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Overview
Comment:In sqlite3BtreeInsert() when replacing a re-existing row, try to overwrite the cell directly rather than deallocate and reallocate the cell.
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SHA1:0b86fbca6615ccf1f3a62614db577a8acbec6d9e
User & Date: drh 2016-12-09 17:32:51
References
2017-06-08
11:07 New ticket [fda22108] Corrupt due to REPLACE in an auto-vacuumed database. artifact: 548c43a8 user: drh
2016-12-27
12:45
Adjust a corruption test case to accommodate the sqlite3BtreeInsert() optimization of check-in [0b86fbca66]. check-in: 4cb0945f user: drh tags: trunk
Context
2016-12-09
18:09
Additional comments and an assert on the sqlite3BtreeInsert() overwrite optimization. check-in: c1f0ae9d user: drh tags: trunk
17:32
In sqlite3BtreeInsert() when replacing a re-existing row, try to overwrite the cell directly rather than deallocate and reallocate the cell. check-in: 0b86fbca user: drh tags: trunk
16:12
Fix an fts5 bug that could cause a crash following an OOM error or sqlite3_interrupt() interrupt. check-in: 0ea3ece9 user: dan tags: trunk
Changes
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Changes to src/btree.c.

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** Free any overflow pages associated with the given Cell.  Write the
** local Cell size (the number of bytes on the original page, omitting
** overflow) into *pnSize.
*/
static int clearCell(
  MemPage *pPage,          /* The page that contains the Cell */
  unsigned char *pCell,    /* First byte of the Cell */
  u16 *pnSize              /* Write the size of the Cell here */
){
  BtShared *pBt = pPage->pBt;
  CellInfo info;
  Pgno ovflPgno;
  int rc;
  int nOvfl;
  u32 ovflPageSize;

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  pPage->xParseCell(pPage, pCell, &info);
  *pnSize = info.nSize;
  if( info.nLocal==info.nPayload ){
    return SQLITE_OK;  /* No overflow pages. Return without doing anything */
  }
  if( pCell+info.nSize-1 > pPage->aData+pPage->maskPage ){
    return SQLITE_CORRUPT_BKPT;  /* Cell extends past end of page */
  }
  ovflPgno = get4byte(pCell + info.nSize - 4);
  assert( pBt->usableSize > 4 );
  ovflPageSize = pBt->usableSize - 4;
  nOvfl = (info.nPayload - info.nLocal + ovflPageSize - 1)/ovflPageSize;
  assert( nOvfl>0 || 
    (CORRUPT_DB && (info.nPayload + ovflPageSize)<ovflPageSize)
  );
  while( nOvfl-- ){
    Pgno iNext = 0;
    MemPage *pOvfl = 0;
    if( ovflPgno<2 || ovflPgno>btreePagecount(pBt) ){
      /* 0 is not a legal page number and page 1 cannot be an 
      ** overflow page. Therefore if ovflPgno<2 or past the end of the 
................................................................................
  assert( newCell!=0 );
  rc = fillInCell(pPage, newCell, pX, &szNew);
  if( rc ) goto end_insert;
  assert( szNew==pPage->xCellSize(pPage, newCell) );
  assert( szNew <= MX_CELL_SIZE(pBt) );
  idx = pCur->aiIdx[pCur->iPage];
  if( loc==0 ){
    u16 szOld;
    assert( idx<pPage->nCell );
    rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc ){
      goto end_insert;
    }
    oldCell = findCell(pPage, idx);
    if( !pPage->leaf ){
      memcpy(newCell, oldCell, 4);
    }
    rc = clearCell(pPage, oldCell, &szOld);





