Test conversion to TQt3 from Qt3 8c6fc1f8e35fd264dd01c582ca5e7549b32ab731

1 files changed, 3579 insertions, 0 deletions

diff --git a/src/3rdparty/sqlite/btree.c b/src/3rdparty/sqlite/btree.c
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+++ b/src/3rdparty/sqlite/btree.c
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+/*
+** 2001 September 15
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+** $Id: btree.c,v 1.102 2004/02/14 17:35:07 drh Exp $
+**
+** This file implements a external (disk-based) database using BTrees.
+** For a detailed discussion of BTrees, refer to
+**
+**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
+**     "Sorting And Searching", pages 473-480. Addison-Wesley
+**     Publishing Company, Reading, Massachusetts.
+**
+** The basic idea is that each page of the file contains N database
+** entries and N+1 pointers to subpages.
+**
+**   ----------------------------------------------------------------
+**   |  Ptr(0) | Key(0) | Ptr(1) | Key(1) | ... | Key(N) | Ptr(N+1) |
+**   ----------------------------------------------------------------
+**
+** All of the keys on the page that Ptr(0) points to have values less
+** than Key(0).  All of the keys on page Ptr(1) and its subpages have
+** values greater than Key(0) and less than Key(1).  All of the keys
+** on Ptr(N+1) and its subpages have values greater than Key(N).  And
+** so forth.
+**
+** Finding a particular key retquires reading O(log(M)) pages from the 
+** disk where M is the number of entries in the tree.
+**
+** In this implementation, a single file can hold one or more separate 
+** BTrees.  Each BTree is identified by the index of its root page.  The
+** key and data for any entry are combined to form the "payload".  Up to
+** MX_LOCAL_PAYLOAD bytes of payload can be carried directly on the
+** database page.  If the payload is larger than MX_LOCAL_PAYLOAD bytes
+** then surplus bytes are stored on overflow pages.  The payload for an
+** entry and the preceding pointer are combined to form a "Cell".  Each 
+** page has a small header which contains the Ptr(N+1) pointer.
+**
+** The first page of the file contains a magic string used to verify that
+** the file really is a valid BTree database, a pointer to a list of unused
+** pages in the file, and some meta information.  The root of the first
+** BTree begins on page 2 of the file.  (Pages are numbered beginning with
+** 1, not 0.)  Thus a minimum database contains 2 pages.
+*/
+#include "sqliteInt.h"
+#include "pager.h"
+#include "btree.h"
+#include <assert.h>
+
+/* Forward declarations */
+static BtOps sqliteBtreeOps;
+static BtCursorOps sqliteBtreeCursorOps;
+
+/*
+** Macros used for byteswapping.  B is a pointer to the Btree
+** structure.  This is needed to access the Btree.needSwab boolean
+** in order to tell if byte swapping is needed or not.
+** X is an unsigned integer.  SWAB16 byte swaps a 16-bit integer.
+** SWAB32 byteswaps a 32-bit integer.
+*/
+#define SWAB16(B,X)   ((B)->needSwab? swab16((u16)X) : ((u16)X))
+#define SWAB32(B,X)   ((B)->needSwab? swab32(X) : (X))
+#define SWAB_ADD(B,X,A) \
+   if((B)->needSwab){ X=swab32(swab32(X)+A); }else{ X += (A); }
+
+/*
+** The following global variable - available only if SQLITE_TEST is
+** defined - is used to determine whether new databases are created in
+** native byte order or in non-native byte order.  Non-native byte order
+** databases are created for testing purposes only.  Under normal operation,
+** only native byte-order databases should be created, but we should be
+** able to read or write existing databases regardless of the byteorder.
+*/
+#ifdef SQLITE_TEST
+int btree_native_byte_order = 1;
+#else
+# define btree_native_byte_order 1
+#endif
+
+/*
+** Forward declarations of structures used only in this file.
+*/
+typedef struct PageOne PageOne;
+typedef struct MemPage MemPage;
+typedef struct PageHdr PageHdr;
+typedef struct Cell Cell;
+typedef struct CellHdr CellHdr;
+typedef struct FreeBlk FreeBlk;
+typedef struct OverflowPage OverflowPage;
+typedef struct FreelistInfo FreelistInfo;
+
+/*
+** All structures on a database page are aligned to 4-byte boundries.
+** This routine rounds up a number of bytes to the next multiple of 4.
+**
+** This might need to change for computer architectures that retquire
+** and 8-byte alignment boundry for structures.
+*/
+#define ROUNDUP(X)  ((X+3) & ~3)
+
+/*
+** This is a magic string that appears at the beginning of every
+** SQLite database in order to identify the file as a real database.
+*/
+static const char zMagicHeader[] = 
+   "** This file contains an SQLite 2.1 database **";
+#define MAGIC_SIZE (sizeof(zMagicHeader))
+
+/*
+** This is a magic integer also used to test the integrity of the database
+** file.  This integer is used in addition to the string above so that
+** if the file is written on a little-endian architecture and read
+** on a big-endian architectures (or vice versa) we can detect the
+** problem.
+**
+** The number used was obtained at random and has no special
+** significance other than the fact that it represents a different
+** integer on little-endian and big-endian machines.
+*/
+#define MAGIC 0xdae37528
+
+/*
+** The first page of the database file contains a magic header string
+** to identify the file as an SQLite database file.  It also contains
+** a pointer to the first free page of the file.  Page 2 contains the
+** root of the principle BTree.  The file might contain other BTrees
+** rooted on pages above 2.
+**
+** The first page also contains SQLITE_N_BTREE_META integers that
+** can be used by higher-level routines.
+**
+** Remember that pages are numbered beginning with 1.  (See pager.c
+** for additional information.)  Page 0 does not exist and a page
+** number of 0 is used to mean "no such page".
+*/
+struct PageOne {
+  char zMagic[MAGIC_SIZE]; /* String that identifies the file as a database */
+  int iMagic;              /* Integer to verify correct byte order */
+  Pgno freeList;           /* First free page in a list of all free pages */
+  int nFree;               /* Number of pages on the free list */
+  int aMeta[SQLITE_N_BTREE_META-1];  /* User defined integers */
+};
+
+/*
+** Each database page has a header that is an instance of this
+** structure.
+**
+** PageHdr.firstFree is 0 if there is no free space on this page.
+** Otherwise, PageHdr.firstFree is the index in MemPage.u.aDisk[] of a 
+** FreeBlk structure that describes the first block of free space.  
+** All free space is defined by a linked list of FreeBlk structures.
+**
+** Data is stored in a linked list of Cell structures.  PageHdr.firstCell
+** is the index into MemPage.u.aDisk[] of the first cell on the page.  The
+** Cells are kept in sorted order.
+**
+** A Cell contains all information about a database entry and a pointer
+** to a child page that contains other entries less than itself.  In
+** other words, the i-th Cell contains both Ptr(i) and Key(i).  The
+** right-most pointer of the page is contained in PageHdr.rightChild.
+*/
+struct PageHdr {
+  Pgno rightChild;  /* Child page that comes after all cells on this page */
+  u16 firstCell;    /* Index in MemPage.u.aDisk[] of the first cell */
+  u16 firstFree;    /* Index in MemPage.u.aDisk[] of the first free block */
+};
+
+/*
+** Entries on a page of the database are called "Cells".  Each Cell
+** has a header and data.  This structure defines the header.  The
+** key and data (collectively the "payload") follow this header on
+** the database page.
+**
+** A definition of the complete Cell structure is given below.  The
+** header for the cell must be defined first in order to do some
+** of the sizing #defines that follow.
+*/
+struct CellHdr {
+  Pgno leftChild; /* Child page that comes before this cell */
+  u16 nKey;       /* Number of bytes in the key */
+  u16 iNext;      /* Index in MemPage.u.aDisk[] of next cell in sorted order */
+  u8 nKeyHi;      /* Upper 8 bits of key size for keys larger than 64K bytes */
+  u8 nDataHi;     /* Upper 8 bits of data size when the size is more than 64K */
+  u16 nData;      /* Number of bytes of data */
+};
+
+/*
+** The key and data size are split into a lower 16-bit segment and an
+** upper 8-bit segment in order to pack them together into a smaller
+** space.  The following macros reassembly a key or data size back
+** into an integer.
+*/
+#define NKEY(b,h)  (SWAB16(b,h.nKey) + h.nKeyHi*65536)
+#define NDATA(b,h) (SWAB16(b,h.nData) + h.nDataHi*65536)
+
+/*
+** The minimum size of a complete Cell.  The Cell must contain a header
+** and at least 4 bytes of payload.
+*/
+#define MIN_CELL_SIZE  (sizeof(CellHdr)+4)
+
+/*
+** The maximum number of database entries that can be held in a single
+** page of the database. 
+*/
+#define MX_CELL ((SQLITE_USABLE_SIZE-sizeof(PageHdr))/MIN_CELL_SIZE)
+
+/*
+** The amount of usable space on a single page of the BTree.  This is the
+** page size minus the overhead of the page header.
+*/
+#define USABLE_SPACE  (SQLITE_USABLE_SIZE - sizeof(PageHdr))
+
+/*
+** The maximum amount of payload (in bytes) that can be stored locally for
+** a database entry.  If the entry contains more data than this, the
+** extra goes onto overflow pages.
+**
+** This number is chosen so that at least 4 cells will fit on every page.
+*/
+#define MX_LOCAL_PAYLOAD ((USABLE_SPACE/4-(sizeof(CellHdr)+sizeof(Pgno)))&~3)
+
+/*
+** Data on a database page is stored as a linked list of Cell structures.
+** Both the key and the data are stored in aPayload[].  The key always comes
+** first.  The aPayload[] field grows as necessary to hold the key and data,
+** up to a maximum of MX_LOCAL_PAYLOAD bytes.  If the size of the key and
+** data combined exceeds MX_LOCAL_PAYLOAD bytes, then Cell.ovfl is the
+** page number of the first overflow page.
+**
+** Though this structure is fixed in size, the Cell on the database
+** page varies in size.  Every cell has a CellHdr and at least 4 bytes
+** of payload space.  Additional payload bytes (up to the maximum of
+** MX_LOCAL_PAYLOAD) and the Cell.ovfl value are allocated only as
+** needed.
+*/
+struct Cell {
+  CellHdr h;                        /* The cell header */
+  char aPayload[MX_LOCAL_PAYLOAD];  /* Key and data */
+  Pgno ovfl;                        /* The first overflow page */
+};
+
+/*
+** Free space on a page is remembered using a linked list of the FreeBlk
+** structures.  Space on a database page is allocated in increments of
+** at least 4 bytes and is always aligned to a 4-byte boundry.  The
+** linked list of FreeBlks is always kept in order by address.
+*/
+struct FreeBlk {
+  u16 iSize;      /* Number of bytes in this block of free space */
+  u16 iNext;      /* Index in MemPage.u.aDisk[] of the next free block */
+};
+
+/*
+** The number of bytes of payload that will fit on a single overflow page.
+*/
+#define OVERFLOW_SIZE (SQLITE_USABLE_SIZE-sizeof(Pgno))
+
+/*
+** When the key and data for a single entry in the BTree will not fit in
+** the MX_LOCAL_PAYLOAD bytes of space available on the database page,
+** then all extra bytes are written to a linked list of overflow pages.
+** Each overflow page is an instance of the following structure.
+**
+** Unused pages in the database are also represented by instances of
+** the OverflowPage structure.  The PageOne.freeList field is the
+** page number of the first page in a linked list of unused database
+** pages.
+*/
+struct OverflowPage {
+  Pgno iNext;
+  char aPayload[OVERFLOW_SIZE];
+};
+
+/*
+** The PageOne.freeList field points to a linked list of overflow pages
+** hold information about free pages.  The aPayload section of each
+** overflow page contains an instance of the following structure.  The
+** aFree[] array holds the page number of nFree unused pages in the disk
+** file.
+*/
+struct FreelistInfo {
+  int nFree;
+  Pgno aFree[(OVERFLOW_SIZE-sizeof(int))/sizeof(Pgno)];
+};
+
+/*
+** For every page in the database file, an instance of the following structure
+** is stored in memory.  The u.aDisk[] array contains the raw bits read from
+** the disk.  The rest is auxiliary information held in memory only. The
+** auxiliary info is only valid for regular database pages - it is not
+** used for overflow pages and pages on the freelist.
+**
+** Of particular interest in the auxiliary info is the apCell[] entry.  Each
+** apCell[] entry is a pointer to a Cell structure in u.aDisk[].  The cells are
+** put in this array so that they can be accessed in constant time, rather
+** than in linear time which would be needed if we had to walk the linked 
+** list on every access.
+**
+** Note that apCell[] contains enough space to hold up to two more Cells
+** than can possibly fit on one page.  In the steady state, every apCell[]
+** points to memory inside u.aDisk[].  But in the middle of an insert
+** operation, some apCell[] entries may temporarily point to data space
+** outside of u.aDisk[].  This is a transient situation that is tquickly
+** resolved.  But while it is happening, it is possible for a database
+** page to hold as many as two more cells than it might otherwise hold.
+** The extra two entries in apCell[] are an allowance for this situation.
+**
+** The pParent field points back to the parent page.  This allows us to
+** walk up the BTree from any leaf to the root.  Care must be taken to
+** unref() the parent page pointer when this page is no longer referenced.
+** The pageDestructor() routine handles that chore.
+*/
+struct MemPage {
+  union u_page_data {
+    char aDisk[SQLITE_PAGE_SIZE];  /* Page data stored on disk */
+    PageHdr hdr;                   /* Overlay page header */
+  } u;
+  u8 isInit;                     /* True if auxiliary data is initialized */
+  u8 idxShift;                   /* True if apCell[] indices have changed */
+  u8 isOverfull;                 /* Some apCell[] points outside u.aDisk[] */
+  MemPage *pParent;              /* The parent of this page.  NULL for root */
+  int idxParent;                 /* Index in pParent->apCell[] of this node */
+  int nFree;                     /* Number of free bytes in u.aDisk[] */
+  int nCell;                     /* Number of entries on this page */
+  Cell *apCell[MX_CELL+2];       /* All data entires in sorted order */
+};
+
+/*
+** The in-memory image of a disk page has the auxiliary information appended
+** to the end.  EXTRA_SIZE is the number of bytes of space needed to hold
+** that extra information.
+*/
+#define EXTRA_SIZE (sizeof(MemPage)-sizeof(union u_page_data))
+
+/*
+** Everything we need to know about an open database
+*/
+struct Btree {
+  BtOps *pOps;          /* Function table */
+  Pager *pPager;        /* The page cache */
+  BtCursor *pCursor;    /* A list of all open cursors */
+  PageOne *page1;       /* First page of the database */
+  u8 inTrans;           /* True if a transaction is in progress */
+  u8 inCkpt;            /* True if there is a checkpoint on the transaction */
+  u8 readOnly;          /* True if the underlying file is readonly */
+  u8 needSwab;          /* Need to byte-swapping */
+};
+typedef Btree Bt;
+
+/*
+** A cursor is a pointer to a particular entry in the BTree.
+** The entry is identified by its MemPage and the index in
+** MemPage.apCell[] of the entry.
+*/
+struct BtCursor {
+  BtCursorOps *pOps;        /* Function table */
+  Btree *pBt;               /* The Btree to which this cursor belongs */
+  BtCursor *pNext, *pPrev;  /* Forms a linked list of all cursors */
+  BtCursor *pShared;        /* Loop of cursors with the same root page */
+  Pgno pgnoRoot;            /* The root page of this tree */
+  MemPage *pPage;           /* Page that contains the entry */
+  int idx;                  /* Index of the entry in pPage->apCell[] */
+  u8 wrFlag;                /* True if writable */
+  u8 eSkip;                 /* Determines if next step operation is a no-op */
+  u8 iMatch;                /* compare result from last sqliteBtreeMoveto() */
+};
+
+/*
+** Legal values for BtCursor.eSkip.
