SQLite

    case SQLITE_CONFIG_WIN32_HEAPSIZE: {
      sqlite3GlobalConfig.nHeap = va_arg(ap, int);
      break;
    }
#endif

    case SQLITE_CONFIG_WORKER_THREADS: {
#if SQLITE_MAX_WORKER_THREADS>0
      int n = va_arg(ap, int);
      if( n>SQLITE_MAX_WORKER_THREADS ) n = SQLITE_MAX_WORKER_THREADS;
      if( n>=0 ) sqlite3GlobalConfig.nWorker = n;
#endif
      break;
    }

    default: {
      rc = SQLITE_ERROR;
      break;
    }

** Free all memory belonging to the PmaReader object passed as the second
** argument. All structure fields are set to zero before returning.
*/
static void vdbePmaReaderClear(PmaReader *pIter){
  sqlite3_free(pIter->aAlloc);
  sqlite3_free(pIter->aBuffer);
  if( pIter->aMap ) sqlite3OsUnfetch(pIter->pFile, 0, pIter->aMap);
  vdbeIncrFree(pIter->pIncr);
  memset(pIter, 0, sizeof(PmaReader));
}

/*
** Read nByte bytes of data from the stream of data iterated by object p.
** If successful, set *ppOut to point to a buffer containing the data
** and return SQLITE_OK. Otherwise, if an error occurs, return an SQLite

  int i;                          /* Used to iterate through aTask[] */
  int mxCache;                    /* Cache size */
  VdbeSorter *pSorter;            /* The new sorter */
  KeyInfo *pKeyInfo;              /* Copy of pCsr->pKeyInfo with db==0 */
  int szKeyInfo;                  /* Size of pCsr->pKeyInfo in bytes */
  int sz;                         /* Size of pSorter in bytes */
  int rc = SQLITE_OK;
#if SQLITE_MAX_WORKER_THREADS==0
  const int nWorker = 0;
#else
  int nWorker = (sqlite3GlobalConfig.bCoreMutex?sqlite3GlobalConfig.nWorker:0);
#endif

  assert( pCsr->pKeyInfo && pCsr->pBt==0 );
  szKeyInfo = sizeof(KeyInfo) + (pCsr->pKeyInfo->nField-1)*sizeof(CollSeq*);
  sz = sizeof(VdbeSorter) + nWorker * sizeof(SortSubtask);

  pSorter = (VdbeSorter*)sqlite3DbMallocZero(db, sz + szKeyInfo);
  pCsr->pSorter = pSorter;

    if( !sqlite3TempInMemory(db) ){
      pSorter->mnPmaSize = SORTER_MIN_WORKING * pgsz;
      mxCache = db->aDb[0].pSchema->cache_size;
      if( mxCache<SORTER_MIN_WORKING ) mxCache = SORTER_MIN_WORKING;
      pSorter->mxPmaSize = mxCache * pgsz;

      /* If the application has not configure scratch memory using
      ** SQLITE_CONFIG_SCRATCH then we assume it is OK to do large memory
      ** allocations.  If scratch memory has been configured, then assume
      ** large memory allocations should be avoided to prevent heap
      ** fragmentation.
      */
      if( sqlite3GlobalConfig.pScratch==0 ){
        assert( pSorter->iMemory==0 );
        pSorter->nMemory = pgsz;
        pSorter->list.aMemory = (u8*)sqlite3Malloc(pgsz);
        if( !pSorter->list.aMemory ) rc = SQLITE_NOMEM;
      }
    }
  }

    rc = vdbeIncrInitMerger(pTask, pIncr->pMerger, eMode);

    /* Set up the required files for pIncr. A multi-theaded IncrMerge object
    ** requires two temp files to itself, whereas a single-threaded object
    ** only requires a region of pTask->file2. */
    if( rc==SQLITE_OK ){
      int mxSz = pIncr->mxSz;
#if SQLITE_MAX_WORKER_THREADS>0
      if( pIncr->bUseThread ){
        rc = vdbeSorterOpenTempFile(db, mxSz, &pIncr->aFile[0].pFd);
        if( rc==SQLITE_OK ){
          rc = vdbeSorterOpenTempFile(db, mxSz, &pIncr->aFile[1].pFd);
        }
      }else
#endif
      /*if( !pIncr->bUseThread )*/{
        if( pTask->file2.pFd==0 ){
          assert( pTask->file2.iEof>0 );
          rc = vdbeSorterOpenTempFile(db, pTask->file2.iEof, &pTask->file2.pFd);
          pTask->file2.iEof = 0;
        }
        if( rc==SQLITE_OK ){
          pIncr->aFile[1].pFd = pTask->file2.pFd;
          pIncr->iStartOff = pTask->file2.iEof;
          pTask->file2.iEof += mxSz;
        }





