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Overview
Comment:Allow the sorter to begin returning data to the VDBE as soon as it is available, instead of waiting until all keys have been sorted.
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SHA1:cb0ab20c48962cdee03115efa93d7d501780ac73
User & Date: dan 2014-04-14 19:23:18
Context
2014-04-15
19:52
Fix further code and documentation issues in vdbesort.c. check-in: d03f5b86 user: dan tags: threads
2014-04-14
19:23
Allow the sorter to begin returning data to the VDBE as soon as it is available, instead of waiting until all keys have been sorted. check-in: cb0ab20c user: dan tags: threads
18:41
Improve performance in single-threaded mode by having the final merge pass keys directly to the VDBE, instead of going via a final PMA. Closed-Leaf check-in: 02610cd9 user: dan tags: threads-experimental
2014-04-04
22:44
Fix harmless compiler warnings. check-in: e54dded2 user: drh tags: threads
Changes
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Changes to src/shell.c.

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  memcpy(data->separator,"|", 2);
  data->showHeader = 0;
  sqlite3_config(SQLITE_CONFIG_URI, 1);
  sqlite3_config(SQLITE_CONFIG_LOG, shellLog, data);
  sqlite3_snprintf(sizeof(mainPrompt), mainPrompt,"sqlite> ");
  sqlite3_snprintf(sizeof(continuePrompt), continuePrompt,"   ...> ");
  sqlite3_config(SQLITE_CONFIG_MULTITHREAD);
  sqlite3_config(SQLITE_CONFIG_WORKER_THREADS, 3);
}

/*
** Output text to the console in a font that attracts extra attention.
*/
#ifdef _WIN32
static void printBold(const char *zText){







|







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  memcpy(data->separator,"|", 2);
  data->showHeader = 0;
  sqlite3_config(SQLITE_CONFIG_URI, 1);
  sqlite3_config(SQLITE_CONFIG_LOG, shellLog, data);
  sqlite3_snprintf(sizeof(mainPrompt), mainPrompt,"sqlite> ");
  sqlite3_snprintf(sizeof(continuePrompt), continuePrompt,"   ...> ");
  sqlite3_config(SQLITE_CONFIG_MULTITHREAD);
  sqlite3_config(SQLITE_CONFIG_WORKER_THREADS, 4);
}

/*
** Output text to the console in a font that attracts extra attention.
*/
#ifdef _WIN32
static void printBold(const char *zText){

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** algorithm might be performed in parallel by separate threads.  Threads
** are only used when one or more PMA spill to disk.  If the sort is small
** enough to fit entirely in memory, everything happens on the main thread.
*/
#include "sqliteInt.h"
#include "vdbeInt.h"










/*
** Private objects used by the sorter
*/
typedef struct MergeEngine MergeEngine;     /* Merge PMAs together */
typedef struct PmaReader PmaReader;         /* Incrementally read one PMA */
typedef struct PmaWriter PmaWriter;         /* Incrementally write on PMA */
typedef struct SorterRecord SorterRecord;   /* A record being sorted */
typedef struct SortSubtask SortSubtask;     /* A sub-task in the sort process */














/*
** Candidate values for SortSubtask.eWork


















*/
#define SORT_SUBTASK_SORT   1     /* Sort records on pList */
#define SORT_SUBTASK_TO_PMA 2     /* Xfer pList to Packed-Memory-Array pTemp1 */
#define SORT_SUBTASK_CONS   3     /* Consolidate multiple PMAs */











/*
** Sorting is divided up into smaller subtasks.  Each subtask is controlled
** by an instance of this object. A Subtask might run in either the main thread
** or in a background thread.
**
** Exactly VdbeSorter.nTask instances of this object are allocated
................................................................................
**     the temp file if it is not already open.
**
**   SORT_SUBTASK_CONS:
**     Merge existing PMAs until SortSubtask.nConsolidate or fewer
**     remain in temp file SortSubtask.pTemp1.
*/
struct SortSubtask {
  SQLiteThread *pThread;          /* Thread handle, or NULL */
  int bDone;                      /* Set to true by pTask when finished */

  sqlite3 *db;                    /* Database connection */

  KeyInfo *pKeyInfo;              /* How to compare records */
  UnpackedRecord *pUnpacked;      /* Space to unpack a record */
  int pgsz;                       /* Main database page size */