+*/
+#define SKIP_NONE     0   /* Always step the cursor */
+#define SKIP_NEXT     1   /* The next sqliteBtreeNext() is a no-op */
+#define SKIP_PREV     2   /* The next sqliteBtreePrevious() is a no-op */
+#define SKIP_INVALID  3   /* Calls to Next() and Previous() are invalid */
+
+/* Forward declarations */
+static int fileBtreeCloseCursor(BtCursor *pCur);
+
+/*
+** Routines for byte swapping.
+*/
+u16 swab16(u16 x){
+  return ((x & 0xff)<<8) | ((x>>8)&0xff);
+}
+u32 swab32(u32 x){
+  return ((x & 0xff)<<24) | ((x & 0xff00)<<8) |
+         ((x>>8) & 0xff00) | ((x>>24)&0xff);
+}
+
+/*
+** Compute the total number of bytes that a Cell needs on the main
+** database page.  The number returned includes the Cell header,
+** local payload storage, and the pointer to overflow pages (if
+** applicable).  Additional space allocated on overflow pages
+** is NOT included in the value returned from this routine.
+*/
+static int cellSize(Btree *pBt, Cell *pCell){
+  int n = NKEY(pBt, pCell->h) + NDATA(pBt, pCell->h);
+  if( n>MX_LOCAL_PAYLOAD ){
+    n = MX_LOCAL_PAYLOAD + sizeof(Pgno);
+  }else{
+    n = ROUNDUP(n);
+  }
+  n += sizeof(CellHdr);
+  return n;
+}
+
+/*
+** Defragment the page given.  All Cells are moved to the
+** beginning of the page and all free space is collected 
+** into one big FreeBlk at the end of the page.
+*/
+static void defragmentPage(Btree *pBt, MemPage *pPage){
+  int pc, i, n;
+  FreeBlk *pFBlk;
+  char newPage[SQLITE_USABLE_SIZE];
+
+  assert( sqlitepager_iswriteable(pPage) );
+  assert( pPage->isInit );
+  pc = sizeof(PageHdr);
+  pPage->u.hdr.firstCell = SWAB16(pBt, pc);
+  memcpy(newPage, pPage->u.aDisk, pc);
+  for(i=0; i<pPage->nCell; i++){
+    Cell *pCell = pPage->apCell[i];
+
+    /* This routine should never be called on an overfull page.  The
+    ** following asserts verify that constraint. */
+    assert( Addr(pCell) > Addr(pPage) );
+    assert( Addr(pCell) < Addr(pPage) + SQLITE_USABLE_SIZE );
+
+    n = cellSize(pBt, pCell);
+    pCell->h.iNext = SWAB16(pBt, pc + n);
+    memcpy(&newPage[pc], pCell, n);
+    pPage->apCell[i] = (Cell*)&pPage->u.aDisk[pc];
+    pc += n;
+  }
+  assert( pPage->nFree==SQLITE_USABLE_SIZE-pc );
+  memcpy(pPage->u.aDisk, newPage, pc);
+  if( pPage->nCell>0 ){
+    pPage->apCell[pPage->nCell-1]->h.iNext = 0;
+  }
+  pFBlk = (FreeBlk*)&pPage->u.aDisk[pc];
+  pFBlk->iSize = SWAB16(pBt, SQLITE_USABLE_SIZE - pc);
+  pFBlk->iNext = 0;
+  pPage->u.hdr.firstFree = SWAB16(pBt, pc);
+  memset(&pFBlk[1], 0, SQLITE_USABLE_SIZE - pc - sizeof(FreeBlk));
+}
+
+/*
+** Allocate nByte bytes of space on a page.  nByte must be a 
+** multiple of 4.
+**
+** Return the index into pPage->u.aDisk[] 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(Btree *pBt, MemPage *pPage, int nByte){
+  FreeBlk *p;
+  u16 *pIdx;
+  int start;
+  int iSize;
+#ifndef NDEBUG
+  int cnt = 0;
+#endif
+
+  assert( sqlitepager_iswriteable(pPage) );
+  assert( nByte==ROUNDUP(nByte) );
+  assert( pPage->isInit );
+  if( pPage->nFree<nByte || pPage->isOverfull ) return 0;
+  pIdx = &pPage->u.hdr.firstFree;
+  p = (FreeBlk*)&pPage->u.aDisk[SWAB16(pBt, *pIdx)];
+  while( (iSize = SWAB16(pBt, p->iSize))<nByte ){
+    assert( cnt++ < SQLITE_USABLE_SIZE/4 );
+    if( p->iNext==0 ){
+      defragmentPage(pBt, pPage);
+      pIdx = &pPage->u.hdr.firstFree;
+    }else{
+      pIdx = &p->iNext;
+    }
+    p = (FreeBlk*)&pPage->u.aDisk[SWAB16(pBt, *pIdx)];
+  }
+  if( iSize==nByte ){
+    start = SWAB16(pBt, *pIdx);
+    *pIdx = p->iNext;
+  }else{
+    FreeBlk *pNew;
+    start = SWAB16(pBt, *pIdx);
+    pNew = (FreeBlk*)&pPage->u.aDisk[start + nByte];
+    pNew->iNext = p->iNext;
+    pNew->iSize = SWAB16(pBt, iSize - nByte);
+    *pIdx = SWAB16(pBt, start + nByte);
+  }
+  pPage->nFree -= nByte;
+  return start;
+}
+
+/*
+** Return a section of the MemPage.u.aDisk[] to the freelist.
+** The first byte of the new free block is pPage->u.aDisk[start]
+** and the size of the block is "size" bytes.  Size must be
+** a multiple of 4.
+**
+** Most of the effort here is involved in coalesing adjacent
+** free blocks into a single big free block.
+*/
+static void freeSpace(Btree *pBt, MemPage *pPage, int start, int size){
+  int end = start + size;
+  u16 *pIdx, idx;
+  FreeBlk *pFBlk;
+  FreeBlk *pNew;
+  FreeBlk *pNext;
+  int iSize;
+
+  assert( sqlitepager_iswriteable(pPage) );
+  assert( size == ROUNDUP(size) );
+  assert( start == ROUNDUP(start) );
+  assert( pPage->isInit );
+  pIdx = &pPage->u.hdr.firstFree;
+  idx = SWAB16(pBt, *pIdx);
+  while( idx!=0 && idx<start ){
+    pFBlk = (FreeBlk*)&pPage->u.aDisk[idx];
+    iSize = SWAB16(pBt, pFBlk->iSize);
+    if( idx + iSize == start ){
+      pFBlk->iSize = SWAB16(pBt, iSize + size);
+      if( idx + iSize + size == SWAB16(pBt, pFBlk->iNext) ){
+        pNext = (FreeBlk*)&pPage->u.aDisk[idx + iSize + size];
+        if( pBt->needSwab ){
+          pFBlk->iSize = swab16((u16)swab16(pNext->iSize)+iSize+size);
+        }else{
+          pFBlk->iSize += pNext->iSize;
+        }
+        pFBlk->iNext = pNext->iNext;
+      }
+      pPage->nFree += size;
+      return;
+    }
+    pIdx = &pFBlk->iNext;
+    idx = SWAB16(pBt, *pIdx);
+  }
+  pNew = (FreeBlk*)&pPage->u.aDisk[start];
+  if( idx != end ){
+    pNew->iSize = SWAB16(pBt, size);
+    pNew->iNext = SWAB16(pBt, idx);
+  }else{
+    pNext = (FreeBlk*)&pPage->u.aDisk[idx];
+    pNew->iSize = SWAB16(pBt, size + SWAB16(pBt, pNext->iSize));
+    pNew->iNext = pNext->iNext;
+  }
+  *pIdx = SWAB16(pBt, start);
+  pPage->nFree += size;
+}
+
+/*
+** 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 the
+** BTree (usually page 2) 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.
+*/
+static int initPage(Bt *pBt, MemPage *pPage, Pgno pgnoThis, MemPage *pParent){
+  int idx;           /* An index into pPage->u.aDisk[] */
+  Cell *pCell;       /* A pointer to a Cell in pPage->u.aDisk[] */
+  FreeBlk *pFBlk;    /* A pointer to a free block in pPage->u.aDisk[] */
+  int sz;            /* The size of a Cell in bytes */
+  int freeSpace;     /* Amount of free space on the page */
+
+  if( pPage->pParent ){
+    assert( pPage->pParent==pParent );
+    return SQLITE_OK;
+  }
+  if( pParent ){
+    pPage->pParent = pParent;
+    sqlitepager_ref(pParent);
+  }
+  if( pPage->isInit ) return SQLITE_OK;
+  pPage->isInit = 1;
+  pPage->nCell = 0;
+  freeSpace = USABLE_SPACE;
+  idx = SWAB16(pBt, pPage->u.hdr.firstCell);
+  while( idx!=0 ){
+    if( idx>SQLITE_USABLE_SIZE-MIN_CELL_SIZE ) goto page_format_error;
+    if( idx<sizeof(PageHdr) ) goto page_format_error;
+    if( idx!=ROUNDUP(idx) ) goto page_format_error;
+    pCell = (Cell*)&pPage->u.aDisk[idx];
+    sz = cellSize(pBt, pCell);
+    if( idx+sz > SQLITE_USABLE_SIZE ) goto page_format_error;
+    freeSpace -= sz;
+    pPage->apCell[pPage->nCell++] = pCell;
+    idx = SWAB16(pBt, pCell->h.iNext);
+  }
+  pPage->nFree = 0;
+  idx = SWAB16(pBt, pPage->u.hdr.firstFree);
+  while( idx!=0 ){
+    int iNext;
+    if( idx>SQLITE_USABLE_SIZE-sizeof(FreeBlk) ) goto page_format_error;
+    if( idx<sizeof(PageHdr) ) goto page_format_error;
+    pFBlk = (FreeBlk*)&pPage->u.aDisk[idx];
+    pPage->nFree += SWAB16(pBt, pFBlk->iSize);
+    iNext = SWAB16(pBt, pFBlk->iNext);
+    if( iNext>0 && iNext <= idx ) goto page_format_error;
+    idx = iNext;
+  }
+  if( pPage->nCell==0 && pPage->nFree==0 ){
+    /* As a special case, an uninitialized root page appears to be
+    ** an empty database */
+    return SQLITE_OK;
+  }
+  if( pPage->nFree!=freeSpace ) goto page_format_error;
+  return SQLITE_OK;
+
+page_format_error:
+  return SQLITE_CORRUPT;
+}
+
+/*
+** Set up a raw page so that it looks like a database page holding
+** no entries.
+*/
+static void zeroPage(Btree *pBt, MemPage *pPage){
+  PageHdr *pHdr;
+  FreeBlk *pFBlk;
+  assert( sqlitepager_iswriteable(pPage) );
+  memset(pPage, 0, SQLITE_USABLE_SIZE);
+  pHdr = &pPage->u.hdr;
+  pHdr->firstCell = 0;
+  pHdr->firstFree = SWAB16(pBt, sizeof(*pHdr));
+  pFBlk = (FreeBlk*)&pHdr[1];
+  pFBlk->iNext = 0;
+  pPage->nFree = SQLITE_USABLE_SIZE - sizeof(*pHdr);
+  pFBlk->iSize = SWAB16(pBt, pPage->nFree);
+  pPage->nCell = 0;
+  pPage->isOverfull = 0;
+}
+
+/*
+** 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(void *pData){
+  MemPage *pPage = (MemPage*)pData;
+  if( pPage->pParent ){
+    MemPage *pParent = pPage->pParent;
+    pPage->pParent = 0;
+    sqlitepager_unref(pParent);
+  }
+}
+
+/*
+** Open a new database.
+**
+** Actually, this routine just sets up the internal data structures
+** for accessing the database.  We do not open the database file 
+** until the first page is loaded.
+**
+** 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 sqliteBtreeClose() is called.
+*/
+int sqliteBtreeOpen(
+  const char *zFilename,    /* Name of the file containing the BTree database */
+  int omitJournal,          /* if TRUE then do not journal this file */
+  int nCache,               /* How many pages in the page cache */
+  Btree **ppBtree           /* Pointer to new Btree object written here */
+){
+  Btree *pBt;
+  int rc;
+
+  /*
+  ** 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(u32)==4 );
+  assert( sizeof(u16)==2 );
+  assert( sizeof(Pgno)==4 );
+  assert( sizeof(PageHdr)==8 );
+  assert( sizeof(CellHdr)==12 );
+  assert( sizeof(FreeBlk)==4 );
+  assert( sizeof(OverflowPage)==SQLITE_USABLE_SIZE );
+  assert( sizeof(FreelistInfo)==OVERFLOW_SIZE );
+  assert( sizeof(ptr)==sizeof(char*) );
+  assert( sizeof(uptr)==sizeof(ptr) );
+
+  pBt = sqliteMalloc( sizeof(*pBt) );
+  if( pBt==0 ){
+    *ppBtree = 0;
+    return SQLITE_NOMEM;
+  }
+  if( nCache<10 ) nCache = 10;
+  rc = sqlitepager_open(&pBt->pPager, zFilename, nCache, EXTRA_SIZE,
+                        !omitJournal);
+  if( rc!=SQLITE_OK ){
+    if( pBt->pPager ) sqlitepager_close(pBt->pPager);
+    sqliteFree(pBt);
+    *ppBtree = 0;
+    return rc;
+  }
+  sqlitepager_set_destructor(pBt->pPager, pageDestructor);
+  pBt->pCursor = 0;
+  pBt->page1 = 0;
+  pBt->readOnly = sqlitepager_isreadonly(pBt->pPager);
+  pBt->pOps = &sqliteBtreeOps;
+  *ppBtree = pBt;
+  return SQLITE_OK;
+}
+
+/*
+** Close an open database and invalidate all cursors.
+*/
+static int fileBtreeClose(Btree *pBt){
+  while( pBt->pCursor ){
+    fileBtreeCloseCursor(pBt->pCursor);
+  }
+  sqlitepager_close(pBt->pPager);
+  sqliteFree(pBt);
+  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.
+*/
+static int fileBtreeSetCacheSize(Btree *pBt, int mxPage){
+  sqlitepager_set_cachesize(pBt->pPager, mxPage);
+  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.
+*/
+static int fileBtreeSetSafetyLevel(Btree *pBt, int level){
+  sqlitepager_set_safety_level(pBt->pPager, level);
+  return SQLITE_OK;
+}
+
+/*
+** Get a reference to page1 of the database file.  This will
+** also actquire 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.  SQLITE_PROTOCOL is returned
+** if there is a locking protocol violation.
+*/
+static int lockBtree(Btree *pBt){
+  int rc;
+  if( pBt->page1 ) return SQLITE_OK;
+  rc = sqlitepager_get(pBt->pPager, 1, (void**)&pBt->page1);
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Do some checking to help insure the file we opened really is
+  ** a valid database file. 
