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Overview
Comment:Modify various routines inside btree.c to take a pointer to the return-code as a parameter and to no-op if the return-code storage location already contains a non-zero code. (CVS 6911)
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SHA1: 7dcf2a78727ce448d9d26bd6e2e23b553456ec54
User & Date: drh 2009-07-20 17:11:50
Context
2009-07-20
19:30
Reverse the order of two conditionals in a test in order to achieve coverage of them both. Also: clarifications to comments in btree.c. (CVS 6912) check-in: a159e9d2 user: drh tags: trunk
17:11
Modify various routines inside btree.c to take a pointer to the return-code as a parameter and to no-op if the return-code storage location already contains a non-zero code. (CVS 6911) check-in: 7dcf2a78 user: drh tags: trunk
12:33
Use an ALWAYS() on a conditional in btmutex.c that is always true. (CVS 6910) check-in: 609022ca user: drh tags: trunk
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Changes to src/btree.c.

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** 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 1.691 2009/07/16 18:21:18 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
}

/*
** Write an entry into the pointer map.
**
** This routine updates the pointer map entry for page number 'key'
** so that it maps to type 'eType' and parent page number 'pgno'.
** An error code is returned if something goes wrong, otherwise SQLITE_OK.



*/
static int ptrmapPut(BtShared *pBt, Pgno key, u8 eType, Pgno parent){
  DbPage *pDbPage;  /* The pointer map page */
  u8 *pPtrmap;      /* The pointer map data */
  Pgno iPtrmap;     /* The pointer map page number */
  int offset;       /* Offset in pointer map page */
  int rc;



  assert( sqlite3_mutex_held(pBt->mutex) );
  /* The master-journal page number must never be used as a pointer map page */
  assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );

  assert( pBt->autoVacuum );
  if( key==0 ){
    return SQLITE_CORRUPT_BKPT;

  }
  iPtrmap = PTRMAP_PAGENO(pBt, key);
  rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
  if( rc!=SQLITE_OK ){

    return rc;
  }
  offset = PTRMAP_PTROFFSET(iPtrmap, key);
  if( offset<0 ){
    rc = SQLITE_CORRUPT_BKPT;
    goto ptrmap_exit;
  }
  pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);

  if( eType!=pPtrmap[offset] || get4byte(&pPtrmap[offset+1])!=parent ){
    TRACE(("PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent));
    rc = sqlite3PagerWrite(pDbPage);
    if( rc==SQLITE_OK ){
      pPtrmap[offset] = eType;
      put4byte(&pPtrmap[offset+1], parent);
    }
  }

ptrmap_exit:
  sqlite3PagerUnref(pDbPage);
  return rc;
}

/*
** Read an entry from the pointer map.
**
** This routine retrieves the pointer map entry for page 'key', writing
** the type and parent page number to *pEType and *pPgno respectively.
................................................................................

  sqlite3PagerUnref(pDbPage);
  if( *pEType<1 || *pEType>5 ) return SQLITE_CORRUPT_BKPT;
  return SQLITE_OK;
}

#else /* if defined SQLITE_OMIT_AUTOVACUUM */
  #define ptrmapPut(w,x,y,z) SQLITE_OK
  #define ptrmapGet(w,x,y,z) SQLITE_OK
  #define ptrmapPutOvflPtr(x, y) SQLITE_OK
#endif

/*
** Given a btree page and a cell index (0 means the first cell on
** the page, 1 means the second cell, and so forth) return a pointer
** to the cell content.
**
................................................................................

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** If the cell pCell, part of page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
static int ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell){
  CellInfo info;

  assert( pCell!=0 );
  btreeParseCellPtr(pPage, pCell, &info);
  assert( (info.nData+(pPage->intKey?0:info.nKey))==info.nPayload );
  if( info.iOverflow ){
    Pgno ovfl = get4byte(&pCell[info.iOverflow]);
    return ptrmapPut(pPage->pBt, ovfl, PTRMAP_OVERFLOW1, pPage->pgno);
  }
  return SQLITE_OK;
}
#endif


/*
** Defragment the page given.  All Cells are moved to the
** end of the page and all free space is collected into one
................................................................................
    goto set_child_ptrmaps_out;
  }
  nCell = pPage->nCell;

  for(i=0; i<nCell; i++){
    u8 *pCell = findCell(pPage, i);

    rc = ptrmapPutOvflPtr(pPage, pCell);
    if( rc!=SQLITE_OK ){
      goto set_child_ptrmaps_out;
    }

    if( !pPage->leaf ){
      Pgno childPgno = get4byte(pCell);
      rc = ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno);
      if( rc!=SQLITE_OK ) goto set_child_ptrmaps_out;
    }
  }

  if( !pPage->leaf ){
    Pgno childPgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    rc = ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno);
  }

set_child_ptrmaps_out:
  pPage->isInit = isInitOrig;
  return rc;
}

................................................................................
    rc = setChildPtrmaps(pDbPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }else{
    Pgno nextOvfl = get4byte(pDbPage->aData);
    if( nextOvfl!=0 ){
      rc = ptrmapPut(pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
................................................................................
    if( rc!=SQLITE_OK ){
      releasePage(pPtrPage);
      return rc;
    }
    rc = modifyPagePointer(pPtrPage, iDbPage, iFreePage, eType);
    releasePage(pPtrPage);
    if( rc==SQLITE_OK ){
      rc = ptrmapPut(pBt, iFreePage, eType, iPtrPage);
    }
  }
  return rc;
}