  u8 eWork;                       /* One of the SORT_SUBTASK_* constants */
  int nConsolidate;               /* For SORT_SUBTASK_CONS, max final PMAs */
  SorterRecord *pList;            /* List of records for pTask to sort */
  int nInMemory;                  /* Expected size of PMA based on pList */
  u8 *aListMemory;                /* Records memory (or NULL) */


  int nPMA;                       /* Number of PMAs currently in pTemp1 */
  i64 iTemp1Off;                  /* Offset to write to in pTemp1 */
  sqlite3_file *pTemp1;           /* File to write PMAs to, or NULL */


};


/*
** The MergeEngine object is used to combine two or more smaller PMAs into
** one big PMA using a merge operation.  Separate PMAs all need to be
** combined into one big PMA in order to be able to step through the sorted
................................................................................
  int *aTree;                /* Current state of incremental merge */
  PmaReader *aIter;          /* Array of iterators to merge data from */
};

/*
** Main sorter structure. A single instance of this is allocated for each 
** sorter cursor created by the VDBE.





*/
struct VdbeSorter {
  int nInMemory;                  /* Current size of pRecord list as PMA */
  int mnPmaSize;                  /* Minimum PMA size, in bytes */
  int mxPmaSize;                  /* Maximum PMA size, in bytes.  0==no limit */
  int bUsePMA;                    /* True if one or more PMAs created */
  SorterRecord *pRecord;          /* Head of in-memory record list */

  MergeEngine *pMerger;           /* For final merge of PMAs (by caller) */ 
  u8 *aMemory;                    /* Block of memory to alloc records from */



  int iMemory;                    /* Offset of first free byte in aMemory */
  int nMemory;                    /* Size of aMemory allocation in bytes */


  int iPrev;                      /* Previous thread used to flush PMA */
  int nTask;                      /* Size of aTask[] array */
  SortSubtask aTask[1];           /* One or more subtasks */
};

/*
** An instance of the following object is used to read records out of a
** PMA, in sorted order.  The next key to be read is cached in nKey/aKey.
** pFile==0 at EOF.
................................................................................
  int nKey;                       /* Number of bytes in key */
  sqlite3_file *pFile;            /* File iterator is reading from */
  u8 *aAlloc;                     /* Allocated space */
  u8 *aKey;                       /* Pointer to current key */
  u8 *aBuffer;                    /* Current read buffer */
  int nBuffer;                    /* Size of read buffer in bytes */
  u8 *aMap;                       /* Pointer to mapping of entire file */


















};

/*
** An instance of this object is used for writing a PMA.
**
** The PMA is written one record at a time.  Each record is of an arbitrary
** size.  But I/O is more efficient if it occurs in page-sized blocks where
................................................................................
/* The minimum PMA size is set to this value multiplied by the database
** page size in bytes.  */
#define SORTER_MIN_WORKING 10

/* Maximum number of PMAs that a single MergeEngine can merge */
#define SORTER_MAX_MERGE_COUNT 16




/*
** 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);

  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
................................................................................
    ** In this case, allocate space at p->aAlloc[] to copy the requested
    ** range into. Then return a copy of pointer p->aAlloc to the caller.  */
    int nRem;                     /* Bytes remaining to copy */

    /* Extend the p->aAlloc[] allocation if required. */
    if( p->nAlloc<nByte ){
      u8 *aNew;
      int nNew = p->nAlloc*2;
      while( nByte>nNew ) nNew = nNew*2;
      aNew = sqlite3Realloc(p->aAlloc, nNew);
      if( !aNew ) return SQLITE_NOMEM;
      p->nAlloc = nNew;
      p->aAlloc = aNew;
    }

................................................................................
      sqlite3GetVarint(aVarint, pnOut);
    }
  }

  return SQLITE_OK;
}



















































/*
** Advance iterator pIter to the next key in its PMA. Return SQLITE_OK if
** no error occurs, or an SQLite error code if one does.
*/
static int vdbePmaReaderNext(PmaReader *pIter){
  int rc;                         /* Return Code */

  u64 nRec = 0;                   /* Size of record in bytes */

  if( pIter->iReadOff>=pIter->iEof ){










    /* This is an EOF condition */
    vdbePmaReaderClear(pIter);
    return SQLITE_OK;
  }



  rc = vdbePmaReadVarint(pIter, &nRec);

  if( rc==SQLITE_OK ){
    pIter->nKey = (int)nRec;
    rc = vdbePmaReadBlob(pIter, (int)nRec, &pIter->aKey);
  }

  return rc;
}

/*
** Initialize iterator pIter to scan through the PMA stored in file pFile
** starting at offset iStart and ending at offset iEof-1. This function 
** leaves the iterator pointing to the first key in the PMA (or EOF if the 
** PMA is empty).



