vdbeSorterWorkDebug(pTask, "exit");
  assert( rc!=SQLITE_OK || pList->pList==0 );
  assert( rc!=SQLITE_OK || pTask->file.iEof==iSz );
  return rc;
}

/*
** Advance the MergeEngine pMerge (passed as the second argument) to
** its next entry.  Set *pbEof to true there is no next entry because
** the MergeEngine has reached the end of all its inputs.
**
** Return SQLITE_OK if successful or an error code if an error occurs.
*/
static int vdbeMergeEngineStep(
  SortSubtask *pTask,        /* The thread in which this MergeEngine runs */
  MergeEngine *pMerger,      /* The merge engine to advance to the next row */
  int *pbEof                 /* Set TRUE at EOF.  Set false for more content */
){
  int rc;
  int iPrev = pMerger->aTree[1];/* Index of PmaReader to advance */

  /* A MergeEngine object is only used by a single thread */
  assert( pMerger->pTask==0 || pMerger->pTask==pTask );
  pMerger->pTask = pTask;

  /* Advance the current PmaReader */
  rc = vdbePmaReaderNext(&pMerger->aReadr[iPrev]);

  /* Update contents of aTree[] */
  if( rc==SQLITE_OK ){
    int i;                      /* Index of aTree[] to recalculate */
................................................................................
    ** In either case exit the loop. */
    if( pReader->pFd==0 ) break;
    if( (iEof + nKey + sqlite3VarintLen(nKey))>(iStart + pIncr->mxSz) ) break;

    /* Write the next key to the output. */
    vdbePmaWriteVarint(&writer, nKey);
    vdbePmaWriteBlob(&writer, pReader->aKey, nKey);

    rc = vdbeMergeEngineStep(pTask, pIncr->pMerger, &dummy);
  }

  rc2 = vdbePmaWriterFinish(&writer, &pOut->iEof);
  if( rc==SQLITE_OK ) rc = rc2;
  vdbeSorterPopulateDebug(pTask, "exit");
  return rc;
}
................................................................................

/*
** Allocate and return a new IncrMerger object to read data from pMerger.
**
** If an OOM condition is encountered, return NULL. In this case free the
** pMerger argument before returning.
*/
static int vdbeIncrNew(
  SortSubtask *pTask,     /* The thread that will be using the new IncrMerger */
  MergeEngine *pMerger,   /* The MergeEngine that the IncrMerger will control */
  IncrMerger **ppOut      /* Write the new IncrMerger here */
){
  int rc = SQLITE_OK;
  IncrMerger *pIncr = *ppOut = (IncrMerger*)
       (sqlite3FaultSim(100) ? 0 : sqlite3MallocZero(sizeof(*pIncr)));
................................................................................
  return rc;
}

#if SQLITE_MAX_WORKER_THREADS>0
/*
** Set the "use-threads" flag on object pIncr.
*/
static void vdbeIncrSetThreads(IncrMerger *pIncr){
  pIncr->bUseThread = 1;
  pIncr->pTask->file2.iEof -= pIncr->mxSz;
}
#endif /* SQLITE_MAX_WORKER_THREADS>0 */



................................................................................
  int eMode                       /* One of the INCRINIT_XXX constants */
){
  int rc = SQLITE_OK;             /* Return code */
  int i;                          /* For looping over PmaReader objects */
  int nTree = pMerger->nTree;

  /* Verify that the MergeEngine is assigned to a single thread */
  assert( pMerger->pTask==0 || pMerger->pTask==pTask );
  pMerger->pTask = pTask;

  for(i=0; i<nTree; i++){
    if( eMode==INCRINIT_ROOT ){
      /* PmaReaders should be normally initialized in order, as if they are
      ** reading from the same temp file this makes for more linear file IO.
      ** However, in the INCRINIT_ROOT case, if PmaReader aReadr[nTask-1] is
................................................................................
){
  int rc = SQLITE_OK;
  int nDiv = 1;
  int i;
  MergeEngine *p = pRoot;
  IncrMerger *pIncr;

  rc = vdbeIncrNew(pTask, pLeaf, &pIncr);

  for(i=1; i<nDepth; i++){
    nDiv = nDiv * SORTER_MAX_MERGE_COUNT;
  }

  for(i=1; i<nDepth && rc==SQLITE_OK; i++){
    int iIter = (iSeq / nDiv) % SORTER_MAX_MERGE_COUNT;
................................................................................
    PmaReader *pReadr = &p->aReadr[iIter];