/* Forward declaration required by incrVacuumStep(). */
static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);
................................................................................
  memset(pPage->aData, 0, pPage->pBt->pageSize);
#endif

  /* If the database supports auto-vacuum, write an entry in the pointer-map
  ** to indicate that the page is free.
  */
  if( ISAUTOVACUUM ){
    rc = ptrmapPut(pBt, iPage, PTRMAP_FREEPAGE, 0);
    if( rc ) goto freepage_out;
  }

  /* Now manipulate the actual database free-list structure. There are two
  ** possibilities. If the free-list is currently empty, or if the first
  ** trunk page in the free-list is full, then this page will become a
  ** new free-list trunk page. Otherwise, it will become a leaf of the
................................................................................
      ** to the pointer-map. If we write nothing to this pointer-map slot,
      ** then the optimistic overflow chain processing in clearCell()
      ** may misinterpret the uninitialised values and delete the
      ** wrong pages from the database.
      */
      if( pBt->autoVacuum && rc==SQLITE_OK ){
        u8 eType = (pgnoPtrmap?PTRMAP_OVERFLOW2:PTRMAP_OVERFLOW1);
        rc = ptrmapPut(pBt, pgnoOvfl, eType, pgnoPtrmap);
        if( rc ){
          releasePage(pOvfl);
        }
      }
#endif
      if( rc ){
        releasePage(pToRelease);
................................................................................
** Remove the i-th cell from pPage.  This routine effects pPage only.
** The cell content is not freed or deallocated.  It is assumed that
** the cell content has been copied someplace else.  This routine just
** removes the reference to the cell from pPage.
**
** "sz" must be the number of bytes in the cell.
*/
static int dropCell(MemPage *pPage, int idx, int sz){
  int i;          /* Loop counter */
  int pc;         /* Offset to cell content of cell being deleted */
  u8 *data;       /* pPage->aData */
  u8 *ptr;        /* Used to move bytes around within data[] */
  int rc;         /* The return code */



  assert( idx>=0 && idx<pPage->nCell );
  assert( sz==cellSize(pPage, idx) );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  data = pPage->aData;
  ptr = &data[pPage->cellOffset + 2*idx];
  pc = get2byte(ptr);
  if( (pc<pPage->hdrOffset+6+pPage->childPtrSize)
     || (pc+sz>pPage->pBt->usableSize) ){
    return SQLITE_CORRUPT_BKPT;

  }
  rc = freeSpace(pPage, pc, sz);
  if( rc!=SQLITE_OK ){

    return rc;
  }
  for(i=idx+1; i<pPage->nCell; i++, ptr+=2){
    ptr[0] = ptr[2];
    ptr[1] = ptr[3];
  }
  pPage->nCell--;
  put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
  pPage->nFree += 2;
  return SQLITE_OK;
}

/*
** 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
................................................................................
** pPage->nOverflow is incremented.
**
** If nSkip is non-zero, then do not copy the first nSkip bytes of the
** cell. The caller will overwrite them after this function returns. If
** nSkip is non-zero, then pCell may not point to an invalid memory location 
** (but pCell+nSkip is always valid).
*/
static int insertCell(
  MemPage *pPage,   /* Page into which we are copying */
  int i,            /* New cell becomes the i-th cell of the page */
  u8 *pCell,        /* Content of the new cell */
  int sz,           /* Bytes of content in pCell */
  u8 *pTemp,        /* Temp storage space for pCell, if needed */
  Pgno iChild       /* If non-zero, replace first 4 bytes with this value */

){
  int idx;          /* Where to write new cell content in data[] */
  int j;            /* Loop counter */
  int end;          /* First byte past the last cell pointer in data[] */
  int ins;          /* Index in data[] where new cell pointer is inserted */
  int cellOffset;   /* Address of first cell pointer in data[] */
  u8 *data;         /* The content of the whole page */
  u8 *ptr;          /* Used for moving information around in data[] */

  int nSkip = (iChild ? 4 : 0);



  assert( i>=0 && i<=pPage->nCell+pPage->nOverflow );
  assert( pPage->nCell<=MX_CELL(pPage->pBt) && MX_CELL(pPage->pBt)<=5460 );
  assert( pPage->nOverflow<=ArraySize(pPage->aOvfl) );
  assert( sz==cellSizePtr(pPage, pCell) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  if( pPage->nOverflow || sz+2>pPage->nFree ){
................................................................................
    j = pPage->nOverflow++;
    assert( j<(int)(sizeof(pPage->aOvfl)/sizeof(pPage->aOvfl[0])) );
    pPage->aOvfl[j].pCell = pCell;
    pPage->aOvfl[j].idx = (u16)i;
  }else{
    int rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc!=SQLITE_OK ){

      return rc;
    }
    assert( sqlite3PagerIswriteable(pPage->pDbPage) );
    data = pPage->aData;
    cellOffset = pPage->cellOffset;
    end = cellOffset + 2*pPage->nCell;
    ins = cellOffset + 2*i;
    rc = allocateSpace(pPage, sz, &idx);
    if( rc ) return rc;
    assert( idx>=end+2 );
    if( idx+sz > pPage->pBt->usableSize ){
      return SQLITE_CORRUPT_BKPT;

