SQLite

  int nIgnore;

  pC = p->apCsr[pOp->p1];
  assert( isSorter(pC) );
  assert( pOp->p4type==P4_INT32 );
  pIn3 = &aMem[pOp->p3];
  nIgnore = pOp->p4.i;
  res = 0;
  rc = sqlite3VdbeSorterCompare(pC, pIn3, nIgnore, &res);
  VdbeBranchTaken(res!=0,2);
  if( res ){
    pc = pOp->p2-1;
  }
  break;
};

  assert( pOp->p1>=0 && pOp->p1<p->nCursor );
  pC = p->apCsr[pOp->p1];
  assert( pC!=0 );
  assert( isSorter(pC)==(pOp->opcode==OP_SorterSort) );
  res = 1;
  if( isSorter(pC) ){
    rc = sqlite3VdbeSorterRewind(pC, &res);
  }else{
    pCrsr = pC->pCursor;
    assert( pCrsr );
    rc = sqlite3BtreeFirst(pCrsr, &res);
    pC->deferredMoveto = 0;
    pC->cacheStatus = CACHE_STALE;
    pC->rowidIsValid = 0;

  pCrsr = pC->pCursor;
  if( pOp->p5 & OPFLAG_NCHANGE ) p->nChange++;
  assert( pCrsr!=0 );
  assert( pC->isTable==0 );
  rc = ExpandBlob(pIn2);
  if( rc==SQLITE_OK ){
    if( isSorter(pC) ){
      rc = sqlite3VdbeSorterWrite(pC, pIn2);
    }else{
      nKey = pIn2->n;
      zKey = pIn2->z;
      rc = sqlite3BtreeInsert(pCrsr, zKey, nKey, "", 0, 0, pOp->p3, 
          ((pOp->p5 & OPFLAG_USESEEKRESULT) ? pC->seekResult : 0)
          );
      assert( pC->deferredMoveto==0 );

int sqlite3VdbeTransferError(Vdbe *p);

int sqlite3VdbeSorterInit(sqlite3 *, int, VdbeCursor *);
void sqlite3VdbeSorterReset(sqlite3 *, VdbeSorter *);
void sqlite3VdbeSorterClose(sqlite3 *, VdbeCursor *);
int sqlite3VdbeSorterRowkey(const VdbeCursor *, Mem *);
int sqlite3VdbeSorterNext(sqlite3 *, const VdbeCursor *, int *);
int sqlite3VdbeSorterRewind(const VdbeCursor *, int *);
int sqlite3VdbeSorterWrite(const VdbeCursor *, Mem *);
int sqlite3VdbeSorterCompare(const VdbeCursor *, Mem *, int, int *);

#if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE>0
  void sqlite3VdbeEnter(Vdbe*);
  void sqlite3VdbeLeave(Vdbe*);
#else
# define sqlite3VdbeEnter(X)

**
** Or, if an error occurs, return an SQLite error code. The final value of
** *pp is undefined in this case.
*/
static int vdbeSorterMapFile(SortSubtask *pTask, SorterFile *pFile, u8 **pp){
  int rc = SQLITE_OK;
  if( pFile->iEof<=(i64)(pTask->pSorter->db->nMaxSorterMmap) ){
    rc = sqlite3OsFetch(pFile->pFd, 0, (int)pFile->iEof, (void**)pp);
  }
  return rc;
}

/*
** Seek iterator pIter to offset iOff within file pFile. Return SQLITE_OK 
** if successful, or an SQLite error code if an error occurs.

#ifdef SQLITE_DEBUG_SORTER_THREADS
static void vdbeSorterWorkDebug(SortSubtask *pTask, const char *zEvent){
  i64 t;
  int iTask = (pTask - pTask->pSorter->aTask);
  sqlite3OsCurrentTimeInt64(pTask->pSorter->db->pVfs, &t);
  fprintf(stderr, "%lld:%d %s\n", t, iTask, zEvent);
}
static void vdbeSorterRewindDebug(const char *zEvent){
  i64 t;
  sqlite3OsCurrentTimeInt64(sqlite3_vfs_find(0), &t);
  fprintf(stderr, "%lld:X %s\n", t, zEvent);
}
static void vdbeSorterPopulateDebug(
  SortSubtask *pTask,
  const char *zEvent
){
  i64 t;

    i64 t;
    sqlite3OsCurrentTimeInt64(pTask->pSorter->db->pVfs, &t);
    fprintf(stderr, "%lld:main %s\n", t, zEvent);
  }
}
#else
# define vdbeSorterWorkDebug(x,y)
# define vdbeSorterRewindDebug(y)
# define vdbeSorterPopulateDebug(x,y)
# define vdbeSorterBlockDebug(x,y,z)
#endif

#if SQLITE_MAX_WORKER_THREADS>0
/*
** Join thread pTask->thread.