    if( pReadr->pIncr==0 ){
      MergeEngine *pNew = vdbeMergeEngineNew(SORTER_MAX_MERGE_COUNT);
      if( pNew==0 ){
        rc = SQLITE_NOMEM;
      }else{
        rc = vdbeIncrNew(pTask, pNew, &pReadr->pIncr);
      }
    }
    if( rc==SQLITE_OK ){
      p = pReadr->pIncr->pMerger;
      nDiv = nDiv / SORTER_MAX_MERGE_COUNT;
    }
  }
................................................................................
          }
        }
      }

      if( rc==SQLITE_OK ){
#if SQLITE_MAX_WORKER_THREADS>0
        if( pMain!=0 ){
          rc = vdbeIncrNew(pTask, pRoot, &pMain->aReadr[iTask].pIncr);
        }else
#endif
        {
          assert( pMain==0 );
          pMain = pRoot;
        }
      }else{
................................................................................
      rc = vdbeSortAllocUnpacked(pLast);
      if( rc==SQLITE_OK ){
        pReadr = (PmaReader*)sqlite3DbMallocZero(db, sizeof(PmaReader));
        pSorter->pReader = pReadr;
        if( pReadr==0 ) rc = SQLITE_NOMEM;
      }
      if( rc==SQLITE_OK ){
        rc = vdbeIncrNew(pLast, pMain, &pReadr->pIncr);
        if( rc==SQLITE_OK ){
          vdbeIncrSetThreads(pReadr->pIncr);
          for(iTask=0; iTask<(pSorter->nTask-1); iTask++){
            IncrMerger *pIncr;
            if( (pIncr = pMain->aReadr[iTask].pIncr) ){
              vdbeIncrSetThreads(pIncr);
              assert( pIncr->pTask!=pLast );
            }
          }
          for(iTask=0; rc==SQLITE_OK && iTask<pSorter->nTask; iTask++){
            PmaReader *p = &pMain->aReadr[iTask];
            assert( p->pIncr==0 || p->pIncr->pTask==&pSorter->aTask[iTask] );
            if( p->pIncr ){ 
................................................................................
#if SQLITE_MAX_WORKER_THREADS>0
    if( pSorter->bUseThreads ){
      rc = vdbePmaReaderNext(pSorter->pReader);
      *pbEof = (pSorter->pReader->pFd==0);
    }else
#endif
    /*if( !pSorter->bUseThreads )*/ {

      rc = vdbeMergeEngineStep(&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);
    *pbEof = !pSorter->list.pList;

  vdbeSorterWorkDebug(pTask, "exit");
  assert( rc!=SQLITE_OK || pList->pList==0 );
  assert( rc!=SQLITE_OK || pTask->file.iEof==iSz );
  return rc;
}

/*
** Advance the MergeEngine to its next entry.
** Set *pbEof to true there is no next entry because
** the MergeEngine has reached the end of all its inputs.
**
** Return SQLITE_OK if successful or an error code if an error occurs.
*/
static int vdbeMergeEngineStep(

  MergeEngine *pMerger,      /* The merge engine to advance to the next row */
  int *pbEof                 /* Set TRUE at EOF.  Set false for more content */
){
  int rc;
  int iPrev = pMerger->aTree[1];/* Index of PmaReader to advance */



  SortSubtask *pTask = pMerger->pTask;

  /* Advance the current PmaReader */
  rc = vdbePmaReaderNext(&pMerger->aReadr[iPrev]);

  /* Update contents of aTree[] */
  if( rc==SQLITE_OK ){
    int i;                      /* Index of aTree[] to recalculate */
................................................................................
    ** In either case exit the loop. */
    if( pReader->pFd==0 ) break;
    if( (iEof + nKey + sqlite3VarintLen(nKey))>(iStart + pIncr->mxSz) ) break;

    /* Write the next key to the output. */
    vdbePmaWriteVarint(&writer, nKey);
    vdbePmaWriteBlob(&writer, pReader->aKey, nKey);
    assert( pIncr->pMerger->pTask==pTask );
    rc = vdbeMergeEngineStep(pIncr->pMerger, &dummy);
  }

  rc2 = vdbePmaWriterFinish(&writer, &pOut->iEof);
  if( rc==SQLITE_OK ) rc = rc2;
  vdbeSorterPopulateDebug(pTask, "exit");
  return rc;
}
................................................................................

