btree *p, int iTable){
+  int rc;
+  BtShared *pBt = p->pBt;
+  sqlite3BtreeEnter(p);
+  if( p->inTrans!=TRANS_WRITE ){
+    rc = pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }else if( (rc = checkReadLocks(p, iTable, 0))!=SQLITE_OK ){
+    /* nothing to do */
+  }else if( SQLITE_OK!=(rc = saveAllCursors(pBt, iTable, 0)) ){
+    /* nothing to do */
+  }else{
+    rc = clearDatabasePage(pBt, (Pgno)iTable, 0, 0);
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Erase all information in a table and add the root of the table to
+** the freelist.  Except, the root of the principle table (the one on
+** page 1) is never added to the freelist.
+**
+** This routine will fail with SQLITE_LOCKED if there are any open
+** cursors on the table.
+**
+** If AUTOVACUUM is enabled and the page at iTable is not the last
+** root page in the database file, then the last root page 
+** in the database file is moved into the slot formerly occupied by
+** iTable and that last slot formerly occupied by the last root page
+** is added to the freelist instead of iTable.  In this say, all
+** root pages are kept at the beginning of the database file, which
+** is necessary for AUTOVACUUM to work right.  *piMoved is set to the 
+** page number that used to be the last root page in the file before
+** the move.  If no page gets moved, *piMoved is set to 0.
+** The last root page is recorded in meta[3] and the value of
+** meta[3] is updated by this procedure.
+*/
+static int btreeDropTable(Btree *p, int iTable, int *piMoved){
+  int rc;
+  MemPage *pPage = 0;
+  BtShared *pBt = p->pBt;
+
+  assert( sqlite3BtreeHoldsMutex(p) );
+  if( p->inTrans!=TRANS_WRITE ){
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+
+  /* It is illegal to drop a table if any cursors are open on the
+  ** database. This is because in auto-vacuum mode the backend may
+  ** need to move another root-page to fill a gap left by the deleted
+  ** root page. If an open cursor was using this page a problem would 
+  ** occur.
+  */
+  if( pBt->pCursor ){
+    return SQLITE_LOCKED;
+  }
+
+  rc = sqlite3BtreeGetPage(pBt, (Pgno)iTable, &pPage, 0);
+  if( rc ) return rc;
+  rc = sqlite3BtreeClearTable(p, iTable);
+  if( rc ){
+    releasePage(pPage);
+    return rc;
+  }
+
+  *piMoved = 0;
+
+  if( iTable>1 ){
+#ifdef SQLITE_OMIT_AUTOVACUUM
+    rc = freePage(pPage);
+    releasePage(pPage);
+#else
+    if( pBt->autoVacuum ){
+      Pgno maxRootPgno;
+      rc = sqlite3BtreeGetMeta(p, 4, &maxRootPgno);
+      if( rc!=SQLITE_OK ){
+        releasePage(pPage);
+        return rc;
+      }
+
+      if( iTable==maxRootPgno ){
+        /* If the table being dropped is the table with the largest root-page
+        ** number in the database, put the root page on the free list. 
+        */
+        rc = freePage(pPage);
+        releasePage(pPage);
+        if( rc!=SQLITE_OK ){
+          return rc;
+        }
+      }else{
+        /* The table being dropped does not have the largest root-page
+        ** number in the database. So move the page that does into the 
+        ** gap left by the deleted root-page.
+        */
+        MemPage *pMove;
+        releasePage(pPage);
+        rc = sqlite3BtreeGetPage(pBt, maxRootPgno, &pMove, 0);
+        if( rc!=SQLITE_OK ){
+          return rc;
+        }
+        rc = relocatePage(pBt, pMove, PTRMAP_ROOTPAGE, 0, iTable);
+        releasePage(pMove);
+        if( rc!=SQLITE_OK ){
+          return rc;
+        }
+        rc = sqlite3BtreeGetPage(pBt, maxRootPgno, &pMove, 0);
+        if( rc!=SQLITE_OK ){
+          return rc;
+        }
+        rc = freePage(pMove);
+        releasePage(pMove);
+        if( rc!=SQLITE_OK ){
+          return rc;
+        }
+        *piMoved = maxRootPgno;
+      }
+
+      /* Set the new 'max-root-page' value in the database header. This
+      ** is the old value less one, less one more if that happens to
+      ** be a root-page number, less one again if that is the
+      ** PENDING_BYTE_PAGE.