*/
static int vdbePmaReaderInit(
  SortSubtask *pTask,             /* Thread context */

  i64 iStart,                     /* Start offset in pTask->pTemp1 */
  PmaReader *pIter,               /* Iterator to populate */
  i64 *pnByte                     /* IN/OUT: Increment this value by PMA size */
){
  int rc = SQLITE_OK;
  int nBuf = pTask->pgsz;
  void *pMap = 0;                 /* Mapping of temp file */

  assert( pTask->iTemp1Off>iStart );

  assert( pIter->aAlloc==0 );
  assert( pIter->aBuffer==0 );
  pIter->pFile = pTask->pTemp1;
  pIter->iReadOff = iStart;
  pIter->nAlloc = 128;
  pIter->aAlloc = (u8*)sqlite3Malloc(pIter->nAlloc);
  if( pIter->aAlloc ){
    /* Try to xFetch() a mapping of the entire temp file. If this is possible,
    ** the PMA will be read via the mapping. Otherwise, use xRead().  */
    if( pTask->iTemp1Off<=(i64)(pTask->db->nMaxSorterMmap) ){
      rc = sqlite3OsFetch(pIter->pFile, 0, pTask->iTemp1Off, &pMap);
    }
  }else{
    rc = SQLITE_NOMEM;
  }

  if( rc==SQLITE_OK ){
    if( pMap ){
      pIter->aMap = (u8*)pMap;
    }else{
      pIter->nBuffer = nBuf;
      pIter->aBuffer = (u8*)sqlite3Malloc(nBuf);
      if( !pIter->aBuffer ){
        rc = SQLITE_NOMEM;
      }else{
        int iBuf = iStart % nBuf;
        if( iBuf ){
          int nRead = nBuf - iBuf;
          if( (iStart + nRead) > pTask->iTemp1Off ){
            nRead = (int)(pTask->iTemp1Off - iStart);
          }
          rc = sqlite3OsRead(
              pTask->pTemp1, &pIter->aBuffer[iBuf], nRead, iStart
              );
          assert( rc!=SQLITE_IOERR_SHORT_READ );
        }
      }
    }
  }

  if( rc==SQLITE_OK ){
    u64 nByte;                    /* Size of PMA in bytes */
    pIter->iEof = pTask->iTemp1Off;
    rc = vdbePmaReadVarint(pIter, &nByte);
    pIter->iEof = pIter->iReadOff + nByte;
    *pnByte += nByte;
  }

  if( rc==SQLITE_OK ){
    rc = vdbePmaReaderNext(pIter);
................................................................................
    pKeyInfo = (KeyInfo*)((u8*)pSorter + sz);
    memcpy(pKeyInfo, pCsr->pKeyInfo, szKeyInfo);
    pKeyInfo->db = 0;
    if( nField && nWorker==0 ) pKeyInfo->nField = nField;
    pgsz = sqlite3BtreeGetPageSize(db->aDb[0].pBt);

    pSorter->nTask = nWorker + 1;

    for(i=0; i<pSorter->nTask; i++){
      SortSubtask *pTask = &pSorter->aTask[i];
      pTask->pKeyInfo = pKeyInfo;
      pTask->pgsz = pgsz;
      pTask->db = db;