    }
    pPage->nCell++;
    pPage->nFree -= (u16)(2 + sz);
    memcpy(&data[idx+nSkip], pCell+nSkip, sz-nSkip);
    if( iChild ){
      put4byte(&data[idx], iChild);
    }
................................................................................
    put2byte(&data[ins], idx);
    put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pPage->pBt->autoVacuum ){
      /* The cell may contain a pointer to an overflow page. If so, write
      ** the entry for the overflow page into the pointer map.
      */
      return ptrmapPutOvflPtr(pPage, pCell);
    }
#endif
  }

  return SQLITE_OK;
}

/*
** Add a list of cells to a page.  The page should be initially empty.
** The cells are guaranteed to fit on the page.
*/
static void assemblePage(
................................................................................
    ** operations fails, the return code is set, but the contents
    ** of the parent page are still manipulated by thh code below.
    ** That is Ok, at this point the parent page is guaranteed to
    ** be marked as dirty. Returning an error code will cause a
    ** rollback, undoing any changes made to the parent page.
    */
    if( ISAUTOVACUUM ){
      rc = ptrmapPut(pBt, pgnoNew, PTRMAP_BTREE, pParent->pgno);
      if( szCell>pNew->minLocal && rc==SQLITE_OK ){
        rc = ptrmapPutOvflPtr(pNew, pCell);
      }
    }
  
    /* Create a divider cell to insert into pParent. The divider cell
    ** consists of a 4-byte page number (the page number of pPage) and
    ** a variable length key value (which must be the same value as the
    ** largest key on pPage).
................................................................................
    pCell = findCell(pPage, pPage->nCell-1);
    pStop = &pCell[9];
    while( (*(pCell++)&0x80) && pCell<pStop );
    pStop = &pCell[9];
    while( ((*(pOut++) = *(pCell++))&0x80) && pCell<pStop );

    /* Insert the new divider cell into pParent. */
    insertCell(pParent,pParent->nCell,pSpace,(int)(pOut-pSpace),0,pPage->pgno);


    /* Set the right-child pointer of pParent to point to the new page. */
    put4byte(&pParent->aData[pParent->hdrOffset+8], pgnoNew);
  
    /* Release the reference to the new page. */
    releasePage(pNew);
  }
................................................................................
      ** In this case, temporarily copy the cell into the aOvflSpace[]
      ** buffer. It will be copied out again as soon as the aSpace[] buffer
      ** is allocated.  */
#ifdef SQLITE_SECURE_DELETE
      memcpy(&aOvflSpace[apDiv[i]-pParent->aData], apDiv[i], szNew[i]);
      apDiv[i] = &aOvflSpace[apDiv[i]-pParent->aData];
#endif
      dropCell(pParent, i+nxDiv-pParent->nOverflow, szNew[i]);
    }
  }

  /* Make nMaxCells a multiple of 4 in order to preserve 8-byte
  ** alignment */
  nMaxCells = (nMaxCells + 3)&~3;

................................................................................
      rc = allocateBtreePage(pBt, &pNew, &pgno, pgno, 0);
      if( rc ) goto balance_cleanup;
      apNew[i] = pNew;
      nNew++;

      /* Set the pointer-map entry for the new sibling page. */
      if( ISAUTOVACUUM ){
        rc = ptrmapPut(pBt, pNew->pgno, PTRMAP_BTREE, pParent->pgno);
        if( rc!=SQLITE_OK ){
          goto balance_cleanup;
        }
      }
    }
  }

................................................................................
          assert(leafCorrection==4);
          sz = cellSizePtr(pParent, pCell);
        }
      }
      iOvflSpace += sz;
      assert( sz<=pBt->pageSize/4 );
      assert( iOvflSpace<=pBt->pageSize );
      rc = insertCell(pParent, nxDiv, pCell, sz, pTemp, pNew->pgno);
      if( rc!=SQLITE_OK ) goto balance_cleanup;
      assert( sqlite3PagerIswriteable(pParent->pDbPage) );

      j++;
      nxDiv++;
    }
  }
................................................................................