+      */
+      maxRootPgno--;
+      if( maxRootPgno==PENDING_BYTE_PAGE(pBt) ){
+        maxRootPgno--;
+      }
+      if( maxRootPgno==PTRMAP_PAGENO(pBt, maxRootPgno) ){
+        maxRootPgno--;
+      }
+      assert( maxRootPgno!=PENDING_BYTE_PAGE(pBt) );
+
+      rc = sqlite3BtreeUpdateMeta(p, 4, maxRootPgno);
+    }else{
+      rc = freePage(pPage);
+      releasePage(pPage);
+    }
+#endif
+  }else{
+    /* If sqlite3BtreeDropTable was called on page 1. */
+    zeroPage(pPage, PTF_INTKEY|PTF_LEAF );
+    releasePage(pPage);
+  }
+  return rc;  
+}
+int sqlite3BtreeDropTable(Btree *p, int iTable, int *piMoved){
+  int rc;
+  sqlite3BtreeEnter(p);
+  rc = btreeDropTable(p, iTable, piMoved);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+
+/*
+** Read the meta-information out of a database file.  Meta[0]
+** is the number of free pages currently in the database.  Meta[1]
+** through meta[15] are available for use by higher layers.  Meta[0]
+** is read-only, the others are read/write.
+** 
+** The schema layer numbers meta values differently.  At the schema
+** layer (and the SetCookie and ReadCookie opcodes) the number of
+** free pages is not visible.  So Cookie[0] is the same as Meta[1].
+*/
+int sqlite3BtreeGetMeta(Btree *p, int idx, u32 *pMeta){
+  DbPage *pDbPage;
+  int rc;
+  unsigned char *pP1;
+  BtShared *pBt = p->pBt;
+
+  sqlite3BtreeEnter(p);
+
+  /* Reading a meta-data value requires a read-lock on page 1 (and hence
+  ** the sqlite_master table. We grab this lock regardless of whether or
+  ** not the SQLITE_ReadUncommitted flag is set (the table rooted at page
+  ** 1 is treated as a special case by queryTableLock() and lockTable()).
+  */
+  rc = queryTableLock(p, 1, READ_LOCK);
+  if( rc!=SQLITE_OK ){
+    sqlite3BtreeLeave(p);
+    return rc;
+  }
+
+  assert( idx>=0 && idx<=15 );
+  rc = sqlite3PagerGet(pBt->pPager, 1, &pDbPage);
+  if( rc ){
+    sqlite3BtreeLeave(p);
+    return rc;
+  }
+  pP1 = (unsigned char *)sqlite3PagerGetData(pDbPage);
+  *pMeta = get4byte(&pP1[36 + idx*4]);
+  sqlite3PagerUnref(pDbPage);
+
+  /* If autovacuumed is disabled in this build but we are trying to 
+  ** access an autovacuumed database, then make the database readonly. 
+  */
+#ifdef SQLITE_OMIT_AUTOVACUUM
+  if( idx==4 && *pMeta>0 ) pBt->readOnly = 1;
+#endif
+
+  /* Grab the read-lock on page 1. */
+  rc = lockTable(p, 1, READ_LOCK);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Write meta-information back into the database.  Meta[0] is
+** read-only and may not be written.
+*/
+int sqlite3BtreeUpdateMeta(Btree *p, int idx, u32 iMeta){
+  BtShared *pBt = p->pBt;
+  unsigned char *pP1;
+  int rc;
+  assert( idx>=1 && idx<=15 );
+  sqlite3BtreeEnter(p);
+  if( p->inTrans!=TRANS_WRITE ){
+    rc = pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }else{
+    assert( pBt->pPage1!=0 );
+    pP1 = pBt->pPage1->aData;
+    rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
+    if( rc==SQLITE_OK ){
+      put4byte(&pP1[36 + idx*4], iMeta);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      if( idx==7 ){
+        assert( pBt->autoVacuum || iMeta==0 );
+        assert( iMeta==0 || iMeta==1 );
+        pBt->incrVacuum = iMeta;
+      }
+#endif
+    }
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+/*
+** Return the flag byte at the beginning of the page that the cursor
+** is currently pointing to.
+*/
+int sqlite3BtreeFlags(BtCursor *pCur){
+  /* TODO: What about CURSOR_REQUIRESEEK state? Probably need to call
+  ** restoreOrClearCursorPosition() here.
+  */
+  MemPage *pPage = pCur->pPage;
+  assert( cursorHoldsMutex(pCur) );
+  assert( pPage->pBt==pCur->pBt );
+  return pPage ? pPage->aData[pPage->hdrOffset] : 0;
+}
+
+
+/*
+** Return the pager associated with a BTree.  This routine is used for
+** testing and debugging only.
+*/
+Pager *sqlite3BtreePager(Btree *p){
+  return p->pBt->pPager;
+}
+
+#ifndef SQLITE_OMIT_INTEGRITY_CHECK
+/*
+** Append a message to the error message string.