    }

    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 is using memsys3 or memsys5, use a separate 
      ** allocation for each sort-key in memory. Otherwise, use a single big
      ** allocation at pSorter->aMemory for all sort-keys.  */
      if( sqlite3GlobalConfig.pHeap==0 ){
        assert( pSorter->iMemory==0 );
        pSorter->nMemory = pgsz;
        pSorter->aMemory = (u8*)sqlite3Malloc(pgsz);
        if( !pSorter->aMemory ) rc = SQLITE_NOMEM;
      }
    }
  }

  return rc;
}

................................................................................
/*
** Free all resources owned by the object indicated by argument pTask. All 
** fields of *pTask are zeroed before returning.
*/
static void vdbeSortSubtaskCleanup(sqlite3 *db, SortSubtask *pTask){
  sqlite3DbFree(db, pTask->pUnpacked);
  pTask->pUnpacked = 0;
  if( pTask->aListMemory==0 ){
    vdbeSorterRecordFree(0, pTask->pList);
  }else{
    sqlite3_free(pTask->aListMemory);
    pTask->aListMemory = 0;
  }
  pTask->pList = 0;
  if( pTask->pTemp1 ){
    sqlite3OsCloseFree(pTask->pTemp1);
    pTask->pTemp1 = 0;

  }




}










































/*
** Join all threads.  
*/
#if SQLITE_MAX_WORKER_THREADS>0


































static int vdbeSorterJoinAll(VdbeSorter *pSorter, int rcin){
  int rc = rcin;
  int i;
  for(i=0; i<pSorter->nTask; i++){
    SortSubtask *pTask = &pSorter->aTask[i];
    if( pTask->pThread ){
      void *pRet;
      int rc2 = sqlite3ThreadJoin(pTask->pThread, &pRet);
      pTask->pThread = 0;
      pTask->bDone = 0;

      if( rc==SQLITE_OK ) rc = rc2;
      if( rc==SQLITE_OK ) rc = SQLITE_PTR_TO_INT(pRet);
    }
  }
  return rc;
}
#else
# define vdbeSorterJoinAll(x,rcin) (rcin)

#endif

/*
** Allocate a new MergeEngine object with space for nIter iterators.
*/
static MergeEngine *vdbeMergeEngineNew(int nIter){
  int N = 2;                      /* Smallest power of two >= nIter */
  int nByte;                      /* Total bytes of space to allocate */
  MergeEngine *pNew;              /* Pointer to allocated object to return */

  assert( nIter<=SORTER_MAX_MERGE_COUNT );

  while( N<nIter ) N += N;
  nByte = sizeof(MergeEngine) + N * (sizeof(int) + sizeof(PmaReader));

  pNew = (MergeEngine*)sqlite3MallocZero(nByte);
  if( pNew ){
    pNew->nTree = N;
    pNew->aIter = (PmaReader*)&pNew[1];
................................................................................

/*
** Reset a sorting cursor back to its original empty state.
*/
void sqlite3VdbeSorterReset(sqlite3 *db, VdbeSorter *pSorter){
  int i;
  (void)vdbeSorterJoinAll(pSorter, SQLITE_OK);





  vdbeMergeEngineFree(pSorter->pMerger);
  pSorter->pMerger = 0;
  for(i=0; i<pSorter->nTask; i++){
    SortSubtask *pTask = &pSorter->aTask[i];
    vdbeSortSubtaskCleanup(db, pTask);
  }
  if( pSorter->aMemory==0 ){
    vdbeSorterRecordFree(0, pSorter->pRecord);
  }
  pSorter->pRecord = 0;
  pSorter->nInMemory = 0;
  pSorter->bUsePMA = 0;
  pSorter->iMemory = 0;



}

/*
** Free any cursor components allocated by sqlite3VdbeSorterXXX routines.
*/
void sqlite3VdbeSorterClose(sqlite3 *db, VdbeCursor *pCsr){
  VdbeSorter *pSorter = pCsr->pSorter;
  if( pSorter ){
    sqlite3VdbeSorterReset(db, pSorter);
    vdbeMergeEngineFree(pSorter->pMerger);
    sqlite3_free(pSorter->aMemory);
    sqlite3DbFree(db, pSorter);
    pCsr->pSorter = 0;
  }
}

/*
** Allocate space for a file-handle and open a temporary file. If successful,
................................................................................
  );
  if( rc==SQLITE_OK ){
    i64 max = SQLITE_MAX_MMAP_SIZE;
    sqlite3OsFileControlHint( *ppFile, SQLITE_FCNTL_MMAP_SIZE, (void*)&max);
  }
  return rc;
}
