** the specific VFS implementation.
*/
static void vdbeSorterExtendFile(sqlite3 *db, sqlite3_file *pFile, i64 nByte){
  if( nByte<=(i64)(db->nMaxSorterMmap) ){
    int rc = sqlite3OsTruncate(pFile, nByte);
    if( rc==SQLITE_OK ){
      void *p = 0;
      sqlite3OsFetch(pFile, 0, (int)nByte, &p);
      sqlite3OsUnfetch(pFile, 0, p);
    }
  }
}
#else
# define vdbeSorterExtendFile(x,y,z) SQLITE_OK
#endif

    }
    *pbEof = (pMerger->aIter[pMerger->aTree[1]].pFile==0);
  }

  return rc;
}

#if SQLITE_MAX_WORKER_THREADS>0
/*
** The main routine for background threads that write level-0 PMAs.
*/
static void *vdbeSorterFlushThread(void *pCtx){
  SortSubtask *pTask = (SortSubtask*)pCtx;
  int rc;                         /* Return code */
  assert( pTask->bDone==0 );
  rc = vdbeSorterListToPMA(pTask, &pTask->list);
  pTask->bDone = 1;
  return SQLITE_INT_TO_PTR(rc);
}
#endif /* SQLITE_MAX_WORKER_THREADS>0 */

/*
** Flush the current contents of VdbeSorter.list to a new PMA, possibly
** using a background thread.
*/
static int vdbeSorterFlushPMA(VdbeSorter *pSorter){
#if SQLITE_MAX_WORKER_THREADS==0

      }

      rc = vdbeSorterCreateThread(pTask, vdbeSorterFlushThread, pCtx);
    }
  }

  return rc;
#endif /* SQLITE_MAX_WORKER_THREADS!=0 */
}

/*
** Add a record to the sorter.
*/
int sqlite3VdbeSorterWrite(

  const VdbeCursor *pCsr,         /* Sorter cursor */
  Mem *pVal                       /* Memory cell containing record */
){
  VdbeSorter *pSorter = pCsr->pSorter;
  int rc = SQLITE_OK;             /* Return Code */
  SorterRecord *pNew;             /* New list element */

      );
      pSorter->list.aMemory = aNew;
      pSorter->nMemory = nNew;
    }

    pNew = (SorterRecord*)&pSorter->list.aMemory[pSorter->iMemory];
    pSorter->iMemory += ROUND8(nReq);
    pNew->u.iNext = (int)((u8*)(pSorter->list.pList) - pSorter->list.aMemory);
  }else{
    pNew = (SorterRecord *)sqlite3Malloc(nReq);
    if( pNew==0 ){
      return SQLITE_NOMEM;
    }
    pNew->u.pNext = pSorter->list.pList;
  }

  }else{
    vdbeMergeEngineFree(pMerger);
    rc = SQLITE_NOMEM;
  }
  return rc;
}

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

#define INCRINIT_NORMAL 0
#define INCRINIT_TASK   1
#define INCRINIT_ROOT   2
static int vdbePmaReaderIncrInit(PmaReader *pIter, int eMode);

/*

**
** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
*/
static int vdbeSorterSetupMerge(VdbeSorter *pSorter){
  int rc;                         /* Return code */
  SortSubtask *pTask0 = &pSorter->aTask[0];
  MergeEngine *pMain = 0;
#if SQLITE_MAX_WORKER_THREADS
  sqlite3 *db = pTask0->pSorter->db;
#endif

  rc = vdbeSorterMergeTreeBuild(pSorter, &pMain);
  if( rc==SQLITE_OK ){
#if SQLITE_MAX_WORKER_THREADS
    if( pSorter->bUseThreads ){
      int iTask;
      PmaReader *pIter;
      SortSubtask *pLast = &pSorter->aTask[pSorter->nTask-1];
      rc = vdbeSortAllocUnpacked(pLast);
      if( rc==SQLITE_OK ){
        pIter = (PmaReader*)sqlite3DbMallocZero(db, sizeof(PmaReader));
        pSorter->pReader = pIter;
      }

/*
** Once the sorter has been populated by calls to sqlite3VdbeSorterWrite,
** this function is called to prepare for iterating through the records
** in sorted order.
*/
int sqlite3VdbeSorterRewind(const VdbeCursor *pCsr, int *pbEof){
  VdbeSorter *pSorter = pCsr->pSorter;
  int rc = SQLITE_OK;             /* Return code */

  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

  if( pSorter->list.pList ){
    rc = vdbeSorterFlushPMA(pSorter);
  }

  /* Join all threads */
  rc = vdbeSorterJoinAll(pSorter, rc);

  vdbeSorterRewindDebug("rewind");

  /* Assuming no errors have occurred, set up a merger structure to 
  ** incrementally read and merge all remaining PMAs.  */
  assert( pSorter->pReader==0 );
  if( rc==SQLITE_OK ){
    rc = vdbeSorterSetupMerge(pSorter);
    *pbEof = 0;
  }

  vdbeSorterRewindDebug("rewinddone");
  return rc;
}

/*
** Advance to the next element in the sorter.
*/
int sqlite3VdbeSorterNext(sqlite3 *db, const VdbeCursor *pCsr, int *pbEof){