      /* If the cell was originally divider cell (and is not now) or
      ** an overflow cell, or if the cell was located on a different sibling
      ** page before the balancing, then the pointer map entries associated
      ** with any child or overflow pages need to be updated.  */
      if( isDivider || pOld->pgno!=pNew->pgno ){
        if( !leafCorrection ){
          rc = ptrmapPut(pBt, get4byte(apCell[i]), PTRMAP_BTREE, pNew->pgno);
        }
        if( szCell[i]>pNew->minLocal && rc==SQLITE_OK ){
          rc = ptrmapPutOvflPtr(pNew, apCell[i]);
        }
      }
    }

    if( !leafCorrection ){
      for(i=0; rc==SQLITE_OK && i<nNew; i++){
        rc = ptrmapPut(
	    pBt, get4byte(&apNew[i]->aData[8]), PTRMAP_BTREE, apNew[i]->pgno);
      }
    }

#if 0
    /* The ptrmapCheckPages() contains assert() statements that verify that
    ** all pointer map pages are set correctly. This is helpful while 
    ** debugging. This is usually disabled because a corrupt database may
................................................................................
  assert( pRoot->nOverflow>0 );
  assert( sqlite3_mutex_held(pBt->mutex) );

  /* Make pRoot, the root page of the b-tree, writable. Allocate a new 
  ** page that will become the new right-child of pPage. Copy the contents
  ** of the node stored on pRoot into the new child page.
  */
  if( SQLITE_OK!=(rc = sqlite3PagerWrite(pRoot->pDbPage))

   || SQLITE_OK!=(rc = allocateBtreePage(pBt,&pChild,&pgnoChild,pRoot->pgno,0))

   || SQLITE_OK!=(rc = copyNodeContent(pRoot, pChild))
   || (ISAUTOVACUUM && 
       SQLITE_OK!=(rc = ptrmapPut(pBt, pgnoChild, PTRMAP_BTREE, pRoot->pgno)))



  ){
    *ppChild = 0;
    releasePage(pChild);
    return rc;
  }
  assert( sqlite3PagerIswriteable(pChild->pDbPage) );
  assert( sqlite3PagerIswriteable(pRoot->pDbPage) );
  assert( pChild->nCell==pRoot->nCell );
................................................................................
  int szNew;
  int idx;
  MemPage *pPage;
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;
  unsigned char *oldCell;
  unsigned char *newCell = 0;






  assert( cursorHoldsMutex(pCur) );
  assert( pCur->wrFlag && pBt->inTransaction==TRANS_WRITE && !pBt->readOnly );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );

  /* Assert that the caller has been consistent. If this cursor was opened
  ** expecting an index b-tree, then the caller should be inserting blob
................................................................................
  /* If this is an insert into a table b-tree, invalidate any incrblob 
  ** cursors open on the row being replaced (assuming this is a replace
  ** operation - if it is not, the following is a no-op).  */
  if( pCur->pKeyInfo==0 ){
    invalidateIncrblobCursors(p, pCur->pgnoRoot, nKey, 0);
  }

  if( pCur->eState==CURSOR_FAULT ){
    assert( pCur->skipNext!=SQLITE_OK );
    return pCur->skipNext;
  }

  /* Save the positions of any other cursors open on this table.
  **
  ** In some cases, the call to btreeMoveto() below is a no-op. For
  ** example, when inserting data into a table with auto-generated integer
  ** keys, the VDBE layer invokes sqlite3BtreeLast() to figure out the 
  ** integer key to use. It then calls this function to actually insert the 
  ** data into the intkey B-Tree. In this case btreeMoveto() recognizes
................................................................................
    }
    oldCell = findCell(pPage, idx);
    if( !pPage->leaf ){
      memcpy(newCell, oldCell, 4);
    }
    szOld = cellSizePtr(pPage, oldCell);
    rc = clearCell(pPage, oldCell);
    if( rc ) goto end_insert;
    rc = dropCell(pPage, idx, szOld);
    if( rc!=SQLITE_OK ) {
      goto end_insert;
    }
  }else if( loc<0 && pPage->nCell>0 ){
    assert( pPage->leaf );
    idx = ++pCur->aiIdx[pCur->iPage];
  }else{
    assert( pPage->leaf );
  }
  rc = insertCell(pPage, idx, newCell, szNew, 0, 0);
  assert( rc!=SQLITE_OK || pPage->nCell>0 || pPage->nOverflow>0 );

  /* If no error has occured and pPage has an overflow cell, call balance() 
  ** to redistribute the cells within the tree. Since balance() may move
  ** the cursor, zero the BtCursor.info.nSize and BtCursor.validNKey
  ** variables.
  **
................................................................................
  ** entry and finally remove the cell itself from within the page.  
  */
  rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
  if( rc ) return rc;
  rc = sqlite3PagerWrite(pPage->pDbPage);
  if( rc ) return rc;
  rc = clearCell(pPage, pCell);
  if( rc ) return rc;
  rc = dropCell(pPage, iCellIdx, cellSizePtr(pPage, pCell));
  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.  */
................................................................................
    nCell = cellSizePtr(pLeaf, pCell);
    assert( MX_CELL_SIZE(pBt)>=nCell );

    allocateTempSpace(pBt);
    pTmp = pBt->pTmpSpace;

    rc = sqlite3PagerWrite(pLeaf->pDbPage);
    if( rc ) return rc;
    rc = insertCell(pPage, iCellIdx, pCell-4, nCell+4, pTmp, n);
    if( rc ) return rc;
    rc = dropCell(pLeaf, pLeaf->nCell-1, nCell);
    if( rc ) return rc;
  }