/*
** Merge the two sorted lists p1 and p2 into a single list.
** Set *ppOut to the head of the new list.
*/
static void vdbeSorterMerge(
  SortSubtask *pTask,             /* Calling thread context */
................................................................................
}

/*
** Sort the linked list of records headed at pTask->pList. Return 
** SQLITE_OK if successful, or an SQLite error code (i.e. SQLITE_NOMEM) if 
** an error occurs.
*/
static int vdbeSorterSort(SortSubtask *pTask){
  int i;
  SorterRecord **aSlot;
  SorterRecord *p;





  aSlot = (SorterRecord **)sqlite3MallocZero(64 * sizeof(SorterRecord *));
  if( !aSlot ){
    return SQLITE_NOMEM;
  }

  p = pTask->pList;
  while( p ){
    SorterRecord *pNext;
    if( pTask->aListMemory ){
      if( (u8*)p==pTask->aListMemory ){
        pNext = 0;
      }else{
        assert( p->u.iNext<sqlite3MallocSize(pTask->aListMemory) );
        pNext = (SorterRecord*)&pTask->aListMemory[p->u.iNext];
      }
    }else{
      pNext = p->u.pNext;
    }

    p->u.pNext = 0;
    for(i=0; aSlot[i]; i++){
................................................................................
    p = pNext;
  }

  p = 0;
  for(i=0; i<64; i++){
    vdbeSorterMerge(pTask, p, aSlot[i], &p);
  }
  pTask->pList = p;

  sqlite3_free(aSlot);




  return SQLITE_OK;
}

/*
** Initialize a PMA-writer object.
*/
static void vdbePmaWriterInit(
................................................................................
}
#else
# define vdbeSorterExtendFile(x,y,z) SQLITE_OK
#endif


/*
** Write the current contents of the in-memory linked-list to a PMA. Return

** SQLITE_OK if successful, or an SQLite error code otherwise.
**
** The format of a PMA is:
**
**     * A varint. This varint contains the total number of bytes of content
**       in the PMA (not including the varint itself).
**
**     * One or more records packed end-to-end in order of ascending keys. 
**       Each record consists of a varint followed by a blob of data (the 
**       key). The varint is the number of bytes in the blob of data.
*/
static int vdbeSorterListToPMA(SortSubtask *pTask){
  int rc = SQLITE_OK;             /* Return code */
  PmaWriter writer;               /* Object used to write to the file */








  memset(&writer, 0, sizeof(PmaWriter));
  assert( pTask->nInMemory>0 );


  /* If the first temporary PMA file has not been opened, open it now. */
  if( pTask->pTemp1==0 ){
    rc = vdbeSorterOpenTempFile(pTask->db->pVfs, &pTask->pTemp1);
    assert( rc!=SQLITE_OK || pTask->pTemp1 );
    assert( pTask->iTemp1Off==0 );
    assert( pTask->nPMA==0 );
  }

  /* Try to get the file to memory map */
  if( rc==SQLITE_OK ){
    vdbeSorterExtendFile(pTask->db, 
        pTask->pTemp1, pTask->iTemp1Off + pTask->nInMemory + 9
    );
  }






  if( rc==SQLITE_OK ){
    SorterRecord *p;
    SorterRecord *pNext = 0;

    vdbePmaWriterInit(pTask->pTemp1, &writer, pTask->pgsz,
                      pTask->iTemp1Off);
    pTask->nPMA++;
    vdbePmaWriteVarint(&writer, pTask->nInMemory);
    for(p=pTask->pList; p; p=pNext){
      pNext = p->u.pNext;
      vdbePmaWriteVarint(&writer, p->nVal);
      vdbePmaWriteBlob(&writer, SRVAL(p), p->nVal);
      if( pTask->aListMemory==0 ) sqlite3_free(p);
    }
    pTask->pList = p;
    rc = vdbePmaWriterFinish(&writer, &pTask->iTemp1Off);
  }

  assert( pTask->pList==0 || rc!=SQLITE_OK );


  return rc;
}

/*
** Advance the MergeEngine iterator passed as the second argument to
** the next entry. Set *pbEof to true if this means the iterator has 
** reached EOF.
................................................................................

