SQLite

/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.240 2005/01/17 02:12:19 danielk1977 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.

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

  assert( pBt->autoVacuum );
  if( key==0 ){
    return SQLITE_CORRUPT;
  }
  iPtrmap = PTRMAP_PAGENO(pBt->usableSize, key);
  rc = sqlite3pager_get(pBt->pPager, iPtrmap, (void **)&pPtrmap);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  offset = PTRMAP_PTROFFSET(pBt->usableSize, key);

  }

  offset = PTRMAP_PTROFFSET(pBt->usableSize, key);
  if( pEType ) *pEType = pPtrmap[offset];
  if( pPgno ) *pPgno = get4byte(&pPtrmap[offset+1]);

  sqlite3pager_unref(pPtrmap);
  if( *pEType<1 || *pEType>5 ) return SQLITE_CORRUPT;
  return SQLITE_OK;
}

#endif /* SQLITE_OMIT_AUTOVACUUM */

/*
** Given a btree page and a cell index (0 means the first cell on

  int isInitOrig = pPage->isInit;
  Pgno pgno = pPage->pgno;

  initPage(pPage, 0);
  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;
    }

**
** PTRMAP_OVERFLOW1: pPage is a btree-page. The pointer points at an overflow
**                   page pointed to by one of the cells on pPage.
**
** PTRMAP_OVERFLOW2: pPage is an overflow-page. The pointer points at the next
**                   overflow page in the list.
*/
static int modifyPagePointer(MemPage *pPage, Pgno iFrom, Pgno iTo, u8 eType){

  if( eType==PTRMAP_OVERFLOW2 ){
    /* The pointer is always the first 4 bytes of the page in this case.  */
    if( get4byte(pPage->aData)!=iFrom ){
      return SQLITE_CORRUPT;
    }
    put4byte(pPage->aData, iTo);
  }else{
    int isInitOrig = pPage->isInit;
    int i;
    int nCell;

    initPage(pPage, 0);

          put4byte(pCell, iTo);
          break;
        }
      }
    }
  
    if( i==nCell ){
      if( eType!=PTRMAP_BTREE || 
          get4byte(&pPage->aData[pPage->hdrOffset+8])!=iFrom ){
        return SQLITE_CORRUPT;
      }
      put4byte(&pPage->aData[pPage->hdrOffset+8], iTo);
    }

    pPage->isInit = isInitOrig;
  }
  return SQLITE_OK;
}


/*
** Move the open database page pDbPage to location iFreePage in the 
** database. The pDbPage reference remains valid.
*/

    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;
      }
    }
  }

      return rc;
    }
    rc = sqlite3pager_write(pPtrPage->aData);
    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 autoVacuumCommit(). */
static int allocatePage(Btree *, MemPage **, Pgno *, Pgno, u8);

  MemPage *pFreeMemPage = 0; /* "" */

#ifndef NDEBUG
  int nRef = *sqlite3pager_stats(pPager);
#endif

  assert( pBt->autoVacuum );
  if( PTRMAP_ISPAGE(pgsz, sqlite3pager_pagecount(pPager)) ){
    return SQLITE_CORRUPT;
  }

  /* Figure out how many free-pages are in the database. If there are no
  ** free pages, then auto-vacuum is a no-op.
  */
  nFreeList = get4byte(&pBt->pPage1->aData[36]);
  if( nFreeList==0 ){
    *nTrunc = 0;