+*/
+static void checkAppendMsg(
+  IntegrityCk *pCheck,
+  char *zMsg1,
+  const char *zFormat,
+  ...
+){
+  va_list ap;
+  char *zMsg2;
+  if( !pCheck->mxErr ) return;
+  pCheck->mxErr--;
+  pCheck->nErr++;
+  va_start(ap, zFormat);
+  zMsg2 = sqlite3VMPrintf(0, zFormat, ap);
+  va_end(ap);
+  if( zMsg1==0 ) zMsg1 = "";
+  if( pCheck->zErrMsg ){
+    char *zOld = pCheck->zErrMsg;
+    pCheck->zErrMsg = 0;
+    sqlite3SetString(&pCheck->zErrMsg, zOld, "\n", zMsg1, zMsg2, (char*)0);
+    sqlite3_free(zOld);
+  }else{
+    sqlite3SetString(&pCheck->zErrMsg, zMsg1, zMsg2, (char*)0);
+  }
+  sqlite3_free(zMsg2);
+}
+#endif /* SQLITE_OMIT_INTEGRITY_CHECK */
+
+#ifndef SQLITE_OMIT_INTEGRITY_CHECK
+/*
+** Add 1 to the reference count for page iPage.  If this is the second
+** reference to the page, add an error message to pCheck->zErrMsg.
+** Return 1 if there are 2 ore more references to the page and 0 if
+** if this is the first reference to the page.
+**
+** Also check that the page number is in bounds.
+*/
+static int checkRef(IntegrityCk *pCheck, int iPage, char *zContext){
+  if( iPage==0 ) return 1;
+  if( iPage>pCheck->nPage || iPage<0 ){
+    checkAppendMsg(pCheck, zContext, "invalid page number %d", iPage);
+    return 1;
+  }
+  if( pCheck->anRef[iPage]==1 ){
+    checkAppendMsg(pCheck, zContext, "2nd reference to page %d", iPage);
+    return 1;
+  }
+  return  (pCheck->anRef[iPage]++)>1;
+}
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+/*
+** Check that the entry in the pointer-map for page iChild maps to 
+** page iParent, pointer type ptrType. If not, append an error message
+** to pCheck.
+*/
+static void checkPtrmap(
+  IntegrityCk *pCheck,   /* Integrity check context */
+  Pgno iChild,           /* Child page number */
+  u8 eType,              /* Expected pointer map type */
+  Pgno iParent,          /* Expected pointer map parent page number */
+  char *zContext         /* Context description (used for error msg) */
+){
+  int rc;
+  u8 ePtrmapType;
+  Pgno iPtrmapParent;
+
+  rc = ptrmapGet(pCheck->pBt, iChild, &ePtrmapType, &iPtrmapParent);
+  if( rc!=SQLITE_OK ){
+    checkAppendMsg(pCheck, zContext, "Failed to read ptrmap key=%d", iChild);
+    return;
+  }
+
+  if( ePtrmapType!=eType || iPtrmapParent!=iParent ){
+    checkAppendMsg(pCheck, zContext, 
+      "Bad ptr map entry key=%d expected=(%d,%d) got=(%d,%d)", 
+      iChild, eType, iParent, ePtrmapType, iPtrmapParent);
+  }
+}
+#endif
+
+/*
+** Check the integrity of the freelist or of an overflow page list.
+** Verify that the number of pages on the list is N.
+*/
+static void checkList(
+  IntegrityCk *pCheck,  /* Integrity checking context */
+  int isFreeList,       /* True for a freelist.  False for overflow page list */
+  int iPage,            /* Page number for first page in the list */
+  int N,                /* Expected number of pages in the list */
+  char *zContext        /* Context for error messages */
+){
+  int i;
+  int expected = N;
+  int iFirst = iPage;
+  while( N-- > 0 && pCheck->mxErr ){
+    DbPage *pOvflPage;
+    unsigned char *pOvflData;
+    if( iPage<1 ){
+      checkAppendMsg(pCheck, zContext,
+         "%d of %d pages missing from overflow list starting at %d",
+          N+1, expected, iFirst);
+      break;
+    }
+    if( checkRef(pCheck, iPage, zContext) ) break;
+    if( sqlite3PagerGet(pCheck->pPager, (Pgno)iPage, &pOvflPage) ){
+      checkAppendMsg(pCheck, zContext, "failed to get page %d", iPage);
+      break;
+    }
+    pOvflData = (unsigned char *)sqlite3PagerGetData(pOvflPage);
+    if( isFreeList ){
+      int n = get4byte(&pOvflData[4]);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      if( pCheck->pBt->autoVacuum ){
+        checkPtrmap(pCheck, iPage, PTRMAP_FREEPAGE, 0, zContext);
+      }
+#endif
+      if( n>pCheck->pBt->usableSize/4-8 ){
+        checkAppendMsg(pCheck, zContext,
+           "freelist leaf count too big on page %d", iPage);
+        N--;
+      }else{
+        for(i=0; i<n; i++){
+          Pgno iFreePage = get4byte(&pOvflData[8+i*4]);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+          if( pCheck->pBt->autoVacuum ){
+            checkPtrmap(pCheck, iFreePage, PTRMAP_FREEPAGE, 0, zContext);
+          }
+#endif
+          checkRef(pCheck, iFreePage, zContext);
+        }
+        N -= n;
+      }
+    }
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    else{
+      /* If this database supports auto-vacuum and iPage is not the last
+      ** page in this overflow list, check that the pointer-map entry for
+      ** the following page matches iPage.