  return rc;
}

/*
** The main routine for sorter-thread operations.
*/
static void *vdbeSortSubtaskMain(void *pCtx){
  int rc = SQLITE_OK;
  SortSubtask *pTask = (SortSubtask*)pCtx;

  assert( pTask->eWork==SORT_SUBTASK_SORT
       || pTask->eWork==SORT_SUBTASK_TO_PMA
       || pTask->eWork==SORT_SUBTASK_CONS
  );

  assert( pTask->bDone==0 );

  if( pTask->pUnpacked==0 ){
    char *pFree;
    pTask->pUnpacked = sqlite3VdbeAllocUnpackedRecord(
        pTask->pKeyInfo, 0, 0, &pFree
    );
    assert( pTask->pUnpacked==(UnpackedRecord*)pFree );
    if( pFree==0 ){
      rc = SQLITE_NOMEM;
      goto thread_out;
    }
    pTask->pUnpacked->nField = pTask->pKeyInfo->nField;
    pTask->pUnpacked->errCode = 0;
  }

  if( pTask->eWork==SORT_SUBTASK_CONS ){
    assert( pTask->pList==0 );
    while( pTask->nPMA>pTask->nConsolidate && rc==SQLITE_OK ){
      int nIter = MIN(pTask->nPMA, SORTER_MAX_MERGE_COUNT);
      sqlite3_file *pTemp2 = 0;     /* Second temp file to use */
      MergeEngine *pMerger;         /* Object for reading/merging PMA data */
      i64 iReadOff = 0;             /* Offset in pTemp1 to read from */
      i64 iWriteOff = 0;            /* Offset in pTemp2 to write to */
      int i;
      
      /* Allocate a merger object to merge PMAs together. */
      pMerger = vdbeMergeEngineNew(nIter);
      if( pMerger==0 ){
        rc = SQLITE_NOMEM;
        break;
      }

      /* Open a second temp file to write merged data to */
      rc = vdbeSorterOpenTempFile(pTask->db->pVfs, &pTemp2);
      if( rc==SQLITE_OK ){
        vdbeSorterExtendFile(pTask->db, pTemp2, pTask->iTemp1Off);
      }else{
        vdbeMergeEngineFree(pMerger);
        break;
      }

      /* This loop runs once for each output PMA. Each output PMA is made
      ** of data merged from up to SORTER_MAX_MERGE_COUNT input PMAs. */
      for(i=0; rc==SQLITE_OK && i<pTask->nPMA; i+=SORTER_MAX_MERGE_COUNT){
        PmaWriter writer;         /* Object for writing data to pTemp2 */
        i64 nOut = 0;             /* Bytes of data in output PMA */
        int bEof = 0;
        int rc2;

        /* Configure the merger object to read and merge data from the next 
        ** SORTER_MAX_MERGE_COUNT PMAs in pTemp1 (or from all remaining PMAs,
        ** if that is fewer). */
        int iIter;
        for(iIter=0; iIter<SORTER_MAX_MERGE_COUNT; iIter++){
          PmaReader *pIter = &pMerger->aIter[iIter];
          rc = vdbePmaReaderInit(pTask, iReadOff, pIter, &nOut);
          iReadOff = pIter->iEof;
          if( iReadOff>=pTask->iTemp1Off || rc!=SQLITE_OK ) break;
        }
        for(iIter=pMerger->nTree-1; rc==SQLITE_OK && iIter>0; iIter--){
          rc = vdbeSorterDoCompare(pTask, pMerger, iIter);
        }

        vdbePmaWriterInit(pTemp2, &writer, pTask->pgsz, iWriteOff);
        vdbePmaWriteVarint(&writer, nOut);
        while( rc==SQLITE_OK && bEof==0 ){
          PmaReader *pIter = &pMerger->aIter[ pMerger->aTree[1] ];
          assert( pIter->pFile!=0 );        /* pIter is not at EOF */
          vdbePmaWriteVarint(&writer, pIter->nKey);
          vdbePmaWriteBlob(&writer, pIter->aKey, pIter->nKey);
          rc = vdbeSorterNext(pTask, pMerger, &bEof);
        }
        rc2 = vdbePmaWriterFinish(&writer, &iWriteOff);
        if( rc==SQLITE_OK ) rc = rc2;
      }

      vdbeMergeEngineFree(pMerger);
      sqlite3OsCloseFree(pTask->pTemp1);
      pTask->pTemp1 = pTemp2;
      pTask->nPMA = (i / SORTER_MAX_MERGE_COUNT);
      pTask->iTemp1Off = iWriteOff;
    }
  }else{
    /* Sort the pTask->pList list */
    rc = vdbeSorterSort(pTask);

