SQLite

    
    /* If eMode==BTALLOC_EXACT and a query of the pointer-map
    ** shows that the page 'nearby' is somewhere on the free-list, then
    ** the entire-list will be searched for that page.
    */
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( eMode==BTALLOC_EXACT ){
      if( nearby<=mxPage ){
        u8 eType;
        assert( nearby>0 );
        assert( pBt->autoVacuum );
        rc = ptrmapGet(pBt, nearby, &eType, 0);
        if( rc ) return rc;
        if( eType==PTRMAP_FREEPAGE ){
          searchList = 1;

  int rc;                             /* Return Code */
  u32 nFree;                          /* Initial number of pages on free-list */

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( CORRUPT_DB || iPage>1 );
  assert( !pMemPage || pMemPage->pgno==iPage );

  if( iPage<2 || iPage>pBt->nPage ){
    return SQLITE_CORRUPT_BKPT;
  }
  if( pMemPage ){
    pPage = pMemPage;
    sqlite3PagerRef(pPage->pDbPage);
  }else{
    pPage = btreePageLookup(pBt, iPage);

    /* The new root-page may not be allocated on a pointer-map page, or the
    ** PENDING_BYTE page.
    */
    while( pgnoRoot==PTRMAP_PAGENO(pBt, pgnoRoot) ||
        pgnoRoot==PENDING_BYTE_PAGE(pBt) ){
      pgnoRoot++;
    }
    assert( pgnoRoot>=3 || CORRUPT_DB );
    testcase( pgnoRoot<3 );

    /* Allocate a page. The page that currently resides at pgnoRoot will
    ** be moved to the allocated page (unless the allocated page happens
    ** to reside at pgnoRoot).
    */
    rc = allocateBtreePage(pBt, &pPageMove, &pgnoMove, pgnoRoot, BTALLOC_EXACT);
    if( rc!=SQLITE_OK ){

** Also write code to modify the sqlite_schema table and internal schema
** if a root-page of another table is moved by the btree-layer whilst
** erasing iTable (this can happen with an auto-vacuum database).
*/ 
static void destroyRootPage(Parse *pParse, int iTable, int iDb){
  Vdbe *v = sqlite3GetVdbe(pParse);
  int r1 = sqlite3GetTempReg(pParse);
  if( iTable<2 ) sqlite3ErrorMsg(pParse, "corrupt schema");
  sqlite3VdbeAddOp3(v, OP_Destroy, iTable, r1, iDb);
  sqlite3MayAbort(pParse);
#ifndef SQLITE_OMIT_AUTOVACUUM
  /* OP_Destroy stores an in integer r1. If this integer
  ** is non-zero, then it is the root page number of a table moved to
  ** location iTable. The following code modifies the sqlite_schema table to
  ** reflect this.

    Index *pIndex;
    pIndex = sqlite3FindIndex(db, argv[1], db->aDb[iDb].zDbSName);
    if( pIndex==0 ){
      corruptSchema(pData, argv[1], "orphan index");
    }else
    if( sqlite3GetUInt32(argv[3],&pIndex->tnum)==0
     || pIndex->tnum<2
     || (pIndex->tnum>pData->mxPage && pData->mxPage!=0)
     || sqlite3IndexHasDuplicateRootPage(pIndex)
    ){
      if( sqlite3Config.bExtraSchemaChecks ){
        corruptSchema(pData, argv[1], "invalid rootpage");
      }
    }
  }

/*
** Return a 32-bit integer value extracted from a string.  If the
** string is not an integer, just return 0.
*/
int sqlite3Atoi(const char *z){
  int x = 0;
  if( z ) sqlite3GetInt32(z, &x);
  return x;
}

/*
** Try to convert z into an unsigned 32-bit integer.  Return true on
** success and false if there is an error.
**