+      */
+      if( pCheck->pBt->autoVacuum && N>0 ){
+        i = get4byte(pOvflData);
+        checkPtrmap(pCheck, i, PTRMAP_OVERFLOW2, iPage, zContext);
+      }
+    }
+#endif
+    iPage = get4byte(pOvflData);
+    sqlite3PagerUnref(pOvflPage);
+  }
+}
+#endif /* SQLITE_OMIT_INTEGRITY_CHECK */
+
+#ifndef SQLITE_OMIT_INTEGRITY_CHECK
+/*
+** Do various sanity checks on a single page of a tree.  Return
+** the tree depth.  Root pages return 0.  Parents of root pages
+** return 1, and so forth.
+** 
+** These checks are done:
+**
+**      1.  Make sure that cells and freeblocks do not overlap
+**          but combine to completely cover the page.
+**  NO  2.  Make sure cell keys are in order.
+**  NO  3.  Make sure no key is less than or equal to zLowerBound.
+**  NO  4.  Make sure no key is greater than or equal to zUpperBound.
+**      5.  Check the integrity of overflow pages.
+**      6.  Recursively call checkTreePage on all children.
+**      7.  Verify that the depth of all children is the same.
+**      8.  Make sure this page is at least 33% full or else it is
+**          the root of the tree.
+*/
+static int checkTreePage(
+  IntegrityCk *pCheck,  /* Context for the sanity check */
+  int iPage,            /* Page number of the page to check */
+  MemPage *pParent,     /* Parent page */
+  char *zParentContext  /* Parent context */
+){
+  MemPage *pPage;
+  int i, rc, depth, d2, pgno, cnt;
+  int hdr, cellStart;
+  int nCell;
+  u8 *data;
+  BtShared *pBt;
+  int usableSize;
+  char zContext[100];
+  char *hit;
+
+  sqlite3_snprintf(sizeof(zContext), zContext, "Page %d: ", iPage);
+
+  /* Check that the page exists
+  */
+  pBt = pCheck->pBt;
+  usableSize = pBt->usableSize;
+  if( iPage==0 ) return 0;
+  if( checkRef(pCheck, iPage, zParentContext) ) return 0;
+  if( (rc = sqlite3BtreeGetPage(pBt, (Pgno)iPage, &pPage, 0))!=0 ){
+    checkAppendMsg(pCheck, zContext,
+       "unable to get the page. error code=%d", rc);
+    return 0;
+  }
+  if( (rc = sqlite3BtreeInitPage(pPage, pParent))!=0 ){
+    checkAppendMsg(pCheck, zContext, 
+                   "sqlite3BtreeInitPage() returns error code %d", rc);
+    releasePage(pPage);
+    return 0;
+  }
+
+  /* Check out all the cells.
+  */
+  depth = 0;
+  for(i=0; i<pPage->nCell && pCheck->mxErr; i++){
+    u8 *pCell;
+    int sz;
+    CellInfo info;
+
+    /* Check payload overflow pages
+    */
+    sqlite3_snprintf(sizeof(zContext), zContext,
+             "On tree page %d cell %d: ", iPage, i);
+    pCell = findCell(pPage,i);
+    sqlite3BtreeParseCellPtr(pPage, pCell, &info);
+    sz = info.nData;
+    if( !pPage->intKey ) sz += info.nKey;
+    assert( sz==info.nPayload );
+    if( sz>info.nLocal ){
+      int nPage = (sz - info.nLocal + usableSize - 5)/(usableSize - 4);
+      Pgno pgnoOvfl = get4byte(&pCell[info.iOverflow]);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      if( pBt->autoVacuum ){
+        checkPtrmap(pCheck, pgnoOvfl, PTRMAP_OVERFLOW1, iPage, zContext);
+      }
+#endif
+      checkList(pCheck, 0, pgnoOvfl, nPage, zContext);
+    }
+
+    /* Check sanity of left child page.