+  */
+  if( sqlitepager_pagecount(pBt->pPager)>0 ){
+    PageOne *pP1 = pBt->page1;
+    if( strcmp(pP1->zMagic,zMagicHeader)!=0 ||
+          (pP1->iMagic!=MAGIC && swab32(pP1->iMagic)!=MAGIC) ){
+      rc = SQLITE_NOTADB;
+      goto page1_init_failed;
+    }
+    pBt->needSwab = pP1->iMagic!=MAGIC;
+  }
+  return rc;
+
+page1_init_failed:
+  sqlitepager_unref(pBt->page1);
+  pBt->page1 = 0;
+  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(Btree *pBt){
+  if( pBt->inTrans==0 && pBt->pCursor==0 && pBt->page1!=0 ){
+    sqlitepager_unref(pBt->page1);
+    pBt->page1 = 0;
+    pBt->inTrans = 0;
+    pBt->inCkpt = 0;
+  }
+}
+
+/*
+** Create a new database by initializing the first two pages of the
+** file.
+*/
+static int newDatabase(Btree *pBt){
+  MemPage *pRoot;
+  PageOne *pP1;
+  int rc;
+  if( sqlitepager_pagecount(pBt->pPager)>1 ) return SQLITE_OK;
+  pP1 = pBt->page1;
+  rc = sqlitepager_write(pBt->page1);
+  if( rc ) return rc;
+  rc = sqlitepager_get(pBt->pPager, 2, (void**)&pRoot);
+  if( rc ) return rc;
+  rc = sqlitepager_write(pRoot);
+  if( rc ){
+    sqlitepager_unref(pRoot);
+    return rc;
+  }
+  strcpy(pP1->zMagic, zMagicHeader);
+  if( btree_native_byte_order ){
+    pP1->iMagic = MAGIC;
+    pBt->needSwab = 0;
+  }else{
+    pP1->iMagic = swab32(MAGIC);
+    pBt->needSwab = 1;
+  }
+  zeroPage(pBt, pRoot);
+  sqlitepager_unref(pRoot);
+  return SQLITE_OK;
+}
+
+/*
+** Attempt to start a new transaction.
+**
+** A transaction must be started before attempting any changes
+** to the database.  None of the following routines will work
+** unless a transaction is started first:
+**
+**      sqliteBtreeCreateTable()
+**      sqliteBtreeCreateIndex()
+**      sqliteBtreeClearTable()
+**      sqliteBtreeDropTable()
+**      sqliteBtreeInsert()
+**      sqliteBtreeDelete()
+**      sqliteBtreeUpdateMeta()
+*/
+static int fileBtreeBeginTrans(Btree *pBt){
+  int rc;
+  if( pBt->inTrans ) return SQLITE_ERROR;
+  if( pBt->readOnly ) return SQLITE_READONLY;
+  if( pBt->page1==0 ){
+    rc = lockBtree(pBt);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+  }
+  rc = sqlitepager_begin(pBt->page1);
+  if( rc==SQLITE_OK ){
+    rc = newDatabase(pBt);
+  }
+  if( rc==SQLITE_OK ){
+    pBt->inTrans = 1;
+    pBt->inCkpt = 0;
+  }else{
+    unlockBtreeIfUnused(pBt);
+  }
+  return rc;
+}
+
+/*
+** Commit the transaction currently in progress.
+**
+** This will release the write lock on the database file.  If there
+** are no active cursors, it also releases the read lock.
+*/
+static int fileBtreeCommit(Btree *pBt){
+  int rc;
+  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_commit(pBt->pPager);
+  pBt->inTrans = 0;
+  pBt->inCkpt = 0;
+  unlockBtreeIfUnused(pBt);
+  return rc;
+}
+
+/*
+** 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.
+*/
+static int fileBtreeRollback(Btree *pBt){
+  int rc;
+  BtCursor *pCur;
+  if( pBt->inTrans==0 ) return SQLITE_OK;
+  pBt->inTrans = 0;
+  pBt->inCkpt = 0;
+  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_rollback(pBt->pPager);
+  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
+    if( pCur->pPage && pCur->pPage->isInit==0 ){
+      sqlitepager_unref(pCur->pPage);
+      pCur->pPage = 0;
+    }
+  }
+  unlockBtreeIfUnused(pBt);
+  return rc;
+}
+
+/*
+** Set the checkpoint for the current transaction.  The checkpoint serves
+** as a sub-transaction that can be rolled back independently of the
+** main transaction.  You must start a transaction before starting a
+** checkpoint.  The checkpoint is ended automatically if the transaction
+** commits or rolls back.
+**
+** Only one checkpoint may be active at a time.  It is an error to try
+** to start a new checkpoint if another checkpoint is already active.
+*/
+static int fileBtreeBeginCkpt(Btree *pBt){
+  int rc;
+  if( !pBt->inTrans || pBt->inCkpt ){
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_ckpt_begin(pBt->pPager);
+  pBt->inCkpt = 1;
+  return rc;
+}
+
+
+/*
+** Commit a checkpoint to transaction currently in progress.  If no
+** checkpoint is active, this is a no-op.
+*/
+static int fileBtreeCommitCkpt(Btree *pBt){
+  int rc;
+  if( pBt->inCkpt && !pBt->readOnly ){
+    rc = sqlitepager_ckpt_commit(pBt->pPager);
+  }else{
+    rc = SQLITE_OK;
+  }
+  pBt->inCkpt = 0;
+  return rc;
+}
+
+/*
+** Rollback the checkpoint to the current transaction.  If there
+** is no active checkpoint or transaction, this routine is a no-op.
+**
+** 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.
+*/
+static int fileBtreeRollbackCkpt(Btree *pBt){
+  int rc;
+  BtCursor *pCur;
+  if( pBt->inCkpt==0 || pBt->readOnly ) return SQLITE_OK;
+  rc = sqlitepager_ckpt_rollback(pBt->pPager);
+  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
+    if( pCur->pPage && pCur->pPage->isInit==0 ){
+      sqlitepager_unref(pCur->pPage);
+      pCur->pPage = 0;
+    }
+  }
+  pBt->inCkpt = 0;
+  return rc;
+}
+
+/*
+** Create a new cursor for the BTree whose root is on the page
+** iTable.  The act of actquiring 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:  No other cursors may be open with wrFlag==0 on the same table
+**
+** 3:  The database must be writable (not on read-only media)
+**
+** 4:  There must be an active transaction.
+**
+** Condition 2 warrants further discussion.  If any cursor is opened
+** on a table with wrFlag==0, that prevents all other cursors from
+** writing to that table.  This is a kind of "read-lock".  When a cursor
+** is opened with wrFlag==0 it is guaranteed that the table will not
+** change as long as the cursor is open.  This allows the cursor to
+** do a sequential scan of the table without having to worry about
+** entries being inserted or deleted during the scan.  Cursors should
+** be opened with wrFlag==0 only if this read-lock property is needed.
+** That is to say, cursors should be opened with wrFlag==0 only if they
+** intend to use the sqliteBtreeNext() system call.  All other cursors
+** should be opened with wrFlag==1 even if they never really intend
+** to write.
+** 
+** 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 actquired
+** will not work correctly.
+*/
+static int fileBtreeCursor(Btree *pBt, int iTable, int wrFlag, BtCursor **ppCur){
+  int rc;
+  BtCursor *pCur, *pRing;
+
+  if( pBt->page1==0 ){
+    rc = lockBtree(pBt);
+    if( rc!=SQLITE_OK ){
+      *ppCur = 0;
+      return rc;
+    }
+  }
+  pCur = sqliteMalloc( sizeof(*pCur) );
+  if( pCur==0 ){
+    rc = SQLITE_NOMEM;
+    goto create_cursor_exception;
+  }
+  pCur->pgnoRoot = (Pgno)iTable;
+  rc = sqlitepager_get(pBt->pPager, pCur->pgnoRoot, (void**)&pCur->pPage);
+  if( rc!=SQLITE_OK ){
+    goto create_cursor_exception;
+  }
+  rc = initPage(pBt, pCur->pPage, pCur->pgnoRoot, 0);
+  if( rc!=SQLITE_OK ){
+    goto create_cursor_exception;
+  }
+  pCur->pOps = &sqliteBtreeCursorOps;
+  pCur->pBt = pBt;
+  pCur->wrFlag = wrFlag;
+  pCur->idx = 0;
+  pCur->eSkip = SKIP_INVALID;
+  pCur->pNext = pBt->pCursor;
+  if( pCur->pNext ){
+    pCur->pNext->pPrev = pCur;
+  }
+  pCur->pPrev = 0;
+  pRing = pBt->pCursor;
+  while( pRing && pRing->pgnoRoot!=pCur->pgnoRoot ){ pRing = pRing->pNext; }
+  if( pRing ){
+    pCur->pShared = pRing->pShared;
+    pRing->pShared = pCur;
+  }else{
+    pCur->pShared = pCur;
+  }
+  pBt->pCursor = pCur;
+  *ppCur = pCur;
+  return SQLITE_OK;
+
+create_cursor_exception:
+  *ppCur = 0;
+  if( pCur ){
+    if( pCur->pPage ) sqlitepager_unref(pCur->pPage);
+    sqliteFree(pCur);
+  }
+  unlockBtreeIfUnused(pBt);
+  return rc;
+}
+
+/*
+** Close a cursor.  The read lock on the database file is released
+** when the last cursor is closed.
+*/
+static int fileBtreeCloseCursor(BtCursor *pCur){
+  Btree *pBt = pCur->pBt;
+  if( pCur->pPrev ){
+    pCur->pPrev->pNext = pCur->pNext;
+  }else{
+    pBt->pCursor = pCur->pNext;
+  }
+  if( pCur->pNext ){
+    pCur->pNext->pPrev = pCur->pPrev;
+  }
+  if( pCur->pPage ){
+    sqlitepager_unref(pCur->pPage);
+  }
+  if( pCur->pShared!=pCur ){
+    BtCursor *pRing = pCur->pShared;
+    while( pRing->pShared!=pCur ){ pRing = pRing->pShared; }
+    pRing->pShared = pCur->pShared;
+  }
+  unlockBtreeIfUnused(pBt);
+  sqliteFree(pCur);
+  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.
+*/
+static void getTempCursor(BtCursor *pCur, BtCursor *pTempCur){
+  memcpy(pTempCur, pCur, sizeof(*pCur));
+  pTempCur->pNext = 0;
+  pTempCur->pPrev = 0;
+  if( pTempCur->pPage ){
+    sqlitepager_ref(pTempCur->pPage);
+  }
+}
+
+/*
+** Delete a temporary cursor such as was made by the CreateTemporaryCursor()
+** function above.
+*/
+static void releaseTempCursor(BtCursor *pCur){
+  if( pCur->pPage ){
+    sqlitepager_unref(pCur->pPage);
+  }
+}
+
+/*
+** Set *pSize to the number of bytes of key 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.
+*/
+static int fileBtreeKeySize(BtCursor *pCur, int *pSize){
+  Cell *pCell;
+  MemPage *pPage;
+
+  pPage = pCur->pPage;
+  assert( pPage!=0 );
+  if( pCur->idx >= pPage->nCell ){
+    *pSize = 0;
+  }else{
+    pCell = pPage->apCell[pCur->idx];
+    *pSize = NKEY(pCur->pBt, pCell->h);
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Read payload information from the entry that the pCur cursor is
+** pointing to.  Begin reading the payload at "offset" and read
+** a total of "amt" bytes.  Put the result in zBuf.
+**
+** This routine does not make a distinction between key and data.
+** It just reads bytes from the payload area.
+*/
+static int getPayload(BtCursor *pCur, int offset, int amt, char *zBuf){
+  char *aPayload;
+  Pgno nextPage;
+  int rc;
+  Btree *pBt = pCur->pBt;
+  assert( pCur!=0 && pCur->pPage!=0 );
+  assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
+  aPayload = pCur->pPage->apCell[pCur->idx]->aPayload;
+  if( offset<MX_LOCAL_PAYLOAD ){
+    int a = amt;
+    if( a+offset>MX_LOCAL_PAYLOAD ){
+      a = MX_LOCAL_PAYLOAD - offset;
+    }
+    memcpy(zBuf, &aPayload[offset], a);
+    if( a==amt ){
+      return SQLITE_OK;
+    }
+    offset = 0;
+    zBuf += a;
+    amt -= a;
+  }else{
+    offset -= MX_LOCAL_PAYLOAD;
+  }
+  if( amt>0 ){
+    nextPage = SWAB32(pBt, pCur->pPage->apCell[pCur->idx]->ovfl);
+  }
+  while( amt>0 && nextPage ){
+    OverflowPage *pOvfl;
+    rc = sqlitepager_get(pBt->pPager, nextPage, (void**)&pOvfl);
+    if( rc!=0 ){
+      return rc;
+    }
+    nextPage = SWAB32(pBt, pOvfl->iNext);
+    if( offset<OVERFLOW_SIZE ){
+      int a = amt;
+      if( a + offset > OVERFLOW_SIZE ){
+        a = OVERFLOW_SIZE - offset;
+      }
+      memcpy(zBuf, &pOvfl->aPayload[offset], a);
+      offset = 0;
+      amt -= a;
+      zBuf += a;
+    }else{
+      offset -= OVERFLOW_SIZE;
+    }
+    sqlitepager_unref(pOvfl);
+  }
+  if( amt>0 ){
+    return SQLITE_CORRUPT;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Read part of the key associated with cursor pCur.  A maximum
+** of "amt" bytes will be transfered into zBuf[].  The transfer
+** begins at "offset".  The number of bytes actually read is
+** returned. 
+**
+** Change:  It used to be that the amount returned will be smaller
+** than the amount requested if there are not enough bytes in the key
+** to satisfy the request.  But now, it must be the case that there
+** is enough data available to satisfy the request.  If not, an exception
+** is raised.  The change was made in an effort to boost performance
+** by eliminating unneeded tests.
+*/
+static int fileBtreeKey(BtCursor *pCur, int offset, int amt, char *zBuf){
+  MemPage *pPage;
+
+  assert( amt>=0 );
+  assert( offset>=0 );
+  assert( pCur->pPage!=0 );
+  pPage = pCur->pPage;
+  if( pCur->idx >= pPage->nCell ){
+    return 0;
+  }
+  assert( amt+offset <= NKEY(pCur->pBt, pPage->apCell[pCur->idx]->h) );
+  getPayload(pCur, offset, amt, zBuf);
+  return amt;
+}
+
+/*
+** 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.
+*/
+static int fileBtreeDataSize(BtCursor *pCur, int *pSize){
+  Cell *pCell;
+  MemPage *pPage;
+
+  pPage = pCur->pPage;
+  assert( pPage!=0 );
+  if( pCur->idx >= pPage->nCell ){
+    *pSize = 0;
+  }else{
+    pCell = pPage->apCell[pCur->idx];
+    *pSize = NDATA(pCur->pBt, pCell->h);
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Read part of the data associated with cursor pCur.  A maximum
+** of "amt" bytes will be transfered into zBuf[].  The transfer
+** begins at "offset".  The number of bytes actually read is
+** returned.  The amount returned will be smaller than the
+** amount requested if there are not enough bytes in the data
+** to satisfy the request.
+*/
+static int fileBtreeData(BtCursor *pCur, int offset, int amt, char *zBuf){
+  Cell *pCell;
+  MemPage *pPage;
+
+  assert( amt>=0 );
+  assert( offset>=0 );
+  assert( pCur->pPage!=0 );
+  pPage = pCur->pPage;
+  if( pCur->idx >= pPage->nCell ){
+    return 0;
+  }
+  pCell = pPage->apCell[pCur->idx];
+  assert( amt+offset <= NDATA(pCur->pBt, pCell->h) );
+  getPayload(pCur, offset + NKEY(pCur->pBt, pCell->h), amt, zBuf);
+  return amt;
+}
+
+/*
+** Compare an external key against the key on the entry that pCur points to.
+**
+** The external key is pKey and is nKey bytes long.  The last nIgnore bytes
+** of the key associated with pCur are ignored, as if they do not exist.