  /* Balance the tree. If the entry deleted was located on a leaf page,
  ** then the cursor still points to that page. In this case the first
  ** call to balance() repairs the tree, and the if(...) condition is
  ** never true.
................................................................................
        return rc;
      }
    }else{
      pRoot = pPageMove;
    } 

    /* Update the pointer-map and meta-data with the new root-page number. */
    rc = ptrmapPut(pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0);
    if( rc ){
      releasePage(pRoot);
      return rc;
    }
    rc = sqlite3BtreeUpdateMeta(p, 4, pgnoRoot);
    if( rc ){
      releasePage(pRoot);







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1017
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2539
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5119
....
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....
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....
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5280
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....
5299
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5309


5310
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....
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....
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....
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....
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....
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....
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....
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....
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....
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6454
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....
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** 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 1.692 2009/07/20 17:11:50 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
}

/*
** Write an entry into the pointer map.
**
** This routine updates the pointer map entry for page number 'key'
** so that it maps to type 'eType' and parent page number 'pgno'.
**
** If *pRC is initially non-zero (non-SQLITE_OK) then this routine is
** a no-op.  If an error occurs, the appropriate error code is written
** into *pRC.
*/
static void ptrmapPut(BtShared *pBt, Pgno key, u8 eType, Pgno parent, int *pRC){
  DbPage *pDbPage;  /* The pointer map page */
  u8 *pPtrmap;      /* The pointer map data */
  Pgno iPtrmap;     /* The pointer map page number */
  int offset;       /* Offset in pointer map page */
  int rc;           /* Return code from subfunctions */

  if( *pRC ) return;

  assert( sqlite3_mutex_held(pBt->mutex) );
  /* The master-journal page number must never be used as a pointer map page */
  assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );

  assert( pBt->autoVacuum );
  if( key==0 ){
    *pRC = SQLITE_CORRUPT_BKPT;
    return;
  }
  iPtrmap = PTRMAP_PAGENO(pBt, key);
  rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
  if( rc!=SQLITE_OK ){
    *pRC = rc;
    return;
  }
  offset = PTRMAP_PTROFFSET(iPtrmap, key);
  if( offset<0 ){
    *pRC = SQLITE_CORRUPT_BKPT;
    goto ptrmap_exit;
  }
  pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);

  if( eType!=pPtrmap[offset] || get4byte(&pPtrmap[offset+1])!=parent ){
    TRACE(("PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent));
    *pRC= rc = sqlite3PagerWrite(pDbPage);
    if( rc==SQLITE_OK ){
      pPtrmap[offset] = eType;
      put4byte(&pPtrmap[offset+1], parent);
    }
  }

ptrmap_exit:
  sqlite3PagerUnref(pDbPage);

}

/*
** Read an entry from the pointer map.
**
** This routine retrieves the pointer map entry for page 'key', writing
** the type and parent page number to *pEType and *pPgno respectively.
................................................................................

  sqlite3PagerUnref(pDbPage);
  if( *pEType<1 || *pEType>5 ) return SQLITE_CORRUPT_BKPT;
  return SQLITE_OK;
}

#else /* if defined SQLITE_OMIT_AUTOVACUUM */
  #define ptrmapPut(w,x,y,z,rc)
  #define ptrmapGet(w,x,y,z) SQLITE_OK
  #define ptrmapPutOvflPtr(x, y, rc)
#endif

/*
** Given a btree page and a cell index (0 means the first cell on
** the page, 1 means the second cell, and so forth) return a pointer
** to the cell content.
**
................................................................................

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** If the cell pCell, part of page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
static void ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell, int *pRC){
  CellInfo info;
  if( *pRC ) return;
  assert( pCell!=0 );
  btreeParseCellPtr(pPage, pCell, &info);
  assert( (info.nData+(pPage->intKey?0:info.nKey))==info.nPayload );
  if( info.iOverflow ){
    Pgno ovfl = get4byte(&pCell[info.iOverflow]);
    ptrmapPut(pPage->pBt, ovfl, PTRMAP_OVERFLOW1, pPage->pgno, pRC);
  }

}
#endif


/*
** Defragment the page given.  All Cells are moved to the
** end of the page and all free space is collected into one
................................................................................
    goto set_child_ptrmaps_out;
  }
  nCell = pPage->nCell;

  for(i=0; i<nCell; i++){
    u8 *pCell = findCell(pPage, i);

    ptrmapPutOvflPtr(pPage, pCell, &rc);




    if( !pPage->leaf ){
      Pgno childPgno = get4byte(pCell);
      ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno, &rc);

    }
  }

  if( !pPage->leaf ){
    Pgno childPgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno, &rc);
  }

set_child_ptrmaps_out:
  pPage->isInit = isInitOrig;
  return rc;
}

................................................................................
    rc = setChildPtrmaps(pDbPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }else{
    Pgno nextOvfl = get4byte(pDbPage->aData);
    if( nextOvfl!=0 ){
      ptrmapPut(pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage, &rc);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
................................................................................
    if( rc!=SQLITE_OK ){
      releasePage(pPtrPage);
      return rc;
    }
    rc = modifyPagePointer(pPtrPage, iDbPage, iFreePage, eType);
    releasePage(pPtrPage);
    if( rc==SQLITE_OK ){
      ptrmapPut(pBt, iFreePage, eType, iPtrPage, &rc);
    }
  }
  return rc;
}

