SQLite

  sqlite3_file *pTemp2 = 0;       /* Second temp file to use */
  i64 iWrite2 = 0;                /* Write offset for pTemp2 */
  int nIter;                      /* Number of iterators used */
  int nByte;                      /* Bytes of space required for aIter/aTree */
  int N = 2;                      /* Power of 2 >= nIter */

  assert( pSorter );

  /* If no data has been written to disk, then do not do so now. Instead,
  ** sort the VdbeSorter.pRecord list. The vdbe layer will read data directly
  ** from the in-memory list.  */
  if( pSorter->nPMA==0 ){
    *pbEof = !pSorter->pRecord;
    assert( pSorter->aTree==0 );
    return vdbeSorterSort(db, pCsr);
  }

  /* Write the current b-tree to a PMA. Close the b-tree cursor. */
  rc = vdbeSorterListToPMA(db, pCsr);
  if( rc!=SQLITE_OK ) return rc;





  /* Allocate space for aIter[] and aTree[]. */
  nIter = pSorter->nPMA;
  if( nIter>SORTER_MAX_MERGE_COUNT ) nIter = SORTER_MAX_MERGE_COUNT;
  assert( nIter>0 );
  while( N<nIter ) N += N;
  nByte = N * (sizeof(int) + sizeof(VdbeSorterIter));

}

/*
** Advance to the next element in the sorter.
*/
int sqlite3VdbeSorterNext(sqlite3 *db, VdbeCursor *pCsr, int *pbEof){
  VdbeSorter *pSorter = pCsr->pSorter;
  int rc;                         /* Return code */

  if( pSorter->aTree ){
    int iPrev = pSorter->aTree[1];/* Index of iterator to advance */
    int i;                        /* Index of aTree[] to recalculate */


    rc = vdbeSorterIterNext(db, &pSorter->aIter[iPrev]);
    for(i=(pSorter->nTree+iPrev)/2; rc==SQLITE_OK && i>0; i=i/2){
      rc = vdbeSorterDoCompare(pCsr, i);
    }

    *pbEof = (pSorter->aIter[pSorter->aTree[1]].pFile==0);
  }else{
    SorterRecord *pFree = pSorter->pRecord;
    pSorter->pRecord = pFree->pNext;
    pFree->pNext = 0;
    vdbeSorterRecordFree(db, pFree);
    *pbEof = !pSorter->pRecord;
    rc = SQLITE_OK;
  }
  return rc;
}

/*
** Return a pointer to a buffer owned by the sorter that contains the 
** current key.
*/
static void *vdbeSorterRowkey(
  VdbeSorter *pSorter,            /* Sorter object */
  int *pnKey                      /* OUT: Size of current key in bytes */
){
  void *pKey;
  if( pSorter->aTree ){
    VdbeSorterIter *pIter;
    pIter = &pSorter->aIter[ pSorter->aTree[1] ];
    *pnKey = pIter->nKey;
    pKey = pIter->aKey;
  }else{
    *pnKey = pSorter->pRecord->nVal;
    pKey = pSorter->pRecord->pVal;
  }
  return pKey;
}

/*
** Copy the current sorter key into the memory cell pOut.
*/
int sqlite3VdbeSorterRowkey(VdbeCursor *pCsr, Mem *pOut){
  VdbeSorter *pSorter = pCsr->pSorter;
  void *pKey; int nKey;           /* Sorter key to copy into pOut */

  pKey = vdbeSorterRowkey(pSorter, &nKey);
  if( sqlite3VdbeMemGrow(pOut, nKey, 0) ){
    return SQLITE_NOMEM;
  }
  pOut->n = nKey;
  MemSetTypeFlag(pOut, MEM_Blob);
  memcpy(pOut->z, pKey, nKey);

  return SQLITE_OK;
}

/*
** Compare the key in memory cell pVal with the key that the sorter cursor
** passed as the first argument currently points to. For the purposes of

int sqlite3VdbeSorterCompare(
  VdbeCursor *pCsr,               /* Sorter cursor */
  Mem *pVal,                      /* Value to compare to current sorter key */
  int *pRes                       /* OUT: Result of comparison */
){
  int rc;
  VdbeSorter *pSorter = pCsr->pSorter;
  void *pKey; int nKey;           /* Sorter key to compare pVal with */

  pKey = vdbeSorterRowkey(pSorter, &nKey);
  rc = vdbeSorterCompare(pCsr->pKeyInfo, 1, pVal->z, pVal->n, pKey, nKey, pRes);


  assert( rc!=SQLITE_OK || *pRes<=0 );
  return rc;
}

#endif /* #ifndef SQLITE_OMIT_MERGE_SORT */