+** (The normal case is for nIgnore to be zero in which case the entire
+** internal key is used in the comparison.)
+**
+** The comparison result is written to *pRes as follows:
+**
+**    *pRes<0    This means pCur<pKey
+**
+**    *pRes==0   This means pCur==pKey for all nKey bytes
+**
+**    *pRes>0    This means pCur>pKey
+**
+** When one key is an exact prefix of the other, the shorter key is
+** considered less than the longer one.  In order to be equal the
+** keys must be exactly the same length. (The length of the pCur key
+** is the actual key length minus nIgnore bytes.)
+*/
+static int fileBtreeKeyCompare(
+  BtCursor *pCur,       /* Pointer to entry to compare against */
+  const void *pKey,     /* Key to compare against entry that pCur points to */
+  int nKey,             /* Number of bytes in pKey */
+  int nIgnore,          /* Ignore this many bytes at the end of pCur */
+  int *pResult          /* Write the result here */
+){
+  Pgno nextPage;
+  int n, c, rc, nLocal;
+  Cell *pCell;
+  Btree *pBt = pCur->pBt;
+  const char *zKey  = (const char*)pKey;
+
+  assert( pCur->pPage );
+  assert( pCur->idx>=0 && pCur->idx<pCur->pPage->nCell );
+  pCell = pCur->pPage->apCell[pCur->idx];
+  nLocal = NKEY(pBt, pCell->h) - nIgnore;
+  if( nLocal<0 ) nLocal = 0;
+  n = nKey<nLocal ? nKey : nLocal;
+  if( n>MX_LOCAL_PAYLOAD ){
+    n = MX_LOCAL_PAYLOAD;
+  }
+  c = memcmp(pCell->aPayload, zKey, n);
+  if( c!=0 ){
+    *pResult = c;
+    return SQLITE_OK;
+  }
+  zKey += n;
+  nKey -= n;
+  nLocal -= n;
+  nextPage = SWAB32(pBt, pCell->ovfl);
+  while( nKey>0 && nLocal>0 ){
+    OverflowPage *pOvfl;
+    if( nextPage==0 ){
+      return SQLITE_CORRUPT;
+    }
+    rc = sqlitepager_get(pBt->pPager, nextPage, (void**)&pOvfl);
+    if( rc ){
+      return rc;
+    }
+    nextPage = SWAB32(pBt, pOvfl->iNext);
+    n = nKey<nLocal ? nKey : nLocal;
+    if( n>OVERFLOW_SIZE ){
+      n = OVERFLOW_SIZE;
+    }
+    c = memcmp(pOvfl->aPayload, zKey, n);
+    sqlitepager_unref(pOvfl);
+    if( c!=0 ){
+      *pResult = c;
+      return SQLITE_OK;
+    }
+    nKey -= n;
+    nLocal -= n;
+    zKey += n;
+  }
+  if( c==0 ){
+    c = nLocal - nKey;
+  }
+  *pResult = c;
+  return SQLITE_OK;
+}
+
+/*
+** Move the cursor down to a new child page.  The newPgno argument is the
+** page number of the child page in the byte order of the disk image.
+*/
+static int moveToChild(BtCursor *pCur, int newPgno){
+  int rc;
+  MemPage *pNewPage;
+  Btree *pBt = pCur->pBt;
+
+  newPgno = SWAB32(pBt, newPgno);
+  rc = sqlitepager_get(pBt->pPager, newPgno, (void**)&pNewPage);
+  if( rc ) return rc;
+  rc = initPage(pBt, pNewPage, newPgno, pCur->pPage);
+  if( rc ) return rc;
+  assert( pCur->idx>=pCur->pPage->nCell
+          || pCur->pPage->apCell[pCur->idx]->h.leftChild==SWAB32(pBt,newPgno) );
+  assert( pCur->idx<pCur->pPage->nCell
+          || pCur->pPage->u.hdr.rightChild==SWAB32(pBt,newPgno) );
+  pNewPage->idxParent = pCur->idx;
+  pCur->pPage->idxShift = 0;
+  sqlitepager_unref(pCur->pPage);
+  pCur->pPage = pNewPage;
+  pCur->idx = 0;
+  if( pNewPage->nCell<1 ){
+    return SQLITE_CORRUPT;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** 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.
+*/
+static void moveToParent(BtCursor *pCur){
+  Pgno oldPgno;
+  MemPage *pParent;
+  MemPage *pPage;
+  int idxParent;
+  pPage = pCur->pPage;
+  assert( pPage!=0 );
+  pParent = pPage->pParent;
+  assert( pParent!=0 );
+  idxParent = pPage->idxParent;
+  sqlitepager_ref(pParent);
+  sqlitepager_unref(pPage);
+  pCur->pPage = pParent;
+  assert( pParent->idxShift==0 );
+  if( pParent->idxShift==0 ){
+    pCur->idx = idxParent;
+#ifndef NDEBUG  
+    /* Verify that pCur->idx is the correct index to point back to the child
+    ** page we just came from 
+    */
+    oldPgno = SWAB32(pCur->pBt, sqlitepager_pagenumber(pPage));
+    if( pCur->idx<pParent->nCell ){
+      assert( pParent->apCell[idxParent]->h.leftChild==oldPgno );
+    }else{
+      assert( pParent->u.hdr.rightChild==oldPgno );
+    }
+#endif
+  }else{
+    /* The MemPage.idxShift flag indicates that cell indices might have 
+    ** changed since idxParent was set and hence idxParent might be out
+    ** of date.  So recompute the parent cell index by scanning all cells
+    ** and locating the one that points to the child we just came from.
+    */
+    int i;
+    pCur->idx = pParent->nCell;
+    oldPgno = SWAB32(pCur->pBt, sqlitepager_pagenumber(pPage));
+    for(i=0; i<pParent->nCell; i++){
+      if( pParent->apCell[i]->h.leftChild==oldPgno ){
+        pCur->idx = i;
+        break;
+      }
+    }
+  }
+}
+
+/*
+** Move the cursor to the root page
+*/
+static int moveToRoot(BtCursor *pCur){
+  MemPage *pNew;
+  int rc;
+  Btree *pBt = pCur->pBt;
+
+  rc = sqlitepager_get(pBt->pPager, pCur->pgnoRoot, (void**)&pNew);
+  if( rc ) return rc;
+  rc = initPage(pBt, pNew, pCur->pgnoRoot, 0);
+  if( rc ) return rc;
+  sqlitepager_unref(pCur->pPage);
+  pCur->pPage = pNew;
+  pCur->idx = 0;
+  return SQLITE_OK;
+}
+
+/*
+** Move the cursor down to the left-most leaf entry beneath the
+** entry to which it is currently pointing.
+*/
+static int moveToLeftmost(BtCursor *pCur){
+  Pgno pgno;
+  int rc;
+
+  while( (pgno = pCur->pPage->apCell[pCur->idx]->h.leftChild)!=0 ){
+    rc = moveToChild(pCur, pgno);
+    if( rc ) return rc;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** 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*.
+*/
+static int moveToRightmost(BtCursor *pCur){
+  Pgno pgno;
+  int rc;
+
+  while( (pgno = pCur->pPage->u.hdr.rightChild)!=0 ){
+    pCur->idx = pCur->pPage->nCell;
+    rc = moveToChild(pCur, pgno);
+    if( rc ) return rc;
+  }
+  pCur->idx = pCur->pPage->nCell - 1;
+  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.
+*/
+static int fileBtreeFirst(BtCursor *pCur, int *pRes){
+  int rc;
+  if( pCur->pPage==0 ) return SQLITE_ABORT;
+  rc = moveToRoot(pCur);
+  if( rc ) return rc;
+  if( pCur->pPage->nCell==0 ){
+    *pRes = 1;
+    return SQLITE_OK;
+  }
+  *pRes = 0;
+  rc = moveToLeftmost(pCur);
+  pCur->eSkip = SKIP_NONE;
+  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.
+*/
+static int fileBtreeLast(BtCursor *pCur, int *pRes){
+  int rc;
+  if( pCur->pPage==0 ) return SQLITE_ABORT;
+  rc = moveToRoot(pCur);
+  if( rc ) return rc;
+  assert( pCur->pPage->isInit );
+  if( pCur->pPage->nCell==0 ){
+    *pRes = 1;
+    return SQLITE_OK;
+  }
+  *pRes = 0;
+  rc = moveToRightmost(pCur);
+  pCur->eSkip = SKIP_NONE;
+  return rc;
+}
+
+/* Move the cursor so that it points to an entry near pKey.
+** Return a success code.
+**
+** 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 left pointing is stored in pCur->iMatch.  The same
+** value is also 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.
+*/
+static
+int fileBtreeMoveto(BtCursor *pCur, const void *pKey, int nKey, int *pRes){
+  int rc;
+  if( pCur->pPage==0 ) return SQLITE_ABORT;
+  pCur->eSkip = SKIP_NONE;
+  rc = moveToRoot(pCur);
+  if( rc ) return rc;
+  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;
+    while( lwr<=upr ){
+      pCur->idx = (lwr+upr)/2;
+      rc = fileBtreeKeyCompare(pCur, pKey, nKey, 0, &c);
+      if( rc ) return rc;
+      if( c==0 ){
+        pCur->iMatch = c;
+        if( pRes ) *pRes = 0;
+        return SQLITE_OK;
+      }
+      if( c<0 ){
+        lwr = pCur->idx+1;
+      }else{
+        upr = pCur->idx-1;
+      }
+    }
+    assert( lwr==upr+1 );
+    assert( pPage->isInit );
+    if( lwr>=pPage->nCell ){
+      chldPg = pPage->u.hdr.rightChild;
+    }else{
+      chldPg = pPage->apCell[lwr]->h.leftChild;
+    }
+    if( chldPg==0 ){
+      pCur->iMatch = c;
+      if( pRes ) *pRes = c;
+      return SQLITE_OK;
+    }
+    pCur->idx = lwr;
+    rc = moveToChild(pCur, chldPg);
+    if( rc ) return rc;
+  }
+  /* NOT REACHED */
+}
+
+/*
+** 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 fileBtreeNext(BtCursor *pCur, int *pRes){
+  int rc;
+  MemPage *pPage = pCur->pPage;
+  assert( pRes!=0 );
+  if( pPage==0 ){
+    *pRes = 1;
+    return SQLITE_ABORT;
+  }
+  assert( pPage->isInit );
+  assert( pCur->eSkip!=SKIP_INVALID );
+  if( pPage->nCell==0 ){
+    *pRes = 1;
+    return SQLITE_OK;
+  }
+  assert( pCur->idx<pPage->nCell );
+  if( pCur->eSkip==SKIP_NEXT ){
+    pCur->eSkip = SKIP_NONE;
+    *pRes = 0;
+    return SQLITE_OK;
+  }
+  pCur->eSkip = SKIP_NONE;
+  pCur->idx++;
+  if( pCur->idx>=pPage->nCell ){
+    if( pPage->u.hdr.rightChild ){
+      rc = moveToChild(pCur, pPage->u.hdr.rightChild);
+      if( rc ) return rc;
+      rc = moveToLeftmost(pCur);
+      *pRes = 0;
+      return rc;
+    }
+    do{
+      if( pPage->pParent==0 ){
+        *pRes = 1;
+        return SQLITE_OK;
+      }
+      moveToParent(pCur);
+      pPage = pCur->pPage;
+    }while( pCur->idx>=pPage->nCell );
+    *pRes = 0;
+    return SQLITE_OK;
+  }
+  *pRes = 0;
+  if( pPage->u.hdr.rightChild==0 ){
+    return SQLITE_OK;
+  }
+  rc = moveToLeftmost(pCur);
+  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 fileBtreePrevious(BtCursor *pCur, int *pRes){
+  int rc;
+  Pgno pgno;
+  MemPage *pPage;
+  pPage = pCur->pPage;
+  if( pPage==0 ){
+    *pRes = 1;
+    return SQLITE_ABORT;
+  }
+  assert( pPage->isInit );
+  assert( pCur->eSkip!=SKIP_INVALID );
+  if( pPage->nCell==0 ){
+    *pRes = 1;
+    return SQLITE_OK;
+  }
+  if( pCur->eSkip==SKIP_PREV ){
+    pCur->eSkip = SKIP_NONE;
+    *pRes = 0;
+    return SQLITE_OK;
+  }
+  pCur->eSkip = SKIP_NONE;
+  assert( pCur->idx>=0 );
+  if( (pgno = pPage->apCell[pCur->idx]->h.leftChild)!=0 ){
+    rc = moveToChild(pCur, pgno);
+    if( rc ) return rc;
+    rc = moveToRightmost(pCur);
+  }else{
+    while( pCur->idx==0 ){
+      if( pPage->pParent==0 ){
+        if( pRes ) *pRes = 1;
+        return SQLITE_OK;
+      }
+      moveToParent(pCur);
+      pPage = pCur->pPage;
+    }
+    pCur->idx--;
+    rc = SQLITE_OK;
+  }
+  *pRes = 0;
+  return rc;
+}
+
+/*
+** Allocate a new page from the database file.
+**
+** The new page is marked as dirty.  (In other words, sqlitepager_write()
+** has already been called on the new page.)  The new page has also
+** been referenced and the calling routine is responsible for calling
+** sqlitepager_unref() 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 sqlitepager_unref() 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.
+*/
+static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno, Pgno nearby){
+  PageOne *pPage1 = pBt->page1;
+  int rc;
+  if( pPage1->freeList ){
+    OverflowPage *pOvfl;
+    FreelistInfo *pInfo;
+
+    rc = sqlitepager_write(pPage1);
+    if( rc ) return rc;
+    SWAB_ADD(pBt, pPage1->nFree, -1);
+    rc = sqlitepager_get(pBt->pPager, SWAB32(pBt, pPage1->freeList),
+                        (void**)&pOvfl);
+    if( rc ) return rc;
+    rc = sqlitepager_write(pOvfl);
+    if( rc ){
+      sqlitepager_unref(pOvfl);
+      return rc;
+    }
+    pInfo = (FreelistInfo*)pOvfl->aPayload;
+    if( pInfo->nFree==0 ){
+      *pPgno = SWAB32(pBt, pPage1->freeList);
+      pPage1->freeList = pOvfl->iNext;
+      *ppPage = (MemPage*)pOvfl;
+    }else{
+      int closest, n;
+      n = SWAB32(pBt, pInfo->nFree);
+      if( n>1 && nearby>0 ){
+        int i, dist;
+        closest = 0;
+        dist = SWAB32(pBt, pInfo->aFree[0]) - nearby;
+        if( dist<0 ) dist = -dist;
+        for(i=1; i<n; i++){
+          int d2 = SWAB32(pBt, pInfo->aFree[i]) - nearby;
+          if( d2<0 ) d2 = -d2;
+          if( d2<dist ) closest = i;
+        }
+      }else{
+        closest = 0;
+      }
+      SWAB_ADD(pBt, pInfo->nFree, -1);
+      *pPgno = SWAB32(pBt, pInfo->aFree[closest]);
+      pInfo->aFree[closest] = pInfo->aFree[n-1];
+      rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
+      sqlitepager_unref(pOvfl);
+      if( rc==SQLITE_OK ){
+        sqlitepager_dont_rollback(*ppPage);
+        rc = sqlitepager_write(*ppPage);
+      }
+    }
+  }else{
+    *pPgno = sqlitepager_pagecount(pBt->pPager) + 1;
+    rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
+    if( rc ) return rc;
+    rc = sqlitepager_write(*ppPage);
+  }
+  return rc;
+}
+
+/*
+** Add a page of the database file to the freelist.  Either pgno or
+** pPage but not both may be 0. 