    /* If required, write the list out to a PMA. */
    if( rc==SQLITE_OK && pTask->eWork==SORT_SUBTASK_TO_PMA ){
#ifdef SQLITE_DEBUG
      i64 nExpect = pTask->nInMemory
        + sqlite3VarintLen(pTask->nInMemory)
        + pTask->iTemp1Off;
#endif
      rc = vdbeSorterListToPMA(pTask);
      assert( rc!=SQLITE_OK || (nExpect==pTask->iTemp1Off) );
    }
  }

 thread_out:
  pTask->bDone = 1;
  if( rc==SQLITE_OK && pTask->pUnpacked->errCode ){
    assert( pTask->pUnpacked->errCode==SQLITE_NOMEM );
    rc = SQLITE_NOMEM;
  }
  return SQLITE_INT_TO_PTR(rc);
}

/*
** Run the activity scheduled by the object passed as the only argument
** in the current thread.
*/
static int vdbeSorterRunTask(SortSubtask *pTask){
  int rc = SQLITE_PTR_TO_INT( vdbeSortSubtaskMain((void*)pTask) );
  assert( pTask->bDone );
  pTask->bDone = 0;
  return rc;
}

/*
** Flush the current contents of VdbeSorter.pRecord to a new PMA, possibly
** using a background thread.
**
** If argument bFg is non-zero, the operation always uses the calling thread.
*/
static int vdbeSorterFlushPMA(sqlite3 *db, const VdbeCursor *pCsr, int bFg){
  VdbeSorter *pSorter = pCsr->pSorter;




  int rc = SQLITE_OK;
  int i;
  SortSubtask *pTask = 0;    /* Thread context used to create new PMA */
  int nWorker = (pSorter->nTask-1);



  pSorter->bUsePMA = 1;









  for(i=0; i<nWorker; i++){
    int iTest = (pSorter->iPrev + i + 1) % nWorker;
    pTask = &pSorter->aTask[iTest];
#if SQLITE_MAX_WORKER_THREADS>0
    if( pTask->bDone ){
      void *pRet;


      assert( pTask->pThread );
      rc = sqlite3ThreadJoin(pTask->pThread, &pRet);
      pTask->pThread = 0;
      pTask->bDone = 0;
      if( rc==SQLITE_OK ){
        rc = SQLITE_PTR_TO_INT(pRet);
      }
    }





#endif
    if( pTask->pThread==0 ) break;
    pTask = 0;
  }
  if( pTask==0 ){
    pTask = &pSorter->aTask[nWorker];

  }
  pSorter->iPrev = (pTask - pSorter->aTask);

  if( rc==SQLITE_OK ){
    assert( pTask->pThread==0 && pTask->bDone==0 );
    pTask->eWork = SORT_SUBTASK_TO_PMA;
    pTask->pList = pSorter->pRecord;
    pTask->nInMemory = pSorter->nInMemory;
    pSorter->nInMemory = 0;
    pSorter->pRecord = 0;

    if( pSorter->aMemory ){
      u8 *aMem = pTask->aListMemory;
      pTask->aListMemory = pSorter->aMemory;

      pSorter->aMemory = aMem;
    }

#if SQLITE_MAX_WORKER_THREADS>0
    if( !bFg && pTask!=&pSorter->aTask[nWorker] ){
      /* Launch a background thread for this operation */
      void *pCtx = (void*)pTask;
      assert( pSorter->aMemory==0 || pTask->aListMemory!=0 );
      if( pTask->aListMemory ){
        if( pSorter->aMemory==0 ){
          pSorter->aMemory = sqlite3Malloc(pSorter->nMemory);
          if( pSorter->aMemory==0 ) return SQLITE_NOMEM;
        }else{
          pSorter->nMemory = sqlite3MallocSize(pSorter->aMemory);