+    */
+    if( !pPage->leaf ){
+      pgno = get4byte(pCell);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+      if( pBt->autoVacuum ){
+        checkPtrmap(pCheck, pgno, PTRMAP_BTREE, iPage, zContext);
+      }
+#endif
+      d2 = checkTreePage(pCheck,pgno,pPage,zContext);
+      if( i>0 && d2!=depth ){
+        checkAppendMsg(pCheck, zContext, "Child page depth differs");
+      }
+      depth = d2;
+    }
+  }
+  if( !pPage->leaf ){
+    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
+    sqlite3_snprintf(sizeof(zContext), zContext, 
+                     "On page %d at right child: ", iPage);
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( pBt->autoVacuum ){
+      checkPtrmap(pCheck, pgno, PTRMAP_BTREE, iPage, 0);
+    }
+#endif
+    checkTreePage(pCheck, pgno, pPage, zContext);
+  }
+ 
+  /* Check for complete coverage of the page
+  */
+  data = pPage->aData;
+  hdr = pPage->hdrOffset;
+  hit = sqlite3MallocZero( usableSize );
+  if( hit ){
+    memset(hit, 1, get2byte(&data[hdr+5]));
+    nCell = get2byte(&data[hdr+3]);
+    cellStart = hdr + 12 - 4*pPage->leaf;
+    for(i=0; i<nCell; i++){
+      int pc = get2byte(&data[cellStart+i*2]);
+      int size = cellSizePtr(pPage, &data[pc]);
+      int j;
+      if( (pc+size-1)>=usableSize || pc<0 ){
+        checkAppendMsg(pCheck, 0, 
+            "Corruption detected in cell %d on page %d",i,iPage,0);
+      }else{
+        for(j=pc+size-1; j>=pc; j--) hit[j]++;
+      }
+    }
+    for(cnt=0, i=get2byte(&data[hdr+1]); i>0 && i<usableSize && cnt<10000; 
+           cnt++){
+      int size = get2byte(&data[i+2]);
+      int j;
+      if( (i+size-1)>=usableSize || i<0 ){
+        checkAppendMsg(pCheck, 0,  
+            "Corruption detected in cell %d on page %d",i,iPage,0);
+      }else{
+        for(j=i+size-1; j>=i; j--) hit[j]++;
+      }
+      i = get2byte(&data[i]);
+    }
+    for(i=cnt=0; i<usableSize; i++){
+      if( hit[i]==0 ){
+        cnt++;
+      }else if( hit[i]>1 ){
+        checkAppendMsg(pCheck, 0,
+          "Multiple uses for byte %d of page %d", i, iPage);
+        break;
+      }
+    }
+    if( cnt!=data[hdr+7] ){
+      checkAppendMsg(pCheck, 0, 
+          "Fragmented space is %d byte reported as %d on page %d",
+          cnt, data[hdr+7], iPage);
+    }
+  }
+  sqlite3_free(hit);
+
+  releasePage(pPage);
+  return depth+1;
+}
+#endif /* SQLITE_OMIT_INTEGRITY_CHECK */
+
+#ifndef SQLITE_OMIT_INTEGRITY_CHECK
+/*
+** This routine does a complete check of the given BTree file.  aRoot[] is
+** an array of pages numbers were each page number is the root page of
+** a table.  nRoot is the number of entries in aRoot.
+**
+** If everything checks out, this routine returns NULL.  If something is
+** amiss, an error message is written into memory obtained from malloc()
+** and a pointer to that error message is returned.  The calling function
+** is responsible for freeing the error message when it is done.
