** 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 1.335 2007/02/10 19:22:36 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.
................................................................................
  pPage->isInit = 1;
}

/*
** Get a page from the pager.  Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
*/
static int getPage(BtShared *pBt, Pgno pgno, MemPage **ppPage){
  int rc;
  unsigned char *aData;
  MemPage *pPage;
  rc = sqlite3pager_get(pBt->pPager, pgno, (void**)&aData);
  if( rc ) return rc;
  pPage = (MemPage*)&aData[pBt->pageSize];
  pPage->aData = aData;
  pPage->pBt = pBt;
  pPage->pgno = pgno;
  pPage->hdrOffset = pPage->pgno==1 ? 100 : 0;
  *ppPage = pPage;
................................................................................
  MemPage **ppPage,    /* Write the page pointer here */
  MemPage *pParent     /* Parent of the page */
){
  int rc;
  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT; 
  }
  rc = getPage(pBt, pgno, ppPage);
  if( rc==SQLITE_OK && (*ppPage)->isInit==0 ){
    rc = initPage(*ppPage, pParent);
  }
  return rc;
}

/*
................................................................................
** is returned if we run out of memory.  SQLITE_PROTOCOL is returned
** if there is a locking protocol violation.
*/
static int lockBtree(BtShared *pBt){
  int rc, pageSize;
  MemPage *pPage1;
  if( pBt->pPage1 ) return SQLITE_OK;
  rc = getPage(pBt, 1, &pPage1);
  if( rc!=SQLITE_OK ) return rc;
  

  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */
  rc = SQLITE_NOTADB;
................................................................................
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
  ** that it points at iFreePage. Also fix the pointer map entry for
  ** iPtrPage.
  */
  if( eType!=PTRMAP_ROOTPAGE ){
    rc = getPage(pBt, iPtrPage, &pPtrPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    rc = sqlite3pager_write(pPtrPage->aData);
    if( rc!=SQLITE_OK ){
      releasePage(pPtrPage);
      return rc;
................................................................................
      goto autovacuum_out;
    }

    /* If iDbPage is free, do not swap it.  */
    if( eType==PTRMAP_FREEPAGE ){
      continue;
    }
    rc = getPage(pBt, iDbPage, &pDbMemPage);
    if( rc!=SQLITE_OK ) goto autovacuum_out;

    /* Find the next page in the free-list that is not already at the end 
    ** of the file. A page can be pulled off the free list using the 
    ** allocatePage() routine.
    */
    do{
................................................................................
    if( rc2!=SQLITE_OK ){
      rc = rc2;
    }

    /* The rollback may have destroyed the pPage1->aData value.  So
    ** call getPage() on page 1 again to make sure pPage1->aData is
    ** set correctly. */
    if( getPage(pBt, 1, &pPage1)==SQLITE_OK ){
      releasePage(pPage1);
    }
    assert( countWriteCursors(pBt)==0 );
    pBt->inTransaction = TRANS_READ;
  }

  if( p->inTrans!=TRANS_NONE ){
................................................................................
    do {
      pPrevTrunk = pTrunk;
      if( pPrevTrunk ){
        iTrunk = get4byte(&pPrevTrunk->aData[0]);
      }else{
        iTrunk = get4byte(&pPage1->aData[32]);
      }
      rc = getPage(pBt, iTrunk, &pTrunk);
      if( rc ){
        pTrunk = 0;
        goto end_allocate_page;
      }