        }
      }
      rc = sqlite3ThreadCreate(&pTask->pThread, vdbeSortSubtaskMain, pCtx);
    }else
#endif
    {
      /* Use the foreground thread for this operation */
      rc = vdbeSorterRunTask(pTask);
      if( rc==SQLITE_OK ){
        u8 *aMem = pTask->aListMemory;
        pTask->aListMemory = pSorter->aMemory;
        pSorter->aMemory = aMem;
        assert( pTask->pList==0 );
      }

    }
  }

  return rc;

}

/*
** Add a record to the sorter.
*/
int sqlite3VdbeSorterWrite(
  sqlite3 *db,                    /* Database handle */
................................................................................
  **
  **   * The total memory allocated for the in-memory list is greater 
  **     than (page-size * 10) and sqlite3HeapNearlyFull() returns true.
  */
  nReq = pVal->n + sizeof(SorterRecord);
  nPMA = pVal->n + sqlite3VarintLen(pVal->n);
  if( pSorter->mxPmaSize ){
    if( pSorter->aMemory ){
      bFlush = pSorter->iMemory && (pSorter->iMemory+nReq) > pSorter->mxPmaSize;
    }else{
      bFlush = (
          (pSorter->nInMemory > pSorter->mxPmaSize)
       || (pSorter->nInMemory > pSorter->mnPmaSize && sqlite3HeapNearlyFull())
      );
    }
    if( bFlush ){
      rc = vdbeSorterFlushPMA(db, pCsr, 0);
      pSorter->nInMemory = 0;
      pSorter->iMemory = 0;
      assert( rc!=SQLITE_OK || pSorter->pRecord==0 );
    }
  }

  pSorter->nInMemory += nPMA;




  if( pSorter->aMemory ){
    int nMin = pSorter->iMemory + nReq;

    if( nMin>pSorter->nMemory ){
      u8 *aNew;
      int nNew = pSorter->nMemory * 2;
      while( nNew < nMin ) nNew = nNew*2;
      if( nNew > pSorter->mxPmaSize ) nNew = pSorter->mxPmaSize;
      if( nNew < nMin ) nNew = nMin;

      aNew = sqlite3Realloc(pSorter->aMemory, nNew);
      if( !aNew ) return SQLITE_NOMEM;
      pSorter->pRecord = (SorterRecord*)(
          aNew + ((u8*)pSorter->pRecord - pSorter->aMemory)
      );
      pSorter->aMemory = aNew;
      pSorter->nMemory = nNew;
    }

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

  memcpy(SRVAL(pNew), pVal->z, pVal->n);
  pNew->nVal = pVal->n;
  pSorter->pRecord = pNew;

  return rc;
}

/*
** Return the total number of PMAs in all temporary files.


*/


























































































































static int vdbeSorterCountPMA(VdbeSorter *pSorter){




  int nPMA = 0;


































































































  int i;











































































  for(i=0; i<pSorter->nTask; i++){


















































































    nPMA += pSorter->aTask[i].nPMA;




  }
















  return nPMA;
}


/*
** 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(sqlite3 *db, const VdbeCursor *pCsr, int *pbEof){
................................................................................

  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->bUsePMA==0 ){
    if( pSorter->pRecord ){
      SortSubtask *pTask = &pSorter->aTask[0];
      *pbEof = 0;
      pTask->pList = pSorter->pRecord;
      pTask->eWork = SORT_SUBTASK_SORT;
      assert( pTask->aListMemory==0 );
      pTask->aListMemory = pSorter->aMemory;
      rc = vdbeSorterRunTask(pTask);
      pTask->aListMemory = 0;
      pSorter->pRecord = pTask->pList;
      pTask->pList = 0;

    }else{
      *pbEof = 1;
    }
    return rc;
  }

  /* Write the current in-memory list to a PMA. */
  if( pSorter->pRecord ){
    rc = vdbeSorterFlushPMA(db, pCsr, 1);
  }

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

  /* If there are more than SORTER_MAX_MERGE_COUNT PMAs on disk, merge
  ** some of them together so that this is no longer the case. */
  if( vdbeSorterCountPMA(pSorter)>SORTER_MAX_MERGE_COUNT ){
    int i;
    for(i=0; rc==SQLITE_OK && i<pSorter->nTask; i++){
      SortSubtask *pTask = &pSorter->aTask[i];
      if( pTask->pTemp1 ){