+*/
+char *sqlite3BtreeIntegrityCheck(
+  Btree *p,     /* The btree to be checked */
+  int *aRoot,   /* An array of root pages numbers for individual trees */
+  int nRoot,    /* Number of entries in aRoot[] */
+  int mxErr,    /* Stop reporting errors after this many */
+  int *pnErr    /* Write number of errors seen to this variable */
+){
+  int i;
+  int nRef;
+  IntegrityCk sCheck;
+  BtShared *pBt = p->pBt;
+
+  sqlite3BtreeEnter(p);
+  nRef = sqlite3PagerRefcount(pBt->pPager);
+  if( lockBtreeWithRetry(p)!=SQLITE_OK ){
+    sqlite3BtreeLeave(p);
+    return sqlite3StrDup("Unable to acquire a read lock on the database");
+  }
+  sCheck.pBt = pBt;
+  sCheck.pPager = pBt->pPager;
+  sCheck.nPage = sqlite3PagerPagecount(sCheck.pPager);
+  sCheck.mxErr = mxErr;
+  sCheck.nErr = 0;
+  *pnErr = 0;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  if( pBt->nTrunc!=0 ){
+    sCheck.nPage = pBt->nTrunc;
+  }
+#endif
+  if( sCheck.nPage==0 ){
+    unlockBtreeIfUnused(pBt);
+    sqlite3BtreeLeave(p);
+    return 0;
+  }
+  sCheck.anRef = sqlite3_malloc( (sCheck.nPage+1)*sizeof(sCheck.anRef[0]) );
+  if( !sCheck.anRef ){
+    unlockBtreeIfUnused(pBt);
+    *pnErr = 1;
+    sqlite3BtreeLeave(p);
+    return sqlite3MPrintf(p->pSqlite, "Unable to malloc %d bytes", 
+        (sCheck.nPage+1)*sizeof(sCheck.anRef[0]));
+  }
+  for(i=0; i<=sCheck.nPage; i++){ sCheck.anRef[i] = 0; }
+  i = PENDING_BYTE_PAGE(pBt);
+  if( i<=sCheck.nPage ){
+    sCheck.anRef[i] = 1;
+  }
+  sCheck.zErrMsg = 0;
+
+  /* Check the integrity of the freelist
+  */
+  checkList(&sCheck, 1, get4byte(&pBt->pPage1->aData[32]),
+            get4byte(&pBt->pPage1->aData[36]), "Main freelist: ");
+
+  /* Check all the tables.
+  */
+  for(i=0; i<nRoot && sCheck.mxErr; i++){
+    if( aRoot[i]==0 ) continue;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( pBt->autoVacuum && aRoot[i]>1 ){
+      checkPtrmap(&sCheck, aRoot[i], PTRMAP_ROOTPAGE, 0, 0);
+    }
+#endif
+    checkTreePage(&sCheck, aRoot[i], 0, "List of tree roots: ");
+  }
+
+  /* Make sure every page in the file is referenced
+  */
+  for(i=1; i<=sCheck.nPage && sCheck.mxErr; i++){
+#ifdef SQLITE_OMIT_AUTOVACUUM
+    if( sCheck.anRef[i]==0 ){
+      checkAppendMsg(&sCheck, 0, "Page %d is never used", i);
+    }
+#else
+    /* If the database supports auto-vacuum, make sure no tables contain
+    ** references to pointer-map pages.
+    */
+    if( sCheck.anRef[i]==0 && 
+       (PTRMAP_PAGENO(pBt, i)!=i || !pBt->autoVacuum) ){
+      checkAppendMsg(&sCheck, 0, "Page %d is never used", i);
+    }
+    if( sCheck.anRef[i]!=0 && 
+       (PTRMAP_PAGENO(pBt, i)==i && pBt->autoVacuum) ){
+      checkAppendMsg(&sCheck, 0, "Pointer map page %d is referenced", i);
+    }
+#endif
+  }
+
+  /* Make sure this analysis did not leave any unref() pages
+  */
+  unlockBtreeIfUnused(pBt);
+  if( nRef != sqlite3PagerRefcount(pBt->pPager) ){
+    checkAppendMsg(&sCheck, 0, 
+      "Outstanding page count goes from %d to %d during this analysis",
+      nRef, sqlite3PagerRefcount(pBt->pPager)
+    );
+  }
+
+  /* Clean  up and report errors.
+  */
+  sqlite3BtreeLeave(p);
+  sqlite3_free(sCheck.anRef);
+  *pnErr = sCheck.nErr;
+  return sCheck.zErrMsg;
+}
+#endif /* SQLITE_OMIT_INTEGRITY_CHECK */
+
+/*
+** Return the full pathname of the underlying database file.
+**
+** The pager filename is invariant as long as the pager is
+** open so it is safe to access without the BtShared mutex.
+*/
+const char *sqlite3BtreeGetFilename(Btree *p){
+  assert( p->pBt->pPager!=0 );
+  return sqlite3PagerFilename(p->pBt->pPager);
+}
+
+/*
+** Return the pathname of the directory that contains the database file.
+**
+** The pager directory name is invariant as long as the pager is
+** open so it is safe to access without the BtShared mutex.
+*/
+const char *sqlite3BtreeGetDirname(Btree *p){
+  assert( p->pBt->pPager!=0 );
+  return sqlite3PagerDirname(p->pBt->pPager);
+}
+
+/*
+** Return the pathname of the journal file for this database. The return
+** value of this routine is the same regardless of whether the journal file
+** has been created or not.