+**
+** sqlitepager_unref() is NOT called for pPage.
+*/
+static int freePage(Btree *pBt, void *pPage, Pgno pgno){
+  PageOne *pPage1 = pBt->page1;
+  OverflowPage *pOvfl = (OverflowPage*)pPage;
+  int rc;
+  int needUnref = 0;
+  MemPage *pMemPage;
+
+  if( pgno==0 ){
+    assert( pOvfl!=0 );
+    pgno = sqlitepager_pagenumber(pOvfl);
+  }
+  assert( pgno>2 );
+  assert( sqlitepager_pagenumber(pOvfl)==pgno );
+  pMemPage = (MemPage*)pPage;
+  pMemPage->isInit = 0;
+  if( pMemPage->pParent ){
+    sqlitepager_unref(pMemPage->pParent);
+    pMemPage->pParent = 0;
+  }
+  rc = sqlitepager_write(pPage1);
+  if( rc ){
+    return rc;
+  }
+  SWAB_ADD(pBt, pPage1->nFree, 1);
+  if( pPage1->nFree!=0 && pPage1->freeList!=0 ){
+    OverflowPage *pFreeIdx;
+    rc = sqlitepager_get(pBt->pPager, SWAB32(pBt, pPage1->freeList),
+                        (void**)&pFreeIdx);
+    if( rc==SQLITE_OK ){
+      FreelistInfo *pInfo = (FreelistInfo*)pFreeIdx->aPayload;
+      int n = SWAB32(pBt, pInfo->nFree);
+      if( n<(sizeof(pInfo->aFree)/sizeof(pInfo->aFree[0])) ){
+        rc = sqlitepager_write(pFreeIdx);
+        if( rc==SQLITE_OK ){
+          pInfo->aFree[n] = SWAB32(pBt, pgno);
+          SWAB_ADD(pBt, pInfo->nFree, 1);
+          sqlitepager_unref(pFreeIdx);
+          sqlitepager_dont_write(pBt->pPager, pgno);
+          return rc;
+        }
+      }
+      sqlitepager_unref(pFreeIdx);
+    }
+  }
+  if( pOvfl==0 ){
+    assert( pgno>0 );
+    rc = sqlitepager_get(pBt->pPager, pgno, (void**)&pOvfl);
+    if( rc ) return rc;
+    needUnref = 1;
+  }
+  rc = sqlitepager_write(pOvfl);
+  if( rc ){
+    if( needUnref ) sqlitepager_unref(pOvfl);
+    return rc;
+  }
+  pOvfl->iNext = pPage1->freeList;
+  pPage1->freeList = SWAB32(pBt, pgno);
+  memset(pOvfl->aPayload, 0, OVERFLOW_SIZE);
+  if( needUnref ) rc = sqlitepager_unref(pOvfl);
+  return rc;
+}
+
+/*
+** Erase all the data out of a cell.  This involves returning overflow
+** pages back the freelist.
+*/
+static int clearCell(Btree *pBt, Cell *pCell){
+  Pager *pPager = pBt->pPager;
+  OverflowPage *pOvfl;
+  Pgno ovfl, nextOvfl;
+  int rc;
+
+  if( NKEY(pBt, pCell->h) + NDATA(pBt, pCell->h) <= MX_LOCAL_PAYLOAD ){
+    return SQLITE_OK;
+  }
+  ovfl = SWAB32(pBt, pCell->ovfl);
+  pCell->ovfl = 0;
+  while( ovfl ){
+    rc = sqlitepager_get(pPager, ovfl, (void**)&pOvfl);
+    if( rc ) return rc;
+    nextOvfl = SWAB32(pBt, pOvfl->iNext);
+    rc = freePage(pBt, pOvfl, ovfl);
+    if( rc ) return rc;
+    sqlitepager_unref(pOvfl);
+    ovfl = nextOvfl;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Create a new cell from key and data.  Overflow pages are allocated as
+** necessary and linked to this cell.  
+*/
+static int fillInCell(
+  Btree *pBt,              /* The whole Btree.  Needed to allocate pages */
+  Cell *pCell,             /* Populate this Cell structure */
+  const void *pKey, int nKey,    /* The key */
+  const void *pData,int nData    /* The data */
+){
+  OverflowPage *pOvfl, *pPrior;
+  Pgno *pNext;
+  int spaceLeft;
+  int n, rc;
+  int nPayload;
+  const char *pPayload;
+  char *pSpace;
+  Pgno nearby = 0;
+
+  pCell->h.leftChild = 0;
+  pCell->h.nKey = SWAB16(pBt, nKey & 0xffff);
+  pCell->h.nKeyHi = nKey >> 16;
+  pCell->h.nData = SWAB16(pBt, nData & 0xffff);
+  pCell->h.nDataHi = nData >> 16;
+  pCell->h.iNext = 0;
+
+  pNext = &pCell->ovfl;
+  pSpace = pCell->aPayload;
+  spaceLeft = MX_LOCAL_PAYLOAD;
+  pPayload = pKey;
+  pKey = 0;
+  nPayload = nKey;
+  pPrior = 0;
+  while( nPayload>0 ){
+    if( spaceLeft==0 ){
+      rc = allocatePage(pBt, (MemPage**)&pOvfl, pNext, nearby);
+      if( rc ){
+        *pNext = 0;
+      }else{
+        nearby = *pNext;
+      }
+      if( pPrior ) sqlitepager_unref(pPrior);
+      if( rc ){
+        clearCell(pBt, pCell);
+        return rc;
+      }
+      if( pBt->needSwab ) *pNext = swab32(*pNext);
+      pPrior = pOvfl;
+      spaceLeft = OVERFLOW_SIZE;
+      pSpace = pOvfl->aPayload;
+      pNext = &pOvfl->iNext;
+    }
+    n = nPayload;
+    if( n>spaceLeft ) n = spaceLeft;
+    memcpy(pSpace, pPayload, n);
+    nPayload -= n;
+    if( nPayload==0 && pData ){
+      pPayload = pData;
+      nPayload = nData;
+      pData = 0;
+    }else{
+      pPayload += n;
+    }
+    spaceLeft -= n;
+    pSpace += n;
+  }
+  *pNext = 0;
+  if( pPrior ){
+    sqlitepager_unref(pPrior);
+  }
+  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 void reparentPage(Pager *pPager, Pgno pgno, MemPage *pNewParent,int idx){
+  MemPage *pThis;
+
+  if( pgno==0 ) return;
+  assert( pPager!=0 );
+  pThis = sqlitepager_lookup(pPager, pgno);
+  if( pThis && pThis->isInit ){
+    if( pThis->pParent!=pNewParent ){
+      if( pThis->pParent ) sqlitepager_unref(pThis->pParent);
+      pThis->pParent = pNewParent;
+      if( pNewParent ) sqlitepager_ref(pNewParent);
+    }
+    pThis->idxParent = idx;
+    sqlitepager_unref(pThis);
+  }
+}
+
+/*
+** Reparent all children of the given page to be the given page.
+** 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 void reparentChildPages(Btree *pBt, MemPage *pPage){
+  int i;
+  Pager *pPager = pBt->pPager;
+  for(i=0; i<pPage->nCell; i++){
+    reparentPage(pPager, SWAB32(pBt, pPage->apCell[i]->h.leftChild), pPage, i);
+  }
+  reparentPage(pPager, SWAB32(pBt, pPage->u.hdr.rightChild), pPage, i);
+  pPage->idxShift = 0;
+}
+
+/*
+** 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.
+**
+** Do not bother maintaining the integrity of the linked list of Cells.
+** Only the pPage->apCell[] array is important.  The relinkCellList() 
+** routine will be called soon after this routine in order to rebuild 
+** the linked list.
+*/
+static void dropCell(Btree *pBt, MemPage *pPage, int idx, int sz){
+  int j;
+  assert( idx>=0 && idx<pPage->nCell );
+  assert( sz==cellSize(pBt, pPage->apCell[idx]) );
+  assert( sqlitepager_iswriteable(pPage) );
+  freeSpace(pBt, pPage, Addr(pPage->apCell[idx]) - Addr(pPage), sz);
+  for(j=idx; j<pPage->nCell-1; j++){
+    pPage->apCell[j] = pPage->apCell[j+1];
+  }
+  pPage->nCell--;
+  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 just make pPage->apCell[i] point to the content
+** and set pPage->isOverfull.  
+**
+** Do not bother maintaining the integrity of the linked list of Cells.
+** Only the pPage->apCell[] array is important.  The relinkCellList() 
+** routine will be called soon after this routine in order to rebuild 
+** the linked list.
+*/
+static void insertCell(Btree *pBt, MemPage *pPage, int i, Cell *pCell, int sz){
+  int idx, j;
+  assert( i>=0 && i<=pPage->nCell );
+  assert( sz==cellSize(pBt, pCell) );
+  assert( sqlitepager_iswriteable(pPage) );
+  idx = allocateSpace(pBt, pPage, sz);
+  for(j=pPage->nCell; j>i; j--){
+    pPage->apCell[j] = pPage->apCell[j-1];
+  }
+  pPage->nCell++;
+  if( idx<=0 ){
+    pPage->isOverfull = 1;
+    pPage->apCell[i] = pCell;
+  }else{
+    memcpy(&pPage->u.aDisk[idx], pCell, sz);
+    pPage->apCell[i] = (Cell*)&pPage->u.aDisk[idx];
+  }
+  pPage->idxShift = 1;
+}
+
+/*
+** Rebuild the linked list of cells on a page so that the cells
+** occur in the order specified by the pPage->apCell[] array.  
+** Invoke this routine once to repair damage after one or more
+** invocations of either insertCell() or dropCell().
+*/
+static void relinkCellList(Btree *pBt, MemPage *pPage){
+  int i;
+  u16 *pIdx;
+  assert( sqlitepager_iswriteable(pPage) );
+  pIdx = &pPage->u.hdr.firstCell;
+  for(i=0; i<pPage->nCell; i++){
+    int idx = Addr(pPage->apCell[i]) - Addr(pPage);
+    assert( idx>0 && idx<SQLITE_USABLE_SIZE );
+    *pIdx = SWAB16(pBt, idx);
+    pIdx = &pPage->apCell[i]->h.iNext;
+  }
+  *pIdx = 0;
+}
+
+/*
+** Make a copy of the contents of pFrom into pTo.  The pFrom->apCell[]
+** pointers that point into pFrom->u.aDisk[] must be adjusted to point
+** into pTo->u.aDisk[] instead.  But some pFrom->apCell[] entries might
+** not point to pFrom->u.aDisk[].  Those are unchanged.
+*/
+static void copyPage(MemPage *pTo, MemPage *pFrom){
+  uptr from, to;
+  int i;
+  memcpy(pTo->u.aDisk, pFrom->u.aDisk, SQLITE_USABLE_SIZE);
+  pTo->pParent = 0;
+  pTo->isInit = 1;
+  pTo->nCell = pFrom->nCell;
+  pTo->nFree = pFrom->nFree;
+  pTo->isOverfull = pFrom->isOverfull;
+  to = Addr(pTo);
+  from = Addr(pFrom);
+  for(i=0; i<pTo->nCell; i++){
+    uptr x = Addr(pFrom->apCell[i]);
+    if( x>from && x<from+SQLITE_USABLE_SIZE ){
+      *((uptr*)&pTo->apCell[i]) = x + to - from;
+    }else{
+      pTo->apCell[i] = pFrom->apCell[i];
+    }
+  }
+}
+
+/*
+** 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 */
+
+/*
+** This routine redistributes Cells on pPage and up to two siblings
+** of pPage so that all pages have about the same amount of free space.
+** Usually one sibling on either side of pPage is used in the balancing,
+** though both siblings might come from one side if pPage is the first
+** or last child of its parent.  If pPage has fewer than two 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 in an effort to keep pages between 66% and 100% full. The root page
+** is special and is allowed to be less than 66% full. 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 empty.
+**
+** This routine calls relinkCellList() on its input page regardless of
+** whether or not it does any real balancing.  Client routines will typically
+** invoke insertCell() or dropCell() before calling this routine, so we
+** need to call relinkCellList() to clean up the mess that those other
+** routines left behind.
+**
+** pCur is left pointing to the same cell as when this routine was called
+** even if that cell gets moved to a different page.  pCur may be NULL.
+** Set the pCur parameter to NULL if you do not care about keeping track
+** of a cell as that will save this routine the work of keeping track of it.
+**
+** Note that when this routine is called, some of the Cells on pPage
+** might not actually be stored in pPage->u.aDisk[].  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->u.aDisk[].
+**
+** 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(Btree *pBt, MemPage *pPage, BtCursor *pCur){
+  MemPage *pParent;            /* The parent of pPage */
+  int nCell;                   /* Number of cells in apCell[] */
+  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->apCell[] */
+  int nxDiv;                   /* Next divider slot in pParent->apCell[] */
+  int rc;                      /* The return code */
+  int iCur;                    /* apCell[iCur] is the cell of the cursor */
+  MemPage *pOldCurPage;        /* The cursor originally points to this page */
+  int subtotal;                /* Subtotal of bytes in cells on one page */
+  MemPage *extraUnref = 0;     /* A page that needs to be unref-ed */
+  MemPage *apOld[NB];          /* pPage and up to two siblings */
+  Pgno pgnoOld[NB];            /* Page numbers for each page in apOld[] */
+  MemPage *apNew[NB+1];        /* pPage and up to NB siblings after balancing */
+  Pgno pgnoNew[NB+1];          /* Page numbers for each page in apNew[] */
+  int idxDiv[NB];              /* Indices of divider cells in pParent */
+  Cell *apDiv[NB];             /* Divider cells in pParent */
+  Cell aTemp[NB];              /* Temporary holding area for apDiv[] */
+  int cntNew[NB+1];            /* Index in apCell[] of cell after i-th page */
+  int szNew[NB+1];             /* Combined size of cells place on i-th page */
+  MemPage aOld[NB];            /* Temporary copies of pPage and its siblings */
+  Cell *apCell[(MX_CELL+2)*NB]; /* All cells from pages being balanced */
+  int szCell[(MX_CELL+2)*NB];  /* Local size of all cells */
+
+  /* 
+  ** Return without doing any work if pPage is neither overfull nor
+  ** underfull.
+  */
+  assert( sqlitepager_iswriteable(pPage) );
+  if( !pPage->isOverfull && pPage->nFree<SQLITE_USABLE_SIZE/2 
+        && pPage->nCell>=2){
+    relinkCellList(pBt, pPage);
+    return SQLITE_OK;
+  }
+
+  /*
+  ** Find the parent of the page to be balanceed.
+  ** If there is no parent, it means this page is the root page and
+  ** special rules apply.
+  */
+  pParent = pPage->pParent;
+  if( pParent==0 ){
+    Pgno pgnoChild;
+    MemPage *pChild;
+    assert( pPage->isInit );
+    if( pPage->nCell==0 ){
+      if( pPage->u.hdr.rightChild ){
+        /*
+        ** The root page is empty.  Copy the one child page
+        ** into the root page and return.  This reduces the depth
+        ** of the BTree by one.
+        */
+        pgnoChild = SWAB32(pBt, pPage->u.hdr.rightChild);
+        rc = sqlitepager_get(pBt->pPager, pgnoChild, (void**)&pChild);
+        if( rc ) return rc;
+        memcpy(pPage, pChild, SQLITE_USABLE_SIZE);
+        pPage->isInit = 0;
+        rc = initPage(pBt, pPage, sqlitepager_pagenumber(pPage), 0);
+        assert( rc==SQLITE_OK );
+        reparentChildPages(pBt, pPage);
+        if( pCur && pCur->pPage==pChild ){
+          sqlitepager_unref(pChild);
+          pCur->pPage = pPage;
+          sqlitepager_ref(pPage);
+        }
+        freePage(pBt, pChild, pgnoChild);
+        sqlitepager_unref(pChild);
+      }else{
+        relinkCellList(pBt, pPage);
+      }
+      return SQLITE_OK;
+    }
+    if( !pPage->isOverfull ){
+      /* It is OK for the root page to be less than half full.