      k = get4byte(&pTrunk->aData[4]);
      if( k==0 && !searchList ){
................................................................................
        }else{
          /* The trunk page is required by the caller but it contains 
          ** pointers to free-list leaves. The first leaf becomes a trunk
          ** page in this case.
          */
          MemPage *pNewTrunk;
          Pgno iNewTrunk = get4byte(&pTrunk->aData[8]);
          rc = getPage(pBt, iNewTrunk, &pNewTrunk);
          if( rc!=SQLITE_OK ){
            goto end_allocate_page;
          }
          rc = sqlite3pager_write(pNewTrunk->aData);
          if( rc!=SQLITE_OK ){
            releasePage(pNewTrunk);
            goto end_allocate_page;
................................................................................
          TRACE(("ALLOCATE: %d was leaf %d of %d on trunk %d"
                 ": %d more free pages\n",
                 *pPgno, closest+1, k, pTrunk->pgno, n-1));
          if( closest<k-1 ){
            memcpy(&aData[8+closest*4], &aData[4+k*4], 4);
          }
          put4byte(&aData[4], k-1);
          rc = getPage(pBt, *pPgno, ppPage);
          if( rc==SQLITE_OK ){
            sqlite3pager_dont_rollback((*ppPage)->aData);
            rc = sqlite3pager_write((*ppPage)->aData);
            if( rc!=SQLITE_OK ){
              releasePage(*ppPage);
            }
          }
................................................................................
      TRACE(("ALLOCATE: %d from end of file (pointer-map page)\n", *pPgno));
      assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
      (*pPgno)++;
    }
#endif

    assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
    rc = getPage(pBt, *pPgno, ppPage);
    if( rc ) return rc;
    rc = sqlite3pager_write((*ppPage)->aData);
    if( rc!=SQLITE_OK ){
      releasePage(*ppPage);
    }
    TRACE(("ALLOCATE: %d from end of file\n", *pPgno));
  }
................................................................................
    memset(pPage->aData, 0, 8);
    put4byte(&pPage1->aData[32], pPage->pgno);
    TRACE(("FREE-PAGE: %d first\n", pPage->pgno));
  }else{
    /* Other free pages already exist.  Retrive the first trunk page
    ** of the freelist and find out how many leaves it has. */
    MemPage *pTrunk;
    rc = getPage(pBt, get4byte(&pPage1->aData[32]), &pTrunk);
    if( rc ) return rc;
    k = get4byte(&pTrunk->aData[4]);
    if( k>=pBt->usableSize/4 - 8 ){
      /* The trunk is full.  Turn the page being freed into a new
      ** trunk page with no leaves. */
      rc = sqlite3pager_write(pPage->aData);
      if( rc ) return rc;
................................................................................
  }
  ovflPgno = get4byte(&pCell[info.iOverflow]);
  while( ovflPgno!=0 ){
    MemPage *pOvfl;
    if( ovflPgno>sqlite3pager_pagecount(pBt->pPager) ){
      return SQLITE_CORRUPT_BKPT;
    }
    rc = getPage(pBt, ovflPgno, &pOvfl);
    if( rc ) return rc;
    ovflPgno = get4byte(pOvfl->aData);
    rc = freePage(pOvfl);
    sqlite3pager_unref(pOvfl->aData);
    if( rc ) return rc;
  }
  return SQLITE_OK;
................................................................................
      */
      if( pBt->autoVacuum && pgnoPtrmap!=0 && rc==SQLITE_OK ){
        rc = ptrmapPut(pBt, pgnoOvfl, PTRMAP_OVERFLOW2, pgnoPtrmap);
      }
#endif
      if( rc ){
        releasePage(pToRelease);
        /* clearCell(pPage, pCell); */
        return rc;
      }
      put4byte(pPrior, pgnoOvfl);
      releasePage(pToRelease);
      pToRelease = pOvfl;
      pPrior = pOvfl->aData;
      put4byte(pPrior, 0);
................................................................................
    ** case, then do not do the transfer.  Leave page 1 empty except
    ** for the right-pointer to the child page.  The child page becomes
    ** the virtual root of the tree.
    */
    pgnoChild = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    assert( pgnoChild>0 );
    assert( pgnoChild<=sqlite3pager_pagecount(pPage->pBt->pPager) );
    rc = getPage(pPage->pBt, pgnoChild, &pChild);
    if( rc ) goto end_shallow_balance;
    if( pPage->pgno==1 ){
      rc = initPage(pChild, pPage);
      if( rc ) goto end_shallow_balance;
      assert( pChild->nOverflow==0 );
      if( pChild->nFree>=100 ){
        /* The child information will fit on the root page, so do the
................................................................................
    }

    if( pgnoMove!=pgnoRoot ){
      u8 eType;
      Pgno iPtrPage;

      releasePage(pPageMove);
      rc = getPage(pBt, pgnoRoot, &pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = ptrmapGet(pBt, pgnoRoot, &eType, &iPtrPage);
      if( rc!=SQLITE_OK || eType==PTRMAP_ROOTPAGE || eType==PTRMAP_FREEPAGE ){
        releasePage(pRoot);
        return rc;
................................................................................
        return rc;
      }
      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove);
      releasePage(pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = getPage(pBt, pgnoRoot, &pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = sqlite3pager_write(pRoot->aData);
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
................................................................................