    dropCell(pPage, idx, szOld, &rc);
    if( rc ) goto end_insert;
  }else if( loc<0 && pPage->nCell>0 ){
    assert( pPage->leaf );
    idx = ++pCur->aiIdx[pCur->iPage];
  }else{
    assert( pPage->leaf );
  }
................................................................................
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;              
  int rc;                              /* Return code */
  MemPage *pPage;                      /* Page to delete cell from */
  unsigned char *pCell;                /* Pointer to cell to delete */
  int iCellIdx;                        /* Index of cell to delete */
  int iCellDepth;                      /* Depth of node containing pCell */ 
  u16 szCell;                          /* Size of the cell being deleted */
  int bSkipnext = 0;                   /* Leaf cursor in SKIPNEXT state */
  u8 bPreserve = flags & BTREE_SAVEPOSITION;  /* Keep cursor valid */

  assert( cursorOwnsBtShared(pCur) );
  assert( pBt->inTransaction==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( pCur->curFlags & BTCF_WriteFlag );
................................................................................
  }

  /* Make the page containing the entry to be deleted writable. Then free any
  ** overflow pages associated with the entry and finally remove the cell
  ** itself from within the page.  */
  rc = sqlite3PagerWrite(pPage->pDbPage);
  if( rc ) return rc;
  rc = clearCell(pPage, pCell, &szCell);
  dropCell(pPage, iCellIdx, szCell, &rc);
  if( rc ) return rc;

  /* If the cell deleted was not located on a leaf page, then the cursor
  ** is currently pointing to the largest entry in the sub-tree headed
  ** by the child-page of the cell that was just deleted from an internal
  ** node. The cell from the leaf node needs to be moved to the internal
  ** node to replace the deleted cell.  */
................................................................................
  int *pnChange            /* Add number of Cells freed to this counter */
){
  MemPage *pPage;
  int rc;
  unsigned char *pCell;
  int i;
  int hdr;
  u16 szCell;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno>btreePagecount(pBt) ){
    return SQLITE_CORRUPT_BKPT;
  }
  rc = getAndInitPage(pBt, pgno, &pPage, 0, 0);
  if( rc ) return rc;
................................................................................
  hdr = pPage->hdrOffset;
  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
    if( !pPage->leaf ){
      rc = clearDatabasePage(pBt, get4byte(pCell), 1, pnChange);
      if( rc ) goto cleardatabasepage_out;
    }
    rc = clearCell(pPage, pCell, &szCell);
    if( rc ) goto cleardatabasepage_out;
  }
  if( !pPage->leaf ){
    rc = clearDatabasePage(pBt, get4byte(&pPage->aData[hdr+8]), 1, pnChange);
    if( rc ) goto cleardatabasepage_out;
  }else if( pnChange ){
    assert( pPage->intKey || CORRUPT_DB );







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** Free any overflow pages associated with the given Cell.  Write the
** local Cell size (the number of bytes on the original page, omitting
** overflow) into *pnSize.
*/
static int clearCell(
  MemPage *pPage,          /* The page that contains the Cell */
  unsigned char *pCell,    /* First byte of the Cell */
  CellInfo *pInfo          /* Size information about the cell */
){
  BtShared *pBt = pPage->pBt;

  Pgno ovflPgno;
  int rc;
  int nOvfl;
  u32 ovflPageSize;

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  pPage->xParseCell(pPage, pCell, pInfo);
  if( pInfo->nLocal==pInfo->nPayload ){

    return SQLITE_OK;  /* No overflow pages. Return without doing anything */
  }
  if( pCell+pInfo->nSize-1 > pPage->aData+pPage->maskPage ){
    return SQLITE_CORRUPT_BKPT;  /* Cell extends past end of page */
  }
  ovflPgno = get4byte(pCell + pInfo->nSize - 4);
  assert( pBt->usableSize > 4 );
  ovflPageSize = pBt->usableSize - 4;
  nOvfl = (pInfo->nPayload - pInfo->nLocal + ovflPageSize - 1)/ovflPageSize;
  assert( nOvfl>0 || 
    (CORRUPT_DB && (pInfo->nPayload + ovflPageSize)<ovflPageSize)
  );
  while( nOvfl-- ){
    Pgno iNext = 0;
    MemPage *pOvfl = 0;
    if( ovflPgno<2 || ovflPgno>btreePagecount(pBt) ){
      /* 0 is not a legal page number and page 1 cannot be an 
      ** overflow page. Therefore if ovflPgno<2 or past the end of the 
................................................................................
  assert( newCell!=0 );
  rc = fillInCell(pPage, newCell, pX, &szNew);
  if( rc ) goto end_insert;
  assert( szNew==pPage->xCellSize(pPage, newCell) );
  assert( szNew <= MX_CELL_SIZE(pBt) );
  idx = pCur->aiIdx[pCur->iPage];
  if( loc==0 ){
    CellInfo info;
    assert( idx<pPage->nCell );
    rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc ){
      goto end_insert;
    }
    oldCell = findCell(pPage, idx);
    if( !pPage->leaf ){
      memcpy(newCell, oldCell, 4);
    }
    rc = clearCell(pPage, oldCell, &info);
    if( info.nSize==szNew && info.nLocal==info.nPayload ){
      /* Overwrite the old cell with the new */
      memcpy(oldCell, newCell, szNew);
      return SQLITE_OK;
    }
    dropCell(pPage, idx, info.nSize, &rc);
    if( rc ) goto end_insert;
  }else if( loc<0 && pPage->nCell>0 ){
    assert( pPage->leaf );
    idx = ++pCur->aiIdx[pCur->iPage];
  }else{
    assert( pPage->leaf );
  }
................................................................................
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;              
  int rc;                              /* Return code */
  MemPage *pPage;                      /* Page to delete cell from */
  unsigned char *pCell;                /* Pointer to cell to delete */
  int iCellIdx;                        /* Index of cell to delete */
  int iCellDepth;                      /* Depth of node containing pCell */ 
  CellInfo info;                       /* Size of the cell being deleted */
  int bSkipnext = 0;                   /* Leaf cursor in SKIPNEXT state */
  u8 bPreserve = flags & BTREE_SAVEPOSITION;  /* Keep cursor valid */

  assert( cursorOwnsBtShared(pCur) );
  assert( pBt->inTransaction==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( pCur->curFlags & BTCF_WriteFlag );
................................................................................
  }

  /* Make the page containing the entry to be deleted writable. Then free any
  ** overflow pages associated with the entry and finally remove the cell
  ** itself from within the page.  */
  rc = sqlite3PagerWrite(pPage->pDbPage);
  if( rc ) return rc;
  rc = clearCell(pPage, pCell, &info);
  dropCell(pPage, iCellIdx, info.nSize, &rc);
  if( rc ) return rc;

  /* If the cell deleted was not located on a leaf page, then the cursor
  ** is currently pointing to the largest entry in the sub-tree headed
  ** by the child-page of the cell that was just deleted from an internal
  ** node. The cell from the leaf node needs to be moved to the internal
  ** node to replace the deleted cell.  */
................................................................................
  int *pnChange            /* Add number of Cells freed to this counter */
){
  MemPage *pPage;
  int rc;
  unsigned char *pCell;
  int i;
  int hdr;
  CellInfo info;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno>btreePagecount(pBt) ){
    return SQLITE_CORRUPT_BKPT;
  }
  rc = getAndInitPage(pBt, pgno, &pPage, 0, 0);
  if( rc ) return rc;
................................................................................
  hdr = pPage->hdrOffset;
  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
    if( !pPage->leaf ){
      rc = clearDatabasePage(pBt, get4byte(pCell), 1, pnChange);
      if( rc ) goto cleardatabasepage_out;
    }
    rc = clearCell(pPage, pCell, &info);
    if( rc ) goto cleardatabasepage_out;
  }
  if( !pPage->leaf ){
    rc = clearDatabasePage(pBt, get4byte(&pPage->aData[hdr+8]), 1, pnChange);
    if( rc ) goto cleardatabasepage_out;
  }else if( pnChange ){
    assert( pPage->intKey || CORRUPT_DB );