+      */
+      relinkCellList(pBt, pPage);
+      return SQLITE_OK;
+    }
+    /*
+    ** If we get to here, it means 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.  Then fall thru to the code below which will cause
+    ** the overfull child page to be split.
+    */
+    rc = sqlitepager_write(pPage);
+    if( rc ) return rc;
+    rc = allocatePage(pBt, &pChild, &pgnoChild, sqlitepager_pagenumber(pPage));
+    if( rc ) return rc;
+    assert( sqlitepager_iswriteable(pChild) );
+    copyPage(pChild, pPage);
+    pChild->pParent = pPage;
+    pChild->idxParent = 0;
+    sqlitepager_ref(pPage);
+    pChild->isOverfull = 1;
+    if( pCur && pCur->pPage==pPage ){
+      sqlitepager_unref(pPage);
+      pCur->pPage = pChild;
+    }else{
+      extraUnref = pChild;
+    }
+    zeroPage(pBt, pPage);
+    pPage->u.hdr.rightChild = SWAB32(pBt, pgnoChild);
+    pParent = pPage;
+    pPage = pChild;
+  }
+  rc = sqlitepager_write(pParent);
+  if( rc ) return rc;
+  assert( pParent->isInit );
+  
+  /*
+  ** Find the Cell in the parent page whose h.leftChild 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, swabPgno;
+    pgno = sqlitepager_pagenumber(pPage);
+    swabPgno = SWAB32(pBt, pgno);
+    for(idx=0; idx<pParent->nCell; idx++){
+      if( pParent->apCell[idx]->h.leftChild==swabPgno ){
+        break;
+      }
+    }
+    assert( idx<pParent->nCell || pParent->u.hdr.rightChild==swabPgno );
+  }else{
+    idx = pPage->idxParent;
+  }
+
+  /*
+  ** Initialize variables so that it will be safe to jump
+  ** directly to balance_cleanup at any moment.
+  */
+  nOld = nNew = 0;
+  sqlitepager_ref(pParent);
+
+  /*
+  ** 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 ){
+      idxDiv[i] = k;
+      apDiv[i] = pParent->apCell[k];
+      nDiv++;
+      pgnoOld[i] = SWAB32(pBt, apDiv[i]->h.leftChild);
+    }else if( k==pParent->nCell ){
+      pgnoOld[i] = SWAB32(pBt, pParent->u.hdr.rightChild);
+    }else{
+      break;
+    }
+    rc = sqlitepager_get(pBt->pPager, pgnoOld[i], (void**)&apOld[i]);
+    if( rc ) goto balance_cleanup;
+    rc = initPage(pBt, apOld[i], pgnoOld[i], pParent);
+    if( rc ) goto balance_cleanup;
+    apOld[i]->idxParent = k;
+    nOld++;
+  }
+
+  /*
+  ** Set iCur to be the index in apCell[] of the cell that the cursor
+  ** is pointing to.  We will need this later on in order to keep the
+  ** cursor pointing at the same cell.  If pCur points to a page that
+  ** has no involvement with this rebalancing, then set iCur to a large
+  ** number so that the iCur==j tests always fail in the main cell
+  ** distribution loop below.
+  */
+  if( pCur ){
+    iCur = 0;
+    for(i=0; i<nOld; i++){
+      if( pCur->pPage==apOld[i] ){
+        iCur += pCur->idx;
+        break;
+      }
+      iCur += apOld[i]->nCell;
+      if( i<nOld-1 && pCur->pPage==pParent && pCur->idx==idxDiv[i] ){
+        break;
+      }
+      iCur++;
+    }
+    pOldCurPage = pCur->pPage;
+  }
+
+  /*
+  ** 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++){
+    copyPage(&aOld[i], apOld[i]);
+  }
+
+  /*
+  ** Load pointers to all cells on sibling pages and the divider cells
+  ** into the local apCell[] array.  Make copies of the divider cells
+  ** into aTemp[] and remove the the divider Cells from pParent.
+  */
+  nCell = 0;
+  for(i=0; i<nOld; i++){
+    MemPage *pOld = &aOld[i];
+    for(j=0; j<pOld->nCell; j++){
+      apCell[nCell] = pOld->apCell[j];
+      szCell[nCell] = cellSize(pBt, apCell[nCell]);
+      nCell++;
+    }
+    if( i<nOld-1 ){
+      szCell[nCell] = cellSize(pBt, apDiv[i]);
+      memcpy(&aTemp[i], apDiv[i], szCell[nCell]);
+      apCell[nCell] = &aTemp[i];
+      dropCell(pBt, pParent, nxDiv, szCell[nCell]);
+      assert( SWAB32(pBt, apCell[nCell]->h.leftChild)==pgnoOld[i] );
+      apCell[nCell]->h.leftChild = pOld->u.hdr.rightChild;
+      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 path i from path i+1.  
+  ** cntNew[k] should equal nCell.
+  **
+  ** This little patch of code is critical for keeping the tree
+  ** balanced. 
+  */
+  for(subtotal=k=i=0; i<nCell; i++){
+    subtotal += szCell[i];
+    if( subtotal > USABLE_SPACE ){
+      szNew[k] = subtotal - szCell[i];
+      cntNew[k] = i;
+      subtotal = 0;
+      k++;
+    }
+  }
+  szNew[k] = subtotal;
+  cntNew[k] = nCell;
+  k++;
+  for(i=k-1; i>0; i--){
+    while( szNew[i]<USABLE_SPACE/2 ){
+      cntNew[i-1]--;
+      assert( cntNew[i-1]>0 );
+      szNew[i] += szCell[cntNew[i-1]];
+      szNew[i-1] -= szCell[cntNew[i-1]-1];
+    }
+  }
+  assert( cntNew[0]>0 );
+
+  /*
+  ** Allocate k new pages.  Reuse old pages where possible.
+  */
+  for(i=0; i<k; i++){
+    if( i<nOld ){
+      apNew[i] = apOld[i];
+      pgnoNew[i] = pgnoOld[i];
+      apOld[i] = 0;
+      sqlitepager_write(apNew[i]);
+    }else{
+      rc = allocatePage(pBt, &apNew[i], &pgnoNew[i], pgnoNew[i-1]);
+      if( rc ) goto balance_cleanup;
+    }
+    nNew++;
+    zeroPage(pBt, apNew[i]);
+    apNew[i]->isInit = 1;
+  }
+
+  /* Free any old pages that were not reused as new pages.
+  */
+  while( i<nOld ){
+    rc = freePage(pBt, apOld[i], pgnoOld[i]);
+    if( rc ) goto balance_cleanup;
+    sqlitepager_unref(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;
+    }
+  }
+
+  /*
+  ** 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++){
+    MemPage *pNew = apNew[i];
+    while( j<cntNew[i] ){
+      assert( pNew->nFree>=szCell[j] );
+      if( pCur && iCur==j ){ pCur->pPage = pNew; pCur->idx = pNew->nCell; }
+      insertCell(pBt, pNew, pNew->nCell, apCell[j], szCell[j]);
+      j++;
+    }
+    assert( pNew->nCell>0 );
+    assert( !pNew->isOverfull );
+    relinkCellList(pBt, pNew);
+    if( i<nNew-1 && j<nCell ){
+      pNew->u.hdr.rightChild = apCell[j]->h.leftChild;
+      apCell[j]->h.leftChild = SWAB32(pBt, pgnoNew[i]);
+      if( pCur && iCur==j ){ pCur->pPage = pParent; pCur->idx = nxDiv; }
+      insertCell(pBt, pParent, nxDiv, apCell[j], szCell[j]);
+      j++;
+      nxDiv++;
+    }
+  }
+  assert( j==nCell );
+  apNew[nNew-1]->u.hdr.rightChild = aOld[nOld-1].u.hdr.rightChild;
+  if( nxDiv==pParent->nCell ){
+    pParent->u.hdr.rightChild = SWAB32(pBt, pgnoNew[nNew-1]);
+  }else{
+    pParent->apCell[nxDiv]->h.leftChild = SWAB32(pBt, pgnoNew[nNew-1]);
+  }
+  if( pCur ){
+    if( j<=iCur && pCur->pPage==pParent && pCur->idx>idxDiv[nOld-1] ){
+      assert( pCur->pPage==pOldCurPage );
+      pCur->idx += nNew - nOld;
+    }else{
+      assert( pOldCurPage!=0 );
+      sqlitepager_ref(pCur->pPage);
+      sqlitepager_unref(pOldCurPage);
+    }
+  }
+
+  /*
+  ** Reparent children of all cells.
+  */
+  for(i=0; i<nNew; i++){
+    reparentChildPages(pBt, apNew[i]);
+  }
+  reparentChildPages(pBt, pParent);
+
+  /*
+  ** balance the parent page.
+  */
+  rc = balance(pBt, pParent, pCur);
+
+  /*
+  ** Cleanup before returning.
+  */
+balance_cleanup:
+  if( extraUnref ){
+    sqlitepager_unref(extraUnref);
+  }
+  for(i=0; i<nOld; i++){
+    if( apOld[i]!=0 && apOld[i]!=&aOld[i] ) sqlitepager_unref(apOld[i]);
+  }
+  for(i=0; i<nNew; i++){
+    sqlitepager_unref(apNew[i]);
+  }
+  if( pCur && pCur->pPage==0 ){
+    pCur->pPage = pParent;
+    pCur->idx = 0;
+  }else{
+    sqlitepager_unref(pParent);
+  }
+  return rc;
+}
+
+/*
+** This routine checks all cursors that point to the same table
+** as pCur points to.  If any of those cursors were opened with
+** wrFlag==0 then this routine returns SQLITE_LOCKED.  If all
+** cursors point to the same table were opened with wrFlag==1
+** then this routine returns SQLITE_OK.
+**
+** In addition to checking for read-locks (where a read-lock 
+** means a cursor opened with wrFlag==0) this routine also moves
+** all cursors other than pCur so that they are pointing to the 
+** first Cell on 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(BtCursor *pCur){
+  BtCursor *p;
+  assert( pCur->wrFlag );
+  for(p=pCur->pShared; p!=pCur; p=p->pShared){
+    assert( p );
+    assert( p->pgnoRoot==pCur->pgnoRoot );
+    if( p->wrFlag==0 ) return SQLITE_LOCKED;
+    if( sqlitepager_pagenumber(p->pPage)!=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 database the record should be inserted into.  The cursor
+** is left pointing at the new record.
+*/
+static int fileBtreeInsert(
+  BtCursor *pCur,                /* Insert data into the table of this cursor */
+  const void *pKey, int nKey,    /* The key of the new record */
+  const void *pData, int nData   /* The data of the new record */
+){
+  Cell newCell;
+  int rc;
+  int loc;
+  int szNew;
+  MemPage *pPage;
+  Btree *pBt = pCur->pBt;
+
+  if( pCur->pPage==0 ){
+    return SQLITE_ABORT;  /* A rollback destroyed this cursor */
+  }
+  if( !pBt->inTrans || nKey+nData==0 ){
+    /* Must start a transaction before doing an insert */
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  assert( !pBt->readOnly );
+  if( !pCur->wrFlag ){
+    return SQLITE_PERM;   /* Cursor not open for writing */
+  }
+  if( checkReadLocks(pCur) ){
+    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
+  }
+  rc = fileBtreeMoveto(pCur, pKey, nKey, &loc);
+  if( rc ) return rc;
+  pPage = pCur->pPage;
+  assert( pPage->isInit );
+  rc = sqlitepager_write(pPage);
+  if( rc ) return rc;
+  rc = fillInCell(pBt, &newCell, pKey, nKey, pData, nData);
+  if( rc ) return rc;
+  szNew = cellSize(pBt, &newCell);
+  if( loc==0 ){
+    newCell.h.leftChild = pPage->apCell[pCur->idx]->h.leftChild;
+    rc = clearCell(pBt, pPage->apCell[pCur->idx]);
+    if( rc ) return rc;
+    dropCell(pBt, pPage, pCur->idx, cellSize(pBt, pPage->apCell[pCur->idx]));
+  }else if( loc<0 && pPage->nCell>0 ){
+    assert( pPage->u.hdr.rightChild==0 );  /* Must be a leaf page */
+    pCur->idx++;
+  }else{
+    assert( pPage->u.hdr.rightChild==0 );  /* Must be a leaf page */
+  }
+  insertCell(pBt, pPage, pCur->idx, &newCell, szNew);
+  rc = balance(pCur->pBt, pPage, pCur);
+  /* sqliteBtreePageDump(pCur->pBt, pCur->pgnoRoot, 1); */
+  /* fflush(stdout); */
+  pCur->eSkip = SKIP_INVALID;
+  return rc;
+}
+
+/*
+** Delete the entry that the cursor is pointing to.
+**
+** The cursor is left pointing at either the next or the previous
+** entry.  If the cursor is left pointing to the next entry, then 
+** the pCur->eSkip flag is set to SKIP_NEXT which forces the next call to 
+** sqliteBtreeNext() to be a no-op.  That way, you can always call
+** sqliteBtreeNext() after a delete and the cursor will be left
+** pointing to the first entry after the deleted entry.  Similarly,
+** pCur->eSkip is set to SKIP_PREV is the cursor is left pointing to
+** the entry prior to the deleted entry so that a subsequent call to
+** sqliteBtreePrevious() will always leave the cursor pointing at the
+** entry immediately before the one that was deleted.
+*/
+static int fileBtreeDelete(BtCursor *pCur){
+  MemPage *pPage = pCur->pPage;
+  Cell *pCell;
+  int rc;
+  Pgno pgnoChild;
+  Btree *pBt = pCur->pBt;
+
+  assert( pPage->isInit );
+  if( pCur->pPage==0 ){
+    return SQLITE_ABORT;  /* A rollback destroyed this cursor */
+  }
+  if( !pBt->inTrans ){
+    /* Must start a transaction before doing a delete */
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  assert( !pBt->readOnly );
+  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) ){
+    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
+  }
+  rc = sqlitepager_write(pPage);
+  if( rc ) return rc;
+  pCell = pPage->apCell[pCur->idx];
+  pgnoChild = SWAB32(pBt, pCell->h.leftChild);
+  clearCell(pBt, pCell);
+  if( pgnoChild ){
+    /*
+    ** 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;
+    Cell *pNext;
+    int szNext;
+    int notUsed;
+    getTempCursor(pCur, &leafCur);
+    rc = fileBtreeNext(&leafCur, &notUsed);
+    if( rc!=SQLITE_OK ){
+      if( rc!=SQLITE_NOMEM ) rc = SQLITE_CORRUPT;
+      return rc;
+    }
+    rc = sqlitepager_write(leafCur.pPage);
+    if( rc ) return rc;
+    dropCell(pBt, pPage, pCur->idx, cellSize(pBt, pCell));
+    pNext = leafCur.pPage->apCell[leafCur.idx];
+    szNext = cellSize(pBt, pNext);
+    pNext->h.leftChild = SWAB32(pBt, pgnoChild);
+    insertCell(pBt, pPage, pCur->idx, pNext, szNext);
+    rc = balance(pBt, pPage, pCur);
+    if( rc ) return rc;
+    pCur->eSkip = SKIP_NEXT;
+    dropCell(pBt, leafCur.pPage, leafCur.idx, szNext);
+    rc = balance(pBt, leafCur.pPage, pCur);
+    releaseTempCursor(&leafCur);
+  }else{
+    dropCell(pBt, pPage, pCur->idx, cellSize(pBt, pCell));
+    if( pCur->idx>=pPage->nCell ){
+      pCur->idx = pPage->nCell-1;
+      if( pCur->idx<0 ){ 
+        pCur->idx = 0;
+        pCur->eSkip = SKIP_NEXT;
+      }else{
+        pCur->eSkip = SKIP_PREV;
+      }
+    }else{
+      pCur->eSkip = SKIP_NEXT;
+    }
+    rc = balance(pBt, pPage, pCur);
+  }
+  return rc;
+}
+
+/*
+** Create a new BTree table.  Write into *piTable the page
+** number for the root page of the new table.