  if( pgno>sqlite3pager_pagecount(pBt->pPager) ){
    return SQLITE_CORRUPT_BKPT;
  }

  rc = getAndInitPage(pBt, pgno, &pPage, pParent);
  if( rc ) goto cleardatabasepage_out;
  rc = sqlite3pager_write(pPage->aData);
  if( rc ) goto cleardatabasepage_out;
  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
    if( !pPage->leaf ){
      rc = clearDatabasePage(pBt, get4byte(pCell), pPage->pParent, 1);
      if( rc ) goto cleardatabasepage_out;
    }
    rc = clearCell(pPage, pCell);
................................................................................
  }
  if( !pPage->leaf ){
    rc = clearDatabasePage(pBt, get4byte(&pPage->aData[8]), pPage->pParent, 1);
    if( rc ) goto cleardatabasepage_out;
  }
  if( freePageFlag ){
    rc = freePage(pPage);
  }else{
    zeroPage(pPage, pPage->aData[0] | PTF_LEAF);
  }

cleardatabasepage_out:
  releasePage(pPage);
  return rc;
}
................................................................................
  ** root page. If an open cursor was using this page a problem would 
  ** occur.
  */
  if( pBt->pCursor ){
    return SQLITE_LOCKED;
  }

  rc = getPage(pBt, (Pgno)iTable, &pPage);
  if( rc ) return rc;
  rc = sqlite3BtreeClearTable(p, iTable);
  if( rc ){
    releasePage(pPage);
    return rc;
  }

................................................................................
      }else{
        /* The table being dropped does not have the largest root-page
        ** number in the database. So move the page that does into the 
        ** gap left by the deleted root-page.
        */
        MemPage *pMove;
        releasePage(pPage);
        rc = getPage(pBt, maxRootPgno, &pMove);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = relocatePage(pBt, pMove, PTRMAP_ROOTPAGE, 0, iTable);
        releasePage(pMove);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = getPage(pBt, maxRootPgno, &pMove);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = freePage(pMove);
        releasePage(pMove);
        if( rc!=SQLITE_OK ){
          return rc;
................................................................................
  int hdr;
  int nCell;
  int isInit;
  unsigned char *data;
  char range[20];
  unsigned char payload[20];

  rc = getPage(pBt, (Pgno)pgno, &pPage);
  isInit = pPage->isInit;
  if( pPage->isInit==0 ){
    initPage(pPage, pParent);
  }
  if( rc ){
    return rc;
  }
................................................................................

  /* Check that the page exists
  */
  pBt = pCheck->pBt;
  usableSize = pBt->usableSize;
  if( iPage==0 ) return 0;
  if( checkRef(pCheck, iPage, zParentContext) ) return 0;
  if( (rc = getPage(pBt, (Pgno)iPage, &pPage))!=0 ){
    checkAppendMsg(pCheck, zContext,
       "unable to get the page. error code=%d", rc);
    return 0;
  }
  if( (rc = initPage(pPage, pParent))!=0 ){
    checkAppendMsg(pCheck, zContext, "initPage() returns error code %d", rc);
    releasePage(pPage);

** 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 1.336 2007/03/04 13:15:28 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.
................................................................................
  pPage->isInit = 1;
}

