SQLite

  if( pFree ){
    sqlite3PageFree(pFree);
  }
  return rc;
}

/* Overwrite content from pX into pDest.  Only do the write if the
** content is different from what is already there.
*/
static int btreeOverwriteContent(
  MemPage *pPage,           /* MemPage on which writing will occur */
  u8 *pDest,                /* Pointer to the place to start writing */
  const BtreePayload *pX,   /* Source of data to write */
  int iOffset,              /* Offset of first byte to write */
  int iAmt                  /* Number of bytes to be written */
){
  int nData = pX->nData - iOffset;
  if( nData<=0 ){
    /* Overwritting with zeros */
    int i;
    for(i=0; i<iAmt && pDest[i]==0; i++){}
    if( i<iAmt ){
      int rc = sqlite3PagerWrite(pPage->pDbPage);
      if( rc ) return rc;
      memset(pDest + i, 0, iAmt - i);
    }
  }else{
    if( nData<iAmt ){
      /* Mixed read data and zeros at the end.  Make a recursive call
      ** to write the zeros then fall through to write the real data */
      btreeOverwriteContent(pPage, pDest+nData, pX, iOffset+nData, iAmt-nData);
      iAmt = nData;
    }
    if( memcmp(pDest, ((u8*)pX->pData) + iOffset, iAmt)!=0 ){
      int rc = sqlite3PagerWrite(pPage->pDbPage);
      if( rc ) return rc;
      memcpy(pDest, ((u8*)pX->pData) + iOffset, iAmt);
    }
  }
  return SQLITE_OK;
}

/*
** Overwrite the cell that cursor pCur is pointing to with fresh content
** contained in pX.
*/
static int btreeOverwriteCell(BtCursor *pCur, const BtreePayload *pX){
  int iOffset;                        /* Next byte of pX->pData to write */
  int nTotal = pX->nData + pX->nZero; /* Total bytes of to write */
  int rc;                             /* Return code */
  MemPage *pPage = pCur->pPage;       /* Page being written */
  BtShared *pBt;                      /* Btree */
  Pgno ovflPgno;                      /* Next overflow page to write */
  u32 ovflPageSize;                   /* Size to write on overflow page */

  /* Overwrite the local portion first */
  rc = btreeOverwriteContent(pPage, pCur->info.pPayload, pX,
                             0, pCur->info.nLocal);
  if( rc ) return rc;
  if( pCur->info.nLocal==nTotal ) return SQLITE_OK;

  /* Now overwrite the overflow pages */
  iOffset = pCur->info.nLocal;
  ovflPgno = get4byte(pCur->info.pPayload + iOffset);
  pBt = pPage->pBt;
  ovflPageSize = pBt->usableSize - 4;
  do{
    rc = btreeGetPage(pBt, ovflPgno, &pPage, 0);
    if( rc ) return rc;
    if( iOffset+ovflPageSize>nTotal ){
      ovflPgno = get4byte(pPage->aData + ovflPageSize);
    }else{
      ovflPageSize = nTotal - iOffset;
    }
    rc = btreeOverwriteContent(pPage, pPage->aData, pX,
                               iOffset, ovflPageSize);
    if( rc ) return rc;
    iOffset += ovflPageSize;
    sqlite3PagerUnref(pPage->pDbPage);
  }while( iOffset<nTotal );
  return SQLITE_OK;    
}


/*
** Insert a new record into the BTree.  The content of the new record
** is described by the pX object.  The pCur cursor is used only to
** define what table the record should be inserted into, and is left
** pointing at a random location.
**

    assert( (flags & BTREE_SAVEPOSITION)==0 || 
            ((pCur->curFlags&BTCF_ValidNKey)!=0 && pX->nKey==pCur->info.nKey) );

    /* If the cursor is currently on the last row and we are appending a
    ** new row onto the end, set the "loc" to avoid an unnecessary
    ** btreeMoveto() call */
    if( (pCur->curFlags&BTCF_ValidNKey)!=0 && pX->nKey==pCur->info.nKey ){
      /* The current is currently pointing to the entry that is to be
      ** overwritten */
      if( pCur->info.nPayload==pX->nData+pX->nZero ){
        return btreeOverwriteCell(pCur, pX);
      }
      loc = 0;
    }else if( loc==0 ){
      rc = sqlite3BtreeMovetoUnpacked(pCur, 0, pX->nKey, flags!=0, &loc);
      if( rc ) return rc;
    }
  }else if( loc==0 && (flags & BTREE_SAVEPOSITION)==0 ){
    if( pX->nMem ){