/*
** Allocate and return a new IncrMerger object to read data from pMerger.
**
** If an OOM condition is encountered, return NULL. In this case free the
** pMerger argument before returning.
*/
static int vdbeIncrMergerNew(
  SortSubtask *pTask,     /* The thread that will be using the new IncrMerger */
  MergeEngine *pMerger,   /* The MergeEngine that the IncrMerger will control */
  IncrMerger **ppOut      /* Write the new IncrMerger here */
){
  int rc = SQLITE_OK;
  IncrMerger *pIncr = *ppOut = (IncrMerger*)
       (sqlite3FaultSim(100) ? 0 : sqlite3MallocZero(sizeof(*pIncr)));
................................................................................
  return rc;
}

#if SQLITE_MAX_WORKER_THREADS>0
/*
** Set the "use-threads" flag on object pIncr.
*/
static void vdbeIncrMergerSetThreads(IncrMerger *pIncr){
  pIncr->bUseThread = 1;
  pIncr->pTask->file2.iEof -= pIncr->mxSz;
}
#endif /* SQLITE_MAX_WORKER_THREADS>0 */



................................................................................
  int eMode                       /* One of the INCRINIT_XXX constants */
){
  int rc = SQLITE_OK;             /* Return code */
  int i;                          /* For looping over PmaReader objects */
  int nTree = pMerger->nTree;

  /* Verify that the MergeEngine is assigned to a single thread */
  assert( pMerger->pTask==0 ); // || pMerger->pTask==pTask );
  pMerger->pTask = pTask;

  for(i=0; i<nTree; i++){
    if( eMode==INCRINIT_ROOT ){
      /* PmaReaders should be normally initialized in order, as if they are
      ** reading from the same temp file this makes for more linear file IO.
      ** However, in the INCRINIT_ROOT case, if PmaReader aReadr[nTask-1] is
................................................................................
){
  int rc = SQLITE_OK;
  int nDiv = 1;
  int i;
  MergeEngine *p = pRoot;
  IncrMerger *pIncr;

  rc = vdbeIncrMergerNew(pTask, pLeaf, &pIncr);

  for(i=1; i<nDepth; i++){
    nDiv = nDiv * SORTER_MAX_MERGE_COUNT;
  }

  for(i=1; i<nDepth && rc==SQLITE_OK; i++){
    int iIter = (iSeq / nDiv) % SORTER_MAX_MERGE_COUNT;
................................................................................
    PmaReader *pReadr = &p->aReadr[iIter];

    if( pReadr->pIncr==0 ){
      MergeEngine *pNew = vdbeMergeEngineNew(SORTER_MAX_MERGE_COUNT);
      if( pNew==0 ){
        rc = SQLITE_NOMEM;
      }else{
        rc = vdbeIncrMergerNew(pTask, pNew, &pReadr->pIncr);
      }
    }
    if( rc==SQLITE_OK ){
      p = pReadr->pIncr->pMerger;
      nDiv = nDiv / SORTER_MAX_MERGE_COUNT;
    }
  }
................................................................................
          }
        }
      }

      if( rc==SQLITE_OK ){
#if SQLITE_MAX_WORKER_THREADS>0
        if( pMain!=0 ){
          rc = vdbeIncrMergerNew(pTask, pRoot, &pMain->aReadr[iTask].pIncr);
        }else
#endif
        {
          assert( pMain==0 );
          pMain = pRoot;
        }
      }else{
................................................................................
      rc = vdbeSortAllocUnpacked(pLast);
      if( rc==SQLITE_OK ){
        pReadr = (PmaReader*)sqlite3DbMallocZero(db, sizeof(PmaReader));
        pSorter->pReader = pReadr;
        if( pReadr==0 ) rc = SQLITE_NOMEM;
      }
      if( rc==SQLITE_OK ){
        rc = vdbeIncrMergerNew(pLast, pMain, &pReadr->pIncr);
        if( rc==SQLITE_OK ){
          vdbeIncrMergerSetThreads(pReadr->pIncr);
          for(iTask=0; iTask<(pSorter->nTask-1); iTask++){
            IncrMerger *pIncr;
            if( (pIncr = pMain->aReadr[iTask].pIncr) ){
              vdbeIncrMergerSetThreads(pIncr);
              assert( pIncr->pTask!=pLast );
            }
          }
          for(iTask=0; rc==SQLITE_OK && iTask<pSorter->nTask; iTask++){
            PmaReader *p = &pMain->aReadr[iTask];
            assert( p->pIncr==0 || p->pIncr->pTask==&pSorter->aTask[iTask] );
            if( p->pIncr ){ 
................................................................................
#if SQLITE_MAX_WORKER_THREADS>0
    if( pSorter->bUseThreads ){
      rc = vdbePmaReaderNext(pSorter->pReader);
      *pbEof = (pSorter->pReader->pFd==0);
    }else
#endif
    /*if( !pSorter->bUseThreads )*/ {
      assert( pSorter->pMerger->pTask==(&pSorter->aTask[0]) );
      rc = vdbeMergeEngineStep(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);
    *pbEof = !pSorter->list.pList;