/*
** Get a page from the pager.  Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
*/
static int getPage(BtShared *pBt, Pgno pgno, MemPage **ppPage, int clrFlag){
  int rc;
  unsigned char *aData;
  MemPage *pPage;
  rc = sqlite3pager_acquire(pBt->pPager, pgno, (void**)&aData, clrFlag);
  if( rc ) return rc;
  pPage = (MemPage*)&aData[pBt->pageSize];
  pPage->aData = aData;
  pPage->pBt = pBt;
  pPage->pgno = pgno;
  pPage->hdrOffset = pPage->pgno==1 ? 100 : 0;
  *ppPage = pPage;
................................................................................
  MemPage **ppPage,    /* Write the page pointer here */
  MemPage *pParent     /* Parent of the page */
){
  int rc;
  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT; 
  }
  rc = getPage(pBt, pgno, ppPage, 0);
  if( rc==SQLITE_OK && (*ppPage)->isInit==0 ){
    rc = initPage(*ppPage, pParent);
  }
  return rc;
}

/*
................................................................................
** is returned if we run out of memory.  SQLITE_PROTOCOL is returned
** if there is a locking protocol violation.
*/
static int lockBtree(BtShared *pBt){
  int rc, pageSize;
  MemPage *pPage1;
  if( pBt->pPage1 ) return SQLITE_OK;
  rc = getPage(pBt, 1, &pPage1, 0);
  if( rc!=SQLITE_OK ) return rc;
  

  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */
  rc = SQLITE_NOTADB;
................................................................................
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
  ** that it points at iFreePage. Also fix the pointer map entry for
  ** iPtrPage.
  */
  if( eType!=PTRMAP_ROOTPAGE ){
    rc = getPage(pBt, iPtrPage, &pPtrPage, 0);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    rc = sqlite3pager_write(pPtrPage->aData);
    if( rc!=SQLITE_OK ){
      releasePage(pPtrPage);
      return rc;
................................................................................
      goto autovacuum_out;
    }

    /* If iDbPage is free, do not swap it.  */
    if( eType==PTRMAP_FREEPAGE ){
      continue;
    }
    rc = getPage(pBt, iDbPage, &pDbMemPage, 0);
    if( rc!=SQLITE_OK ) goto autovacuum_out;

    /* Find the next page in the free-list that is not already at the end 
    ** of the file. A page can be pulled off the free list using the 
    ** allocatePage() routine.
    */
    do{
................................................................................
    if( rc2!=SQLITE_OK ){
      rc = rc2;
    }

    /* The rollback may have destroyed the pPage1->aData value.  So
    ** call getPage() on page 1 again to make sure pPage1->aData is
    ** set correctly. */
    if( getPage(pBt, 1, &pPage1, 0)==SQLITE_OK ){
      releasePage(pPage1);
    }
    assert( countWriteCursors(pBt)==0 );
    pBt->inTransaction = TRANS_READ;
  }

  if( p->inTrans!=TRANS_NONE ){
................................................................................
    do {
      pPrevTrunk = pTrunk;
      if( pPrevTrunk ){
        iTrunk = get4byte(&pPrevTrunk->aData[0]);
      }else{
        iTrunk = get4byte(&pPage1->aData[32]);
      }
      rc = getPage(pBt, iTrunk, &pTrunk, 0);
      if( rc ){
        pTrunk = 0;
        goto end_allocate_page;
      }

      k = get4byte(&pTrunk->aData[4]);
      if( k==0 && !searchList ){
................................................................................
        }else{
          /* The trunk page is required by the caller but it contains 
          ** pointers to free-list leaves. The first leaf becomes a trunk
          ** page in this case.
          */
          MemPage *pNewTrunk;
          Pgno iNewTrunk = get4byte(&pTrunk->aData[8]);
          rc = getPage(pBt, iNewTrunk, &pNewTrunk, 0);
          if( rc!=SQLITE_OK ){
            goto end_allocate_page;
          }
          rc = sqlite3pager_write(pNewTrunk->aData);
          if( rc!=SQLITE_OK ){
            releasePage(pNewTrunk);
            goto end_allocate_page;
................................................................................
          TRACE(("ALLOCATE: %d was leaf %d of %d on trunk %d"
                 ": %d more free pages\n",
                 *pPgno, closest+1, k, pTrunk->pgno, n-1));
          if( closest<k-1 ){
            memcpy(&aData[8+closest*4], &aData[4+k*4], 4);
          }
          put4byte(&aData[4], k-1);
          rc = getPage(pBt, *pPgno, ppPage, 1);
          if( rc==SQLITE_OK ){
            sqlite3pager_dont_rollback((*ppPage)->aData);
            rc = sqlite3pager_write((*ppPage)->aData);
            if( rc!=SQLITE_OK ){
              releasePage(*ppPage);
            }
          }
................................................................................
      TRACE(("ALLOCATE: %d from end of file (pointer-map page)\n", *pPgno));
      assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
      (*pPgno)++;
    }
#endif

    assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
    rc = getPage(pBt, *pPgno, ppPage, 0);
    if( rc ) return rc;
    rc = sqlite3pager_write((*ppPage)->aData);
    if( rc!=SQLITE_OK ){
      releasePage(*ppPage);
    }
    TRACE(("ALLOCATE: %d from end of file\n", *pPgno));
  }
................................................................................
    memset(pPage->aData, 0, 8);
    put4byte(&pPage1->aData[32], pPage->pgno);
    TRACE(("FREE-PAGE: %d first\n", pPage->pgno));
  }else{
    /* Other free pages already exist.  Retrive the first trunk page
    ** of the freelist and find out how many leaves it has. */
    MemPage *pTrunk;
    rc = getPage(pBt, get4byte(&pPage1->aData[32]), &pTrunk, 0);
    if( rc ) return rc;
    k = get4byte(&pTrunk->aData[4]);
    if( k>=pBt->usableSize/4 - 8 ){
      /* The trunk is full.  Turn the page being freed into a new
      ** trunk page with no leaves. */
      rc = sqlite3pager_write(pPage->aData);
      if( rc ) return rc;
................................................................................
  }
  ovflPgno = get4byte(&pCell[info.iOverflow]);
  while( ovflPgno!=0 ){
    MemPage *pOvfl;
    if( ovflPgno>sqlite3pager_pagecount(pBt->pPager) ){
      return SQLITE_CORRUPT_BKPT;
    }
    rc = getPage(pBt, ovflPgno, &pOvfl, 0);
    if( rc ) return rc;
    ovflPgno = get4byte(pOvfl->aData);
    rc = freePage(pOvfl);
    sqlite3pager_unref(pOvfl->aData);
    if( rc ) return rc;
  }
  return SQLITE_OK;
................................................................................
      */
      if( pBt->autoVacuum && pgnoPtrmap!=0 && rc==SQLITE_OK ){
        rc = ptrmapPut(pBt, pgnoOvfl, PTRMAP_OVERFLOW2, pgnoPtrmap);
      }
#endif
      if( rc ){
        releasePage(pToRelease);

        return rc;
      }
      put4byte(pPrior, pgnoOvfl);
      releasePage(pToRelease);
      pToRelease = pOvfl;
      pPrior = pOvfl->aData;
      put4byte(pPrior, 0);
................................................................................
    ** case, then do not do the transfer.  Leave page 1 empty except
    ** for the right-pointer to the child page.  The child page becomes
    ** the virtual root of the tree.
    */
    pgnoChild = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    assert( pgnoChild>0 );
    assert( pgnoChild<=sqlite3pager_pagecount(pPage->pBt->pPager) );
    rc = getPage(pPage->pBt, pgnoChild, &pChild, 0);
    if( rc ) goto end_shallow_balance;
    if( pPage->pgno==1 ){
      rc = initPage(pChild, pPage);
      if( rc ) goto end_shallow_balance;
      assert( pChild->nOverflow==0 );
      if( pChild->nFree>=100 ){
        /* The child information will fit on the root page, so do the
................................................................................
    }

    if( pgnoMove!=pgnoRoot ){
      u8 eType;
      Pgno iPtrPage;

      releasePage(pPageMove);
      rc = getPage(pBt, pgnoRoot, &pRoot, 0);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = ptrmapGet(pBt, pgnoRoot, &eType, &iPtrPage);
      if( rc!=SQLITE_OK || eType==PTRMAP_ROOTPAGE || eType==PTRMAP_FREEPAGE ){
        releasePage(pRoot);
        return rc;
................................................................................
        return rc;
      }
      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove);
      releasePage(pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = getPage(pBt, pgnoRoot, &pRoot, 0);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = sqlite3pager_write(pRoot->aData);
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
................................................................................