+**
+** In the current implementation, BTree tables and BTree indices are the 
+** the same.  In the future, we may change this so that BTree tables
+** are restricted to having a 4-byte integer key and arbitrary data and
+** BTree indices are restricted to having an arbitrary key and no data.
+** But for now, this routine also serves to create indices.
+*/
+static int fileBtreeCreateTable(Btree *pBt, int *piTable){
+  MemPage *pRoot;
+  Pgno pgnoRoot;
+  int rc;
+  if( !pBt->inTrans ){
+    /* Must start a transaction first */
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  if( pBt->readOnly ){
+    return SQLITE_READONLY;
+  }
+  rc = allocatePage(pBt, &pRoot, &pgnoRoot, 0);
+  if( rc ) return rc;
+  assert( sqlitepager_iswriteable(pRoot) );
+  zeroPage(pBt, pRoot);
+  sqlitepager_unref(pRoot);
+  *piTable = (int)pgnoRoot;
+  return SQLITE_OK;
+}
+
+/*
+** Erase the given database page and all its children.  Return
+** the page to the freelist.
+*/
+static int clearDatabasePage(Btree *pBt, Pgno pgno, int freePageFlag){
+  MemPage *pPage;
+  int rc;
+  Cell *pCell;
+  int idx;
+
+  rc = sqlitepager_get(pBt->pPager, pgno, (void**)&pPage);
+  if( rc ) return rc;
+  rc = sqlitepager_write(pPage);
+  if( rc ) return rc;
+  rc = initPage(pBt, pPage, pgno, 0);
+  if( rc ) return rc;
+  idx = SWAB16(pBt, pPage->u.hdr.firstCell);
+  while( idx>0 ){
+    pCell = (Cell*)&pPage->u.aDisk[idx];
+    idx = SWAB16(pBt, pCell->h.iNext);
+    if( pCell->h.leftChild ){
+      rc = clearDatabasePage(pBt, SWAB32(pBt, pCell->h.leftChild), 1);
+      if( rc ) return rc;
+    }
+    rc = clearCell(pBt, pCell);
+    if( rc ) return rc;
+  }
+  if( pPage->u.hdr.rightChild ){
+    rc = clearDatabasePage(pBt, SWAB32(pBt, pPage->u.hdr.rightChild), 1);
+    if( rc ) return rc;
+  }
+  if( freePageFlag ){
+    rc = freePage(pBt, pPage, pgno);
+  }else{
+    zeroPage(pBt, pPage);
+  }
+  sqlitepager_unref(pPage);
+  return rc;
+}
+
+/*
+** Delete all information from a single table in the database.
+*/
+static int fileBtreeClearTable(Btree *pBt, int iTable){
+  int rc;
+  BtCursor *pCur;
+  if( !pBt->inTrans ){
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
+    if( pCur->pgnoRoot==(Pgno)iTable ){
+      if( pCur->wrFlag==0 ) return SQLITE_LOCKED;
+      moveToRoot(pCur);
+    }
+  }
+  rc = clearDatabasePage(pBt, (Pgno)iTable, 0);
+  if( rc ){
+    fileBtreeRollback(pBt);
+  }
+  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 2) is never added to the freelist.
+*/
+static int fileBtreeDropTable(Btree *pBt, int iTable){
+  int rc;
+  MemPage *pPage;
+  BtCursor *pCur;
+  if( !pBt->inTrans ){
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
+    if( pCur->pgnoRoot==(Pgno)iTable ){
+      return SQLITE_LOCKED;  /* Cannot drop a table that has a cursor */
+    }
+  }
+  rc = sqlitepager_get(pBt->pPager, (Pgno)iTable, (void**)&pPage);
+  if( rc ) return rc;
+  rc = fileBtreeClearTable(pBt, iTable);
+  if( rc ) return rc;
+  if( iTable>2 ){
+    rc = freePage(pBt, pPage, iTable);
+  }else{
+    zeroPage(pBt, pPage);
+  }
+  sqlitepager_unref(pPage);
+  return rc;  
+}
+
+#if 0 /* UNTESTED */
+/*
+** Copy all cell data from one database file into another.
+** pages back the freelist.
+*/
+static int copyCell(Btree *pBtFrom, BTree *pBtTo, Cell *pCell){
+  Pager *pFromPager = pBtFrom->pPager;
+  OverflowPage *pOvfl;
+  Pgno ovfl, nextOvfl;
+  Pgno *pPrev;
+  int rc = SQLITE_OK;
+  MemPage *pNew, *pPrevPg;
+  Pgno new;
+
+  if( NKEY(pBtTo, pCell->h) + NDATA(pBtTo, pCell->h) <= MX_LOCAL_PAYLOAD ){
+    return SQLITE_OK;
+  }
+  pPrev = &pCell->ovfl;
+  pPrevPg = 0;
+  ovfl = SWAB32(pBtTo, pCell->ovfl);
+  while( ovfl && rc==SQLITE_OK ){
+    rc = sqlitepager_get(pFromPager, ovfl, (void**)&pOvfl);
+    if( rc ) return rc;
+    nextOvfl = SWAB32(pBtFrom, pOvfl->iNext);
+    rc = allocatePage(pBtTo, &pNew, &new, 0);
+    if( rc==SQLITE_OK ){
+      rc = sqlitepager_write(pNew);
+      if( rc==SQLITE_OK ){
+        memcpy(pNew, pOvfl, SQLITE_USABLE_SIZE);
+        *pPrev = SWAB32(pBtTo, new);
+        if( pPrevPg ){
+          sqlitepager_unref(pPrevPg);
+        }
+        pPrev = &pOvfl->iNext;
+        pPrevPg = pNew;
+      }
+    }
+    sqlitepager_unref(pOvfl);
+    ovfl = nextOvfl;
+  }
+  if( pPrevPg ){
+    sqlitepager_unref(pPrevPg);
+  }
+  return rc;
+}
+#endif
+
+
+#if 0 /* UNTESTED */
+/*
+** Copy a page of data from one database over to another.
+*/
+static int copyDatabasePage(
+  Btree *pBtFrom,
+  Pgno pgnoFrom,
+  Btree *pBtTo,
+  Pgno *pTo
+){
+  MemPage *pPageFrom, *pPage;
+  Pgno to;
+  int rc;
+  Cell *pCell;
+  int idx;
+
+  rc = sqlitepager_get(pBtFrom->pPager, pgno, (void**)&pPageFrom);
+  if( rc ) return rc;
+  rc = allocatePage(pBt, &pPage, pTo, 0);
+  if( rc==SQLITE_OK ){
+    rc = sqlitepager_write(pPage);
+  }
+  if( rc==SQLITE_OK ){
+    memcpy(pPage, pPageFrom, SQLITE_USABLE_SIZE);
+    idx = SWAB16(pBt, pPage->u.hdr.firstCell);
+    while( idx>0 ){
+      pCell = (Cell*)&pPage->u.aDisk[idx];
+      idx = SWAB16(pBt, pCell->h.iNext);
+      if( pCell->h.leftChild ){
+        Pgno newChld;
+        rc = copyDatabasePage(pBtFrom, SWAB32(pBtFrom, pCell->h.leftChild),
+                              pBtTo, &newChld);
+        if( rc ) return rc;
+        pCell->h.leftChild = SWAB32(pBtFrom, newChld);
+      }
+      rc = copyCell(pBtFrom, pBtTo, pCell);
+      if( rc ) return rc;
+    }
+    if( pPage->u.hdr.rightChild ){
+      Pgno newChld;
+      rc = copyDatabasePage(pBtFrom, SWAB32(pBtFrom, pPage->u.hdr.rightChild), 
+                            pBtTo, &newChld);
+      if( rc ) return rc;
+      pPage->u.hdr.rightChild = SWAB32(pBtTo, newChild);
+    }
+  }
+  sqlitepager_unref(pPage);
+  return rc;
+}
+#endif
+
+/*
+** Read the meta-information out of a database file.
+*/
+static int fileBtreeGetMeta(Btree *pBt, int *aMeta){
+  PageOne *pP1;
+  int rc;
+  int i;
+
+  rc = sqlitepager_get(pBt->pPager, 1, (void**)&pP1);
+  if( rc ) return rc;
+  aMeta[0] = SWAB32(pBt, pP1->nFree);
+  for(i=0; i<sizeof(pP1->aMeta)/sizeof(pP1->aMeta[0]); i++){
+    aMeta[i+1] = SWAB32(pBt, pP1->aMeta[i]);
+  }
+  sqlitepager_unref(pP1);
+  return SQLITE_OK;
+}
+
+/*
+** Write meta-information back into the database.
+*/
+static int fileBtreeUpdateMeta(Btree *pBt, int *aMeta){
+  PageOne *pP1;
+  int rc, i;
+  if( !pBt->inTrans ){
+    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
+  }
+  pP1 = pBt->page1;
+  rc = sqlitepager_write(pP1);
+  if( rc ) return rc;   
+  for(i=0; i<sizeof(pP1->aMeta)/sizeof(pP1->aMeta[0]); i++){
+    pP1->aMeta[i] = SWAB32(pBt, aMeta[i+1]);
+  }
+  return SQLITE_OK;
+}
+
+/******************************************************************************
+** The complete implementation of the BTree subsystem is above this line.
+** All the code the follows is for testing and troubleshooting the BTree
+** subsystem.  None of the code that follows is used during normal operation.
+******************************************************************************/
+
+/*
+** Print a disassembly of the given page on standard output.  This routine
+** is used for debugging and testing only.
+*/
+#ifdef SQLITE_TEST
+static int fileBtreePageDump(Btree *pBt, int pgno, int recursive){
+  int rc;
+  MemPage *pPage;
+  int i, j;
+  int nFree;
+  u16 idx;
+  char range[20];
+  unsigned char payload[20];
+  rc = sqlitepager_get(pBt->pPager, (Pgno)pgno, (void**)&pPage);
+  if( rc ){
+    return rc;
+  }
+  if( recursive ) printf("PAGE %d:\n", pgno);
+  i = 0;
+  idx = SWAB16(pBt, pPage->u.hdr.firstCell);
+  while( idx>0 && idx<=SQLITE_USABLE_SIZE-MIN_CELL_SIZE ){
+    Cell *pCell = (Cell*)&pPage->u.aDisk[idx];
+    int sz = cellSize(pBt, pCell);
+    sprintf(range,"%d..%d", idx, idx+sz-1);
+    sz = NKEY(pBt, pCell->h) + NDATA(pBt, pCell->h);
+    if( sz>sizeof(payload)-1 ) sz = sizeof(payload)-1;
+    memcpy(payload, pCell->aPayload, sz);
+    for(j=0; j<sz; j++){
+      if( payload[j]<0x20 || payload[j]>0x7f ) payload[j] = '.';
+    }
+    payload[sz] = 0;
+    printf(
+      "cell %2d: i=%-10s chld=%-4d nk=%-4d nd=%-4d payload=%s\n",
+      i, range, (int)pCell->h.leftChild, 
+      NKEY(pBt, pCell->h), NDATA(pBt, pCell->h),
+      payload
+    );
+    if( pPage->isInit && pPage->apCell[i]!=pCell ){
+      printf("**** apCell[%d] does not match on prior entry ****\n", i);
+    }
+    i++;
+    idx = SWAB16(pBt, pCell->h.iNext);
+  }
+  if( idx!=0 ){
+    printf("ERROR: next cell index out of range: %d\n", idx);
+  }
+  printf("right_child: %d\n", SWAB32(pBt, pPage->u.hdr.rightChild));
+  nFree = 0;
+  i = 0;
+  idx = SWAB16(pBt, pPage->u.hdr.firstFree);
+  while( idx>0 && idx<SQLITE_USABLE_SIZE ){
+    FreeBlk *p = (FreeBlk*)&pPage->u.aDisk[idx];
+    sprintf(range,"%d..%d", idx, idx+p->iSize-1);
+    nFree += SWAB16(pBt, p->iSize);
+    printf("freeblock %2d: i=%-10s size=%-4d total=%d\n",
+       i, range, SWAB16(pBt, p->iSize), nFree);
+    idx = SWAB16(pBt, p->iNext);
+    i++;
+  }
+  if( idx!=0 ){
+    printf("ERROR: next freeblock index out of range: %d\n", idx);
+  }
+  if( recursive && pPage->u.hdr.rightChild!=0 ){
+    idx = SWAB16(pBt, pPage->u.hdr.firstCell);
+    while( idx>0 && idx<SQLITE_USABLE_SIZE-MIN_CELL_SIZE ){
+      Cell *pCell = (Cell*)&pPage->u.aDisk[idx];
+      fileBtreePageDump(pBt, SWAB32(pBt, pCell->h.leftChild), 1);
+      idx = SWAB16(pBt, pCell->h.iNext);
+    }
+    fileBtreePageDump(pBt, SWAB32(pBt, pPage->u.hdr.rightChild), 1);
+  }
+  sqlitepager_unref(pPage);
+  return SQLITE_OK;
+}
+#endif
+
+#ifdef SQLITE_TEST
+/*
+** Fill aResult[] with information about the entry and page that the
+** cursor is pointing to.
+** 
+**   aResult[0] =  The page number
+**   aResult[1] =  The entry number
+**   aResult[2] =  Total number of entries on this page
+**   aResult[3] =  Size of this entry
+**   aResult[4] =  Number of free bytes on this page
+**   aResult[5] =  Number of free blocks on the page
+**   aResult[6] =  Page number of the left child of this entry
+**   aResult[7] =  Page number of the right child for the whole page
+**
+** This routine is used for testing and debugging only.
+*/
+static int fileBtreeCursorDump(BtCursor *pCur, int *aResult){
+  int cnt, idx;
+  MemPage *pPage = pCur->pPage;
+  Btree *pBt = pCur->pBt;
+  aResult[0] = sqlitepager_pagenumber(pPage);
+  aResult[1] = pCur->idx;
+  aResult[2] = pPage->nCell;
+  if( pCur->idx>=0 && pCur->idx<pPage->nCell ){
+    aResult[3] = cellSize(pBt, pPage->apCell[pCur->idx]);
+    aResult[6] = SWAB32(pBt, pPage->apCell[pCur->idx]->h.leftChild);
+  }else{
+    aResult[3] = 0;
+    aResult[6] = 0;
+  }
+  aResult[4] = pPage->nFree;
+  cnt = 0;
+  idx = SWAB16(pBt, pPage->u.hdr.firstFree);
+  while( idx>0 && idx<SQLITE_USABLE_SIZE ){
+    cnt++;
+    idx = SWAB16(pBt, ((FreeBlk*)&pPage->u.aDisk[idx])->iNext);
+  }
+  aResult[5] = cnt;
+  aResult[7] = SWAB32(pBt, pPage->u.hdr.rightChild);
+  return SQLITE_OK;
+}
+#endif
+
+/*
+** Return the pager associated with a BTree.  This routine is used for
+** testing and debugging only.