+**
+** The pager journal filename is invariant as long as the pager is
+** open so it is safe to access without the BtShared mutex.
+*/
+const char *sqlite3BtreeGetJournalname(Btree *p){
+  assert( p->pBt->pPager!=0 );
+  return sqlite3PagerJournalname(p->pBt->pPager);
+}
+
+#ifndef SQLITE_OMIT_VACUUM
+/*
+** Copy the complete content of pBtFrom into pBtTo.  A transaction
+** must be active for both files.
+**
+** The size of file pBtFrom may be reduced by this operation.
+** If anything goes wrong, the transaction on pBtFrom is rolled back.
+*/
+static int btreeCopyFile(Btree *pTo, Btree *pFrom){
+  int rc = SQLITE_OK;
+  Pgno i, nPage, nToPage, iSkip;
+
+  BtShared *pBtTo = pTo->pBt;
+  BtShared *pBtFrom = pFrom->pBt;
+
+  if( pTo->inTrans!=TRANS_WRITE || pFrom->inTrans!=TRANS_WRITE ){
+    return SQLITE_ERROR;
+  }
+  if( pBtTo->pCursor ) return SQLITE_BUSY;
+  nToPage = sqlite3PagerPagecount(pBtTo->pPager);
+  nPage = sqlite3PagerPagecount(pBtFrom->pPager);
+  iSkip = PENDING_BYTE_PAGE(pBtTo);
+  for(i=1; rc==SQLITE_OK && i<=nPage; i++){
+    DbPage *pDbPage;
+    if( i==iSkip ) continue;
+    rc = sqlite3PagerGet(pBtFrom->pPager, i, &pDbPage);
+    if( rc ) break;
+    rc = sqlite3PagerOverwrite(pBtTo->pPager, i, sqlite3PagerGetData(pDbPage));
+    sqlite3PagerUnref(pDbPage);
+  }
+
+  /* If the file is shrinking, journal the pages that are being truncated
+  ** so that they can be rolled back if the commit fails.
+  */
+  for(i=nPage+1; rc==SQLITE_OK && i<=nToPage; i++){
+    DbPage *pDbPage;
+    if( i==iSkip ) continue;
+    rc = sqlite3PagerGet(pBtTo->pPager, i, &pDbPage);
+    if( rc ) break;
+    rc = sqlite3PagerWrite(pDbPage);
+    sqlite3PagerDontWrite(pDbPage);
+    /* Yeah.  It seems wierd to call DontWrite() right after Write().  But
+    ** that is because the names of those procedures do not exactly 
+    ** represent what they do.  Write() really means "put this page in the
+    ** rollback journal and mark it as dirty so that it will be written
+    ** to the database file later."  DontWrite() undoes the second part of
+    ** that and prevents the page from being written to the database.  The
+    ** page is still on the rollback journal, though.  And that is the whole
+    ** point of this loop: to put pages on the rollback journal. */
+    sqlite3PagerUnref(pDbPage);
+  }
+  if( !rc && nPage<nToPage ){
+    rc = sqlite3PagerTruncate(pBtTo->pPager, nPage);
+  }
+
+  if( rc ){
+    sqlite3BtreeRollback(pTo);
+  }
+  return rc;  
+}
+int sqlite3BtreeCopyFile(Btree *pTo, Btree *pFrom){
+  int rc;
+  sqlite3BtreeEnter(pTo);
+  sqlite3BtreeEnter(pFrom);
+  rc = btreeCopyFile(pTo, pFrom);
+  sqlite3BtreeLeave(pFrom);
+  sqlite3BtreeLeave(pTo);
+  return rc;
+}
+
+#endif /* SQLITE_OMIT_VACUUM */
+
+/*
+** Return non-zero if a transaction is active.
+*/
+int sqlite3BtreeIsInTrans(Btree *p){
+  assert( p==0 || sqlite3_mutex_held(p->pSqlite->mutex) );
+  return (p && (p->inTrans==TRANS_WRITE));
+}
+
+/*
+** Return non-zero if a statement transaction is active.
+*/
+int sqlite3BtreeIsInStmt(Btree *p){
+  assert( sqlite3BtreeHoldsMutex(p) );
+  return (p->pBt && p->pBt->inStmt);
+}
+
+/*
+** Return non-zero if a read (or write) transaction is active.
+*/
+int sqlite3BtreeIsInReadTrans(Btree *p){
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );
+  return (p && (p->inTrans!=TRANS_NONE));
+}
+
+/*
+** This function returns a pointer to a blob of memory associated with
+** a single shared-btree. The memory is used by client code for it's own
+** purposes (for example, to store a high-level schema associated with 
+** the shared-btree). The btree layer manages reference counting issues.