  if( pgno>sqlite3pager_pagecount(pBt->pPager) ){
    return SQLITE_CORRUPT_BKPT;
  }

  rc = getAndInitPage(pBt, pgno, &pPage, pParent);
  if( rc ) goto cleardatabasepage_out;


  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
    if( !pPage->leaf ){
      rc = clearDatabasePage(pBt, get4byte(pCell), pPage->pParent, 1);
      if( rc ) goto cleardatabasepage_out;
    }
    rc = clearCell(pPage, pCell);
................................................................................
  }
  if( !pPage->leaf ){
    rc = clearDatabasePage(pBt, get4byte(&pPage->aData[8]), pPage->pParent, 1);
    if( rc ) goto cleardatabasepage_out;
  }
  if( freePageFlag ){
    rc = freePage(pPage);
  }else if( (rc = sqlite3pager_write(pPage->aData))==0 ){
    zeroPage(pPage, pPage->aData[0] | PTF_LEAF);
  }

cleardatabasepage_out:
  releasePage(pPage);
  return rc;
}
................................................................................
  ** root page. If an open cursor was using this page a problem would 
  ** occur.
  */
  if( pBt->pCursor ){
    return SQLITE_LOCKED;
  }

  rc = getPage(pBt, (Pgno)iTable, &pPage, 0);
  if( rc ) return rc;
  rc = sqlite3BtreeClearTable(p, iTable);
  if( rc ){
    releasePage(pPage);
    return rc;
  }

................................................................................
      }else{
        /* The table being dropped does not have the largest root-page
        ** number in the database. So move the page that does into the 
        ** gap left by the deleted root-page.
        */
        MemPage *pMove;
        releasePage(pPage);
        rc = getPage(pBt, maxRootPgno, &pMove, 0);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = relocatePage(pBt, pMove, PTRMAP_ROOTPAGE, 0, iTable);
        releasePage(pMove);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = getPage(pBt, maxRootPgno, &pMove, 0);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = freePage(pMove);
        releasePage(pMove);
        if( rc!=SQLITE_OK ){
          return rc;
................................................................................
  int hdr;
  int nCell;
  int isInit;
  unsigned char *data;
  char range[20];
  unsigned char payload[20];

  rc = getPage(pBt, (Pgno)pgno, &pPage, 0);
  isInit = pPage->isInit;
  if( pPage->isInit==0 ){
    initPage(pPage, pParent);
  }
  if( rc ){
    return rc;
  }
................................................................................

  /* Check that the page exists
  */
  pBt = pCheck->pBt;
  usableSize = pBt->usableSize;
  if( iPage==0 ) return 0;
  if( checkRef(pCheck, iPage, zParentContext) ) return 0;
  if( (rc = getPage(pBt, (Pgno)iPage, &pPage, 0))!=0 ){
    checkAppendMsg(pCheck, zContext,
       "unable to get the page. error code=%d", rc);
    return 0;
  }
  if( (rc = initPage(pPage, pParent))!=0 ){
    checkAppendMsg(pCheck, zContext, "initPage() returns error code %d", rc);
    releasePage(pPage);

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.284 2007/03/01 00:29:14 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>
................................................................................
** See also sqlite3pager_lookup().  Both this routine and _lookup() attempt
** to find a page in the in-memory cache first.  If the page is not already
** in memory, this routine goes to disk to read it in whereas _lookup()
** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** or journal files.