      }
    }

#if SQLITE_MAX_WORKER_THREADS>0
    if( rc==SQLITE_OK && pIncr->bUseThread ){
      /* Use the current thread to populate aFile[1], even though this
      ** iterator is multi-threaded. The reason being that this function
      ** is already running in background thread pIncr->pTask->thread. */
      assert( eMode==INCRINIT_ROOT || eMode==INCRINIT_TASK );
      rc = vdbeIncrPopulate(pIncr);
    }
#endif

    if( rc==SQLITE_OK && eMode!=INCRINIT_TASK ){
      rc = vdbePmaReaderNext(pIter);
    }
  }
  return rc;
}

** of *ppOut is undefined.
*/
static int vdbeSorterMergeTreeBuild(VdbeSorter *pSorter, MergeEngine **ppOut){
  MergeEngine *pMain = 0;
  int rc = SQLITE_OK;
  int iTask;

#if SQLITE_MAX_WORKER_THREADS>0
  /* If the sorter uses more than one task, then create the top-level 
  ** MergeEngine here. This MergeEngine will read data from exactly 
  ** one PmaReader per sub-task.  */
  assert( pSorter->bUseThreads || pSorter->nTask==1 );
  if( pSorter->nTask>1 ){
    pMain = vdbeMergeEngineNew(pSorter->nTask);
    if( pMain==0 ) rc = SQLITE_NOMEM;
  }
#endif

  for(iTask=0; iTask<pSorter->nTask && rc==SQLITE_OK; iTask++){
    SortSubtask *pTask = &pSorter->aTask[iTask];
    if( pTask->nPMA ){
      MergeEngine *pRoot = 0;     /* Root node of tree for this task */
      int nDepth = vdbeSorterTreeDepth(pTask->nPMA);
      i64 iReadOff = 0;

  int rc;                         /* Return code */

  assert( pSorter->bUsePMA || (pSorter->pReader==0 && pSorter->pMerger==0) );
  if( pSorter->bUsePMA ){
    assert( pSorter->pReader==0 || pSorter->pMerger==0 );
    assert( pSorter->bUseThreads==0 || pSorter->pReader );
    assert( pSorter->bUseThreads==1 || pSorter->pMerger );
#if SQLITE_MAX_WORKER_THREADS>0
    if( pSorter->bUseThreads ){
      rc = vdbePmaReaderNext(pSorter->pReader);
      *pbEof = (pSorter->pReader->pFile==0);
    }else
#endif
    /*if( !pSorter->bUseThreads )*/ {
      rc = vdbeSorterNext(&pSorter->aTask[0], pSorter->pMerger, pbEof);
    }
  }else{
    SorterRecord *pFree = pSorter->list.pList;
    pSorter->list.pList = pFree->u.pNext;
    pFree->u.pNext = 0;
    if( pSorter->list.aMemory==0 ) vdbeSorterRecordFree(db, pFree);

*/
static void *vdbeSorterRowkey(
  const VdbeSorter *pSorter,      /* Sorter object */
  int *pnKey                      /* OUT: Size of current key in bytes */
){
  void *pKey;
  if( pSorter->bUsePMA ){
    PmaReader *pReader;
#if SQLITE_MAX_WORKER_THREADS>0
    if( pSorter->bUseThreads ){
      pReader = pSorter->pReader;
    }else
#endif
    /*if( !pSorter->bUseThreads )*/{
      pReader = &pSorter->pMerger->aIter[pSorter->pMerger->aTree[1]];

    }
    *pnKey = pReader->nKey;
    pKey = pReader->aKey;
  }else{
    *pnKey = pSorter->list.pList->nVal;
    pKey = SRVAL(pSorter->list.pList);
  }
  return pKey;