/* Forward declaration required by incrVacuumStep(). */
static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);
................................................................................
  memset(pPage->aData, 0, pPage->pBt->pageSize);
#endif

  /* If the database supports auto-vacuum, write an entry in the pointer-map
  ** to indicate that the page is free.
  */
  if( ISAUTOVACUUM ){
    ptrmapPut(pBt, iPage, PTRMAP_FREEPAGE, 0, &rc);
    if( rc ) goto freepage_out;
  }

  /* Now manipulate the actual database free-list structure. There are two
  ** possibilities. If the free-list is currently empty, or if the first
  ** trunk page in the free-list is full, then this page will become a
  ** new free-list trunk page. Otherwise, it will become a leaf of the
................................................................................
      ** to the pointer-map. If we write nothing to this pointer-map slot,
      ** then the optimistic overflow chain processing in clearCell()
      ** may misinterpret the uninitialised values and delete the
      ** wrong pages from the database.
      */
      if( pBt->autoVacuum && rc==SQLITE_OK ){
        u8 eType = (pgnoPtrmap?PTRMAP_OVERFLOW2:PTRMAP_OVERFLOW1);
        ptrmapPut(pBt, pgnoOvfl, eType, pgnoPtrmap, &rc);
        if( rc ){
          releasePage(pOvfl);
        }
      }
#endif
      if( rc ){
        releasePage(pToRelease);
................................................................................
** Remove the i-th cell from pPage.  This routine effects pPage only.
** The cell content is not freed or deallocated.  It is assumed that
** the cell content has been copied someplace else.  This routine just
** removes the reference to the cell from pPage.
**
** "sz" must be the number of bytes in the cell.
*/
static void dropCell(MemPage *pPage, int idx, int sz, int *pRC){
  int i;          /* Loop counter */
  int pc;         /* Offset to cell content of cell being deleted */
  u8 *data;       /* pPage->aData */
  u8 *ptr;        /* Used to move bytes around within data[] */
  int rc;         /* The return code */

  if( *pRC ) return;

  assert( idx>=0 && idx<pPage->nCell );
  assert( sz==cellSize(pPage, idx) );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  data = pPage->aData;
  ptr = &data[pPage->cellOffset + 2*idx];
  pc = get2byte(ptr);
  if( (pc<pPage->hdrOffset+6+pPage->childPtrSize)
     || (pc+sz>pPage->pBt->usableSize) ){
    *pRC = SQLITE_CORRUPT_BKPT;
    return;
  }
  rc = freeSpace(pPage, pc, sz);
  if( rc ){
    *pRC = rc;
    return;
  }
  for(i=idx+1; i<pPage->nCell; i++, ptr+=2){
    ptr[0] = ptr[2];
    ptr[1] = ptr[3];
  }
  pPage->nCell--;
  put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
  pPage->nFree += 2;

}

/*
** 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
................................................................................
** pPage->nOverflow is incremented.
**
** If nSkip is non-zero, then do not copy the first nSkip bytes of the
** cell. The caller will overwrite them after this function returns. If
** nSkip is non-zero, then pCell may not point to an invalid memory location 
** (but pCell+nSkip is always valid).
*/
static void insertCell(
  MemPage *pPage,   /* Page into which we are copying */
  int i,            /* New cell becomes the i-th cell of the page */
  u8 *pCell,        /* Content of the new cell */
  int sz,           /* Bytes of content in pCell */
  u8 *pTemp,        /* Temp storage space for pCell, if needed */
  Pgno iChild,      /* If non-zero, replace first 4 bytes with this value */
  int *pRC          /* Read and write return code from here */
){
  int idx;          /* Where to write new cell content in data[] */
  int j;            /* Loop counter */
  int end;          /* First byte past the last cell pointer in data[] */
  int ins;          /* Index in data[] where new cell pointer is inserted */
  int cellOffset;   /* Address of first cell pointer in data[] */
  u8 *data;         /* The content of the whole page */
  u8 *ptr;          /* Used for moving information around in data[] */

  int nSkip = (iChild ? 4 : 0);

  if( *pRC ) return;