*/
int sqlite3pager_get(Pager *pPager, Pgno pgno, void **ppPage){
  PgHdr *pPg;
  int rc;

  /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
  ** number greater than this, or zero, is requested.
  */
  if( pgno>PAGER_MAX_PGNO || pgno==0 || pgno==PAGER_MJ_PGNO(pPager) ){
................................................................................
      rc = pPager->errCode;
      return rc;
    }

    /* Populate the page with data, either by reading from the database
    ** file, or by setting the entire page to zero.
    */
    if( sqlite3pager_pagecount(pPager)<(int)pgno || MEMDB ){


      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
    }else{
      assert( MEMDB==0 );
      rc = sqlite3OsSeek(pPager->fd, (pgno-1)*(i64)pPager->pageSize);
      if( rc==SQLITE_OK ){
        rc = sqlite3OsRead(pPager->fd, PGHDR_TO_DATA(pPg),
                              pPager->pageSize);

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.285 2007/03/04 13:15:28 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>
................................................................................
** See also sqlite3pager_lookup().  Both this routine and _lookup() attempt
** to find a page in the in-memory cache first.  If the page is not already
** in memory, this routine goes to disk to read it in whereas _lookup()
** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** or journal files.
**
** If clrFlag is false, the page contents are actually read from disk.
** If clfFlag is true, it means the page is about to be erased and
** rewritten without first being read so there is no point it doing
** the disk I/O.
*/
int sqlite3pager_acquire(Pager *pPager, Pgno pgno, void **ppPage, int clrFlag){
  PgHdr *pPg;
  int rc;

  /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
  ** number greater than this, or zero, is requested.
  */
  if( pgno>PAGER_MAX_PGNO || pgno==0 || pgno==PAGER_MJ_PGNO(pPager) ){
................................................................................
      rc = pPager->errCode;
      return rc;
    }

    /* Populate the page with data, either by reading from the database
    ** file, or by setting the entire page to zero.
    */
    if( sqlite3pager_pagecount(pPager)<(int)pgno || MEMDB
         || (clrFlag && !pPager->alwaysRollback) 
    ){
      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
    }else{
      assert( MEMDB==0 );
      rc = sqlite3OsSeek(pPager->fd, (pgno-1)*(i64)pPager->pageSize);
      if( rc==SQLITE_OK ){
        rc = sqlite3OsRead(pPager->fd, PGHDR_TO_DATA(pPg),
                              pPager->pageSize);

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.52 2006/11/06 21:20:26 drh Exp $
*/

#ifndef _PAGER_H_
#define _PAGER_H_

/*
** The default size of a database page.
................................................................................
void sqlite3pager_set_busyhandler(Pager*, BusyHandler *pBusyHandler);
void sqlite3pager_set_destructor(Pager*, void(*)(void*,int));
void sqlite3pager_set_reiniter(Pager*, void(*)(void*,int));
int sqlite3pager_set_pagesize(Pager*, int);
int sqlite3pager_read_fileheader(Pager*, int, unsigned char*);
void sqlite3pager_set_cachesize(Pager*, int);
int sqlite3pager_close(Pager *pPager);
int sqlite3pager_get(Pager *pPager, Pgno pgno, void **ppPage);

void *sqlite3pager_lookup(Pager *pPager, Pgno pgno);
int sqlite3pager_ref(void*);
int sqlite3pager_unref(void*);
Pgno sqlite3pager_pagenumber(void*);
int sqlite3pager_write(void*);
int sqlite3pager_iswriteable(void*);
int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void*);

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.53 2007/03/04 13:15:28 drh Exp $
*/

#ifndef _PAGER_H_
#define _PAGER_H_

/*
** The default size of a database page.
................................................................................
void sqlite3pager_set_busyhandler(Pager*, BusyHandler *pBusyHandler);
void sqlite3pager_set_destructor(Pager*, void(*)(void*,int));
void sqlite3pager_set_reiniter(Pager*, void(*)(void*,int));
int sqlite3pager_set_pagesize(Pager*, int);
int sqlite3pager_read_fileheader(Pager*, int, unsigned char*);
void sqlite3pager_set_cachesize(Pager*, int);
int sqlite3pager_close(Pager *pPager);
int sqlite3pager_acquire(Pager *pPager, Pgno pgno, void **ppPage, int clrFlag);
#define sqlite3pager_get(A,B,C) sqlite3pager_acquire(A,B,C,0)
void *sqlite3pager_lookup(Pager *pPager, Pgno pgno);
int sqlite3pager_ref(void*);
int sqlite3pager_unref(void*);
Pgno sqlite3pager_pagenumber(void*);
int sqlite3pager_write(void*);
int sqlite3pager_iswriteable(void*);
int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void*);