+**
+** The first time this is called on a shared-btree, nBytes bytes of memory
+** are allocated, zeroed, and returned to the caller. For each subsequent 
+** call the nBytes parameter is ignored and a pointer to the same blob
+** of memory returned. 
+**
+** Just before the shared-btree is closed, the function passed as the 
+** xFree argument when the memory allocation was made is invoked on the 
+** blob of allocated memory. This function should not call sqlite3_free()
+** on the memory, the btree layer does that.
+*/
+void *sqlite3BtreeSchema(Btree *p, int nBytes, void(*xFree)(void *)){
+  BtShared *pBt = p->pBt;
+  sqlite3BtreeEnter(p);
+  if( !pBt->pSchema ){
+    pBt->pSchema = sqlite3MallocZero(nBytes);
+    pBt->xFreeSchema = xFree;
+  }
+  sqlite3BtreeLeave(p);
+  return pBt->pSchema;
+}
+
+/*
+** Return true if another user of the same shared btree as the argument
+** handle holds an exclusive lock on the sqlite_master table.
+*/
+int sqlite3BtreeSchemaLocked(Btree *p){
+  int rc;
+  assert( sqlite3_mutex_held(p->pSqlite->mutex) );
+  sqlite3BtreeEnter(p);
+  rc = (queryTableLock(p, MASTER_ROOT, READ_LOCK)!=SQLITE_OK);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
+
+#ifndef SQLITE_OMIT_SHARED_CACHE
+/*
+** Obtain a lock on the table whose root page is iTab.  The
+** lock is a write lock if isWritelock is true or a read lock
+** if it is false.
+*/
+int sqlite3BtreeLockTable(Btree *p, int iTab, u8 isWriteLock){
+  int rc = SQLITE_OK;
+  u8 lockType = (isWriteLock?WRITE_LOCK:READ_LOCK);
+  sqlite3BtreeEnter(p);
+  rc = queryTableLock(p, iTab, lockType);
+  if( rc==SQLITE_OK ){
+    rc = lockTable(p, iTab, lockType);
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+#endif
+
+#ifndef SQLITE_OMIT_INCRBLOB
+/*
+** Argument pCsr must be a cursor opened for writing on an 
+** INTKEY table currently pointing at a valid table entry. 
+** This function modifies the data stored as part of that entry.
+** Only the data content may only be modified, it is not possible
+** to change the length of the data stored.
+*/
+int sqlite3BtreePutData(BtCursor *pCsr, u32 offset, u32 amt, void *z){
+  assert( cursorHoldsMutex(pCsr) );
+  assert( sqlite3_mutex_held(pCsr->pBtree->pSqlite->mutex) );
+  assert(pCsr->isIncrblobHandle);
+  if( pCsr->eState>=CURSOR_REQUIRESEEK ){
+    if( pCsr->eState==CURSOR_FAULT ){
+      return pCsr->skip;
+    }else{
+      return SQLITE_ABORT;
+    }
+  }
+
+  /* Check some preconditions: 
+  **   (a) the cursor is open for writing,
+  **   (b) there is no read-lock on the table being modified and
+  **   (c) the cursor points at a valid row of an intKey table.
+  */
+  if( !pCsr->wrFlag ){
+    return SQLITE_READONLY;
+  }
+  assert( !pCsr->pBt->readOnly 
+          && pCsr->pBt->inTransaction==TRANS_WRITE );
+  if( checkReadLocks(pCsr->pBtree, pCsr->pgnoRoot, pCsr) ){
+    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
+  }
+  if( pCsr->eState==CURSOR_INVALID || !pCsr->pPage->intKey ){
+    return SQLITE_ERROR;
+  }
+
+  return accessPayload(pCsr, offset, amt, (unsigned char *)z, 0, 1);
+}
+
+/* 
+** Set a flag on this cursor to cache the locations of pages from the 
+** overflow list for the current row. This is used by cursors opened
+** for incremental blob IO only.
+**
+** This function sets a flag only. The actual page location cache
+** (stored in BtCursor.aOverflow[]) is allocated and used by function
+** accessPayload() (the worker function for sqlite3BtreeData() and
+** sqlite3BtreePutData()).
+*/
+void sqlite3BtreeCacheOverflow(BtCursor *pCur){
+  assert( cursorHoldsMutex(pCur) );
+  assert( sqlite3_mutex_held(pCur->pBtree->pSqlite->mutex) );
+  assert(!pCur->isIncrblobHandle);
+  assert(!pCur->aOverflow);
+  pCur->isIncrblobHandle = 1;
+}
+#endif