  assert( i>=0 && i<=pPage->nCell+pPage->nOverflow );
  assert( pPage->nCell<=MX_CELL(pPage->pBt) && MX_CELL(pPage->pBt)<=5460 );
  assert( pPage->nOverflow<=ArraySize(pPage->aOvfl) );
  assert( sz==cellSizePtr(pPage, pCell) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  if( pPage->nOverflow || sz+2>pPage->nFree ){
................................................................................
    j = pPage->nOverflow++;
    assert( j<(int)(sizeof(pPage->aOvfl)/sizeof(pPage->aOvfl[0])) );
    pPage->aOvfl[j].pCell = pCell;
    pPage->aOvfl[j].idx = (u16)i;
  }else{
    int rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc!=SQLITE_OK ){
      *pRC = rc;
      return;
    }
    assert( sqlite3PagerIswriteable(pPage->pDbPage) );
    data = pPage->aData;
    cellOffset = pPage->cellOffset;
    end = cellOffset + 2*pPage->nCell;
    ins = cellOffset + 2*i;
    rc = allocateSpace(pPage, sz, &idx);
    if( rc ){ *pRC = rc; return; }
    assert( idx>=end+2 );
    if( idx+sz > pPage->pBt->usableSize ){
      *pRC = SQLITE_CORRUPT_BKPT;
      return;
    }
    pPage->nCell++;
    pPage->nFree -= (u16)(2 + sz);
    memcpy(&data[idx+nSkip], pCell+nSkip, sz-nSkip);
    if( iChild ){
      put4byte(&data[idx], iChild);
    }
................................................................................
    put2byte(&data[ins], idx);
    put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pPage->pBt->autoVacuum ){
      /* The cell may contain a pointer to an overflow page. If so, write
      ** the entry for the overflow page into the pointer map.
      */
      ptrmapPutOvflPtr(pPage, pCell, pRC);
    }
#endif
  }


}

/*
** Add a list of cells to a page.  The page should be initially empty.
** The cells are guaranteed to fit on the page.
*/
static void assemblePage(
................................................................................
    ** operations fails, the return code is set, but the contents
    ** of the parent page are still manipulated by thh code below.
    ** That is Ok, at this point the parent page is guaranteed to
    ** be marked as dirty. Returning an error code will cause a
    ** rollback, undoing any changes made to the parent page.
    */
    if( ISAUTOVACUUM ){
      ptrmapPut(pBt, pgnoNew, PTRMAP_BTREE, pParent->pgno, &rc);
      if( szCell>pNew->minLocal ){
        ptrmapPutOvflPtr(pNew, pCell, &rc);
      }
    }
  
    /* Create a divider cell to insert into pParent. The divider cell
    ** consists of a 4-byte page number (the page number of pPage) and
    ** a variable length key value (which must be the same value as the
    ** largest key on pPage).
................................................................................
    pCell = findCell(pPage, pPage->nCell-1);
    pStop = &pCell[9];
    while( (*(pCell++)&0x80) && pCell<pStop );
    pStop = &pCell[9];
    while( ((*(pOut++) = *(pCell++))&0x80) && pCell<pStop );

    /* Insert the new divider cell into pParent. */
    insertCell(pParent, pParent->nCell, pSpace, (int)(pOut-pSpace),
               0, pPage->pgno, &rc);

    /* Set the right-child pointer of pParent to point to the new page. */
    put4byte(&pParent->aData[pParent->hdrOffset+8], pgnoNew);
  
    /* Release the reference to the new page. */
    releasePage(pNew);
  }
................................................................................
      ** In this case, temporarily copy the cell into the aOvflSpace[]
      ** buffer. It will be copied out again as soon as the aSpace[] buffer
      ** is allocated.  */
#ifdef SQLITE_SECURE_DELETE
      memcpy(&aOvflSpace[apDiv[i]-pParent->aData], apDiv[i], szNew[i]);
      apDiv[i] = &aOvflSpace[apDiv[i]-pParent->aData];
#endif
      dropCell(pParent, i+nxDiv-pParent->nOverflow, szNew[i], &rc);
    }
  }

  /* Make nMaxCells a multiple of 4 in order to preserve 8-byte
  ** alignment */
  nMaxCells = (nMaxCells + 3)&~3;

................................................................................
      rc = allocateBtreePage(pBt, &pNew, &pgno, pgno, 0);
      if( rc ) goto balance_cleanup;
      apNew[i] = pNew;
      nNew++;

      /* Set the pointer-map entry for the new sibling page. */
      if( ISAUTOVACUUM ){
        ptrmapPut(pBt, pNew->pgno, PTRMAP_BTREE, pParent->pgno, &rc);
        if( rc!=SQLITE_OK ){
          goto balance_cleanup;
        }
      }
    }
  }

................................................................................
          assert(leafCorrection==4);
          sz = cellSizePtr(pParent, pCell);
        }
      }
      iOvflSpace += sz;
      assert( sz<=pBt->pageSize/4 );
      assert( iOvflSpace<=pBt->pageSize );
      insertCell(pParent, nxDiv, pCell, sz, pTemp, pNew->pgno, &rc);
      if( rc!=SQLITE_OK ) goto balance_cleanup;
      assert( sqlite3PagerIswriteable(pParent->pDbPage) );

      j++;
      nxDiv++;
    }
  }
................................................................................