+*/
+static Pager *fileBtreePager(Btree *pBt){
+  return pBt->pPager;
+}
+
+/*
+** This structure is passed around through all the sanity checking routines
+** in order to keep track of some global state information.
+*/
+typedef struct IntegrityCk IntegrityCk;
+struct IntegrityCk {
+  Btree *pBt;    /* The tree being checked out */
+  Pager *pPager; /* The associated pager.  Also accessible by pBt->pPager */
+  int nPage;     /* Number of pages in the database */
+  int *anRef;    /* Number of times each page is referenced */
+  char *zErrMsg; /* An error message.  NULL of no errors seen. */
+};
+
+/*
+** Append a message to the error message string.
+*/
+static void checkAppendMsg(IntegrityCk *pCheck, char *zMsg1, char *zMsg2){
+  if( pCheck->zErrMsg ){
+    char *zOld = pCheck->zErrMsg;
+    pCheck->zErrMsg = 0;
+    sqliteSetString(&pCheck->zErrMsg, zOld, "\n", zMsg1, zMsg2, (char*)0);
+    sqliteFree(zOld);
+  }else{
+    sqliteSetString(&pCheck->zErrMsg, zMsg1, zMsg2, (char*)0);
+  }
+}
+
+/*
+** 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 ){
+    char zBuf[100];
+    sprintf(zBuf, "invalid page number %d", iPage);
+    checkAppendMsg(pCheck, zContext, zBuf);
+    return 1;
+  }
+  if( pCheck->anRef[iPage]==1 ){
+    char zBuf[100];
+    sprintf(zBuf, "2nd reference to page %d", iPage);
+    checkAppendMsg(pCheck, zContext, zBuf);
+    return 1;
+  }
+  return  (pCheck->anRef[iPage]++)>1;
+}
+
+/*
+** 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;
+  char zMsg[100];
+  while( N-- > 0 ){
+    OverflowPage *pOvfl;
+    if( iPage<1 ){
+      sprintf(zMsg, "%d pages missing from overflow list", N+1);
+      checkAppendMsg(pCheck, zContext, zMsg);
+      break;
+    }
+    if( checkRef(pCheck, iPage, zContext) ) break;
+    if( sqlitepager_get(pCheck->pPager, (Pgno)iPage, (void**)&pOvfl) ){
+      sprintf(zMsg, "failed to get page %d", iPage);
+      checkAppendMsg(pCheck, zContext, zMsg);
+      break;
+    }
+    if( isFreeList ){
+      FreelistInfo *pInfo = (FreelistInfo*)pOvfl->aPayload;
+      int n = SWAB32(pCheck->pBt, pInfo->nFree);
+      for(i=0; i<n; i++){
+        checkRef(pCheck, SWAB32(pCheck->pBt, pInfo->aFree[i]), zContext);
+      }
+      N -= n;
+    }
+    iPage = SWAB32(pCheck->pBt, pOvfl->iNext);
+    sqlitepager_unref(pOvfl);
+  }
+}
+
+/*
+** Return negative if zKey1<zKey2.
+** Return zero if zKey1==zKey2.
+** Return positive if zKey1>zKey2.
+*/
+static int keyCompare(
+  const char *zKey1, int nKey1,
+  const char *zKey2, int nKey2
+){
+  int min = nKey1>nKey2 ? nKey2 : nKey1;
+  int c = memcmp(zKey1, zKey2, min);
+  if( c==0 ){
+    c = nKey1 - nKey2;
+  }
+  return c;
+}
+
+/*
+** 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.
+**      2.  Make sure cell keys are in order.
+**      3.  Make sure no key is less than or equal to zLowerBound.
+**      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 */
+  char *zLowerBound,    /* All keys should be greater than this, if not NULL */
+  int nLower,           /* Number of characters in zLowerBound */
+  char *zUpperBound,    /* All keys should be less than this, if not NULL */
+  int nUpper            /* Number of characters in zUpperBound */
+){
+  MemPage *pPage;
+  int i, rc, depth, d2, pgno;
+  char *zKey1, *zKey2;
+  int nKey1, nKey2;
+  BtCursor cur;
+  Btree *pBt;
+  char zMsg[100];
+  char zContext[100];
+  char hit[SQLITE_USABLE_SIZE];
+
+  /* Check that the page exists
+  */
+  cur.pBt = pBt = pCheck->pBt;
+  if( iPage==0 ) return 0;
+  if( checkRef(pCheck, iPage, zParentContext) ) return 0;
+  sprintf(zContext, "On tree page %d: ", iPage);
+  if( (rc = sqlitepager_get(pCheck->pPager, (Pgno)iPage, (void**)&pPage))!=0 ){
+    sprintf(zMsg, "unable to get the page. error code=%d", rc);
+    checkAppendMsg(pCheck, zContext, zMsg);
+    return 0;
+  }
+  if( (rc = initPage(pBt, pPage, (Pgno)iPage, pParent))!=0 ){
+    sprintf(zMsg, "initPage() returns error code %d", rc);
+    checkAppendMsg(pCheck, zContext, zMsg);
+    sqlitepager_unref(pPage);
+    return 0;
+  }
+
+  /* Check out all the cells.
+  */
+  depth = 0;
+  if( zLowerBound ){
+    zKey1 = sqliteMalloc( nLower+1 );
+    memcpy(zKey1, zLowerBound, nLower);
+    zKey1[nLower] = 0;
+  }else{
+    zKey1 = 0;
+  }
+  nKey1 = nLower;
+  cur.pPage = pPage;
+  for(i=0; i<pPage->nCell; i++){
+    Cell *pCell = pPage->apCell[i];
+    int sz;
+
+    /* Check payload overflow pages
+    */
+    nKey2 = NKEY(pBt, pCell->h);
+    sz = nKey2 + NDATA(pBt, pCell->h);
+    sprintf(zContext, "On page %d cell %d: ", iPage, i);
+    if( sz>MX_LOCAL_PAYLOAD ){
+      int nPage = (sz - MX_LOCAL_PAYLOAD + OVERFLOW_SIZE - 1)/OVERFLOW_SIZE;
+      checkList(pCheck, 0, SWAB32(pBt, pCell->ovfl), nPage, zContext);
+    }
+
+    /* Check that keys are in the right order
+    */
+    cur.idx = i;
+    zKey2 = sqliteMallocRaw( nKey2+1 );
+    getPayload(&cur, 0, nKey2, zKey2);
+    if( zKey1 && keyCompare(zKey1, nKey1, zKey2, nKey2)>=0 ){
+      checkAppendMsg(pCheck, zContext, "Key is out of order");
+    }
+
+    /* Check sanity of left child page.
+    */
+    pgno = SWAB32(pBt, pCell->h.leftChild);
+    d2 = checkTreePage(pCheck, pgno, pPage, zContext, zKey1,nKey1,zKey2,nKey2);
+    if( i>0 && d2!=depth ){
+      checkAppendMsg(pCheck, zContext, "Child page depth differs");
+    }
+    depth = d2;
+    sqliteFree(zKey1);
+    zKey1 = zKey2;
+    nKey1 = nKey2;
+  }
+  pgno = SWAB32(pBt, pPage->u.hdr.rightChild);
+  sprintf(zContext, "On page %d at right child: ", iPage);
+  checkTreePage(pCheck, pgno, pPage, zContext, zKey1,nKey1,zUpperBound,nUpper);
+  sqliteFree(zKey1);
+ 
+  /* Check for complete coverage of the page
+  */
+  memset(hit, 0, sizeof(hit));
+  memset(hit, 1, sizeof(PageHdr));
+  for(i=SWAB16(pBt, pPage->u.hdr.firstCell); i>0 && i<SQLITE_USABLE_SIZE; ){
+    Cell *pCell = (Cell*)&pPage->u.aDisk[i];
+    int j;
+    for(j=i+cellSize(pBt, pCell)-1; j>=i; j--) hit[j]++;
+    i = SWAB16(pBt, pCell->h.iNext);
+  }
+  for(i=SWAB16(pBt,pPage->u.hdr.firstFree); i>0 && i<SQLITE_USABLE_SIZE; ){
+    FreeBlk *pFBlk = (FreeBlk*)&pPage->u.aDisk[i];
+    int j;
+    for(j=i+SWAB16(pBt,pFBlk->iSize)-1; j>=i; j--) hit[j]++;
+    i = SWAB16(pBt,pFBlk->iNext);
+  }
+  for(i=0; i<SQLITE_USABLE_SIZE; i++){
+    if( hit[i]==0 ){
+      sprintf(zMsg, "Unused space at byte %d of page %d", i, iPage);
+      checkAppendMsg(pCheck, zMsg, 0);
+      break;
+    }else if( hit[i]>1 ){
+      sprintf(zMsg, "Multiple uses for byte %d of page %d", i, iPage);
+      checkAppendMsg(pCheck, zMsg, 0);
+      break;
+    }
+  }
+
+  /* Check that free space is kept to a minimum
+  */
+#if 0
+  if( pParent && pParent->nCell>2 && pPage->nFree>3*SQLITE_USABLE_SIZE/4 ){
+    sprintf(zMsg, "free space (%d) greater than max (%d)", pPage->nFree,
+       SQLITE_USABLE_SIZE/3);
+    checkAppendMsg(pCheck, zContext, zMsg);
+  }
+#endif
+
+  sqlitepager_unref(pPage);
+  return depth;
+}
+
+/*
+** 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 *fileBtreeIntegrityCheck(Btree *pBt, int *aRoot, int nRoot){
+  int i;
+  int nRef;
+  IntegrityCk sCheck;
+
+  nRef = *sqlitepager_stats(pBt->pPager);
+  if( lockBtree(pBt)!=SQLITE_OK ){
+    return sqliteStrDup("Unable to actquire a read lock on the database");
+  }
+  sCheck.pBt = pBt;
+  sCheck.pPager = pBt->pPager;
+  sCheck.nPage = sqlitepager_pagecount(sCheck.pPager);
+  if( sCheck.nPage==0 ){
+    unlockBtreeIfUnused(pBt);
+    return 0;
+  }
+  sCheck.anRef = sqliteMallocRaw( (sCheck.nPage+1)*sizeof(sCheck.anRef[0]) );
+  sCheck.anRef[1] = 1;
+  for(i=2; i<=sCheck.nPage; i++){ sCheck.anRef[i] = 0; }
+  sCheck.zErrMsg = 0;
+
+  /* Check the integrity of the freelist
+  */
+  checkList(&sCheck, 1, SWAB32(pBt, pBt->page1->freeList),
+            SWAB32(pBt, pBt->page1->nFree), "Main freelist: ");
+
+  /* Check all the tables.
+  */
+  for(i=0; i<nRoot; i++){
+    if( aRoot[i]==0 ) continue;
+    checkTreePage(&sCheck, aRoot[i], 0, "List of tree roots: ", 0,0,0,0);
+  }
+
+  /* Make sure every page in the file is referenced
+  */
+  for(i=1; i<=sCheck.nPage; i++){
+    if( sCheck.anRef[i]==0 ){
+      char zBuf[100];
+      sprintf(zBuf, "Page %d is never used", i);
+      checkAppendMsg(&sCheck, zBuf, 0);
+    }
+  }
+
+  /* Make sure this analysis did not leave any unref() pages
+  */
+  unlockBtreeIfUnused(pBt);
+  if( nRef != *sqlitepager_stats(pBt->pPager) ){
+    char zBuf[100];
+    sprintf(zBuf, 
+      "Outstanding page count goes from %d to %d during this analysis",
+      nRef, *sqlitepager_stats(pBt->pPager)
+    );
+    checkAppendMsg(&sCheck, zBuf, 0);
+  }
+
+  /* Clean  up and report errors.
+  */
+  sqliteFree(sCheck.anRef);
+  return sCheck.zErrMsg;
+}
+
+/*
+** Return the full pathname of the underlying database file.
+*/
+static const char *fileBtreeGetFilename(Btree *pBt){
+  assert( pBt->pPager!=0 );
+  return sqlitepager_filename(pBt->pPager);
+}
+
+/*
+** 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 fileBtreeCopyFile(Btree *pBtTo, Btree *pBtFrom){
+  int rc = SQLITE_OK;
+  Pgno i, nPage, nToPage;
+
+  if( !pBtTo->inTrans || !pBtFrom->inTrans ) return SQLITE_ERROR;
+  if( pBtTo->needSwab!=pBtFrom->needSwab ) return SQLITE_ERROR;
+  if( pBtTo->pCursor ) return SQLITE_BUSY;
+  memcpy(pBtTo->page1, pBtFrom->page1, SQLITE_USABLE_SIZE);
+  rc = sqlitepager_overwrite(pBtTo->pPager, 1, pBtFrom->page1);
+  nToPage = sqlitepager_pagecount(pBtTo->pPager);
+  nPage = sqlitepager_pagecount(pBtFrom->pPager);
+  for(i=2; rc==SQLITE_OK && i<=nPage; i++){
+    void *pPage;
+    rc = sqlitepager_get(pBtFrom->pPager, i, &pPage);
+    if( rc ) break;
+    rc = sqlitepager_overwrite(pBtTo->pPager, i, pPage);
+    if( rc ) break;
+    sqlitepager_unref(pPage);
+  }
+  for(i=nPage+1; rc==SQLITE_OK && i<=nToPage; i++){
+    void *pPage;
+    rc = sqlitepager_get(pBtTo->pPager, i, &pPage);
+    if( rc ) break;
+    rc = sqlitepager_write(pPage);
+    sqlitepager_unref(pPage);
+    sqlitepager_dont_write(pBtTo->pPager, i);
+  }
+  if( !rc && nPage<nToPage ){
+    rc = sqlitepager_truncate(pBtTo->pPager, nPage);
+  }
+  if( rc ){
+    fileBtreeRollback(pBtTo);
+  }
+  return rc;  
+}
+
+/*
+** The following tables contain pointers to all of the interface
+** routines for this implementation of the B*Tree backend.  To
+** substitute a different implemention of the backend, one has merely
+** to provide pointers to alternative functions in similar tables.
+*/
+static BtOps sqliteBtreeOps = {
+    fileBtreeClose,
+    fileBtreeSetCacheSize,
+    fileBtreeSetSafetyLevel,
+    fileBtreeBeginTrans,
+    fileBtreeCommit,
+    fileBtreeRollback,
+    fileBtreeBeginCkpt,
+    fileBtreeCommitCkpt,
+    fileBtreeRollbackCkpt,
+    fileBtreeCreateTable,
+    fileBtreeCreateTable,  /* Really sqliteBtreeCreateIndex() */
+    fileBtreeDropTable,
+    fileBtreeClearTable,
+    fileBtreeCursor,
+    fileBtreeGetMeta,
+    fileBtreeUpdateMeta,
+    fileBtreeIntegrityCheck,
+    fileBtreeGetFilename,
+    fileBtreeCopyFile,
+    fileBtreePager,
+#ifdef SQLITE_TEST
+    fileBtreePageDump,
+#endif
+};
+static BtCursorOps sqliteBtreeCursorOps = {
+    fileBtreeMoveto,
+    fileBtreeDelete,
+    fileBtreeInsert,
+    fileBtreeFirst,
+    fileBtreeLast,
+    fileBtreeNext,
+    fileBtreePrevious,
+    fileBtreeKeySize,
+    fileBtreeKey,
+    fileBtreeKeyCompare,
+    fileBtreeDataSize,
+    fileBtreeData,
+    fileBtreeCloseCursor,
+#ifdef SQLITE_TEST
+    fileBtreeCursorDump,
+#endif
+};