      /* If the cell was originally divider cell (and is not now) or
      ** an overflow cell, or if the cell was located on a different sibling
      ** page before the balancing, then the pointer map entries associated
      ** with any child or overflow pages need to be updated.  */
      if( isDivider || pOld->pgno!=pNew->pgno ){
        if( !leafCorrection ){
          ptrmapPut(pBt, get4byte(apCell[i]), PTRMAP_BTREE, pNew->pgno, &rc);
        }
        if( szCell[i]>pNew->minLocal ){
          ptrmapPutOvflPtr(pNew, apCell[i], &rc);
        }
      }
    }

    if( !leafCorrection ){
      for(i=0; i<nNew; i++){
        u32 key = get4byte(&apNew[i]->aData[8]);
        ptrmapPut(pBt, key, PTRMAP_BTREE, apNew[i]->pgno, &rc);
      }
    }

#if 0
    /* The ptrmapCheckPages() contains assert() statements that verify that
    ** all pointer map pages are set correctly. This is helpful while 
    ** debugging. This is usually disabled because a corrupt database may
................................................................................
  assert( pRoot->nOverflow>0 );
  assert( sqlite3_mutex_held(pBt->mutex) );

  /* Make pRoot, the root page of the b-tree, writable. Allocate a new 
  ** page that will become the new right-child of pPage. Copy the contents
  ** of the node stored on pRoot into the new child page.
  */
  rc = sqlite3PagerWrite(pRoot->pDbPage);
  if( rc==SQLITE_OK ){
    rc = allocateBtreePage(pBt,&pChild,&pgnoChild,pRoot->pgno,0);
    if( rc==SQLITE_OK ){
      rc = copyNodeContent(pRoot, pChild);
      if( ISAUTOVACUUM ){
        ptrmapPut(pBt, pgnoChild, PTRMAP_BTREE, pRoot->pgno, &rc);
      }
    }
  }
  if( rc ){
    *ppChild = 0;
    releasePage(pChild);
    return rc;
  }
  assert( sqlite3PagerIswriteable(pChild->pDbPage) );
  assert( sqlite3PagerIswriteable(pRoot->pDbPage) );
  assert( pChild->nCell==pRoot->nCell );
................................................................................
  int szNew;
  int idx;
  MemPage *pPage;
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;
  unsigned char *oldCell;
  unsigned char *newCell = 0;

  if( pCur->eState==CURSOR_FAULT ){
    assert( pCur->skipNext!=SQLITE_OK );
    return pCur->skipNext;
  }

  assert( cursorHoldsMutex(pCur) );
  assert( pCur->wrFlag && pBt->inTransaction==TRANS_WRITE && !pBt->readOnly );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );

  /* Assert that the caller has been consistent. If this cursor was opened
  ** expecting an index b-tree, then the caller should be inserting blob
................................................................................
  /* If this is an insert into a table b-tree, invalidate any incrblob 
  ** cursors open on the row being replaced (assuming this is a replace
  ** operation - if it is not, the following is a no-op).  */
  if( pCur->pKeyInfo==0 ){
    invalidateIncrblobCursors(p, pCur->pgnoRoot, nKey, 0);
  }






  /* Save the positions of any other cursors open on this table.
  **
  ** In some cases, the call to btreeMoveto() below is a no-op. For
  ** example, when inserting data into a table with auto-generated integer
  ** keys, the VDBE layer invokes sqlite3BtreeLast() to figure out the 
  ** integer key to use. It then calls this function to actually insert the 
  ** data into the intkey B-Tree. In this case btreeMoveto() recognizes
................................................................................
    }
    oldCell = findCell(pPage, idx);
    if( !pPage->leaf ){
      memcpy(newCell, oldCell, 4);
    }
    szOld = cellSizePtr(pPage, oldCell);
    rc = clearCell(pPage, oldCell);

    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 );
  }
  insertCell(pPage, idx, newCell, szNew, 0, 0, &rc);
  assert( rc!=SQLITE_OK || pPage->nCell>0 || pPage->nOverflow>0 );

  /* If no error has occured and pPage has an overflow cell, call balance() 
  ** to redistribute the cells within the tree. Since balance() may move
  ** the cursor, zero the BtCursor.info.nSize and BtCursor.validNKey
  ** variables.
  **
................................................................................
  ** entry and finally remove the cell itself from within the page.  
  */
  rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
  if( rc ) return rc;
  rc = sqlite3PagerWrite(pPage->pDbPage);
  if( rc ) return rc;
  rc = clearCell(pPage, pCell);

  dropCell(pPage, iCellIdx, cellSizePtr(pPage, pCell), &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.  */
................................................................................
    nCell = cellSizePtr(pLeaf, pCell);
    assert( MX_CELL_SIZE(pBt)>=nCell );

    allocateTempSpace(pBt);
    pTmp = pBt->pTmpSpace;

    rc = sqlite3PagerWrite(pLeaf->pDbPage);

    insertCell(pPage, iCellIdx, pCell-4, nCell+4, pTmp, n, &rc);

    dropCell(pLeaf, pLeaf->nCell-1, nCell, &rc);
    if( rc ) return rc;
  }

  /* Balance the tree. If the entry deleted was located on a leaf page,
  ** then the cursor still points to that page. In this case the first
  ** call to balance() repairs the tree, and the if(...) condition is
  ** never true.
................................................................................
        return rc;
      }
    }else{
      pRoot = pPageMove;
    } 

    /* Update the pointer-map and meta-data with the new root-page number. */
    ptrmapPut(pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0, &rc);
    if( rc ){
      releasePage(pRoot);
      return rc;
    }
    rc = sqlite3BtreeUpdateMeta(p, 4, pgnoRoot);
    if( rc ){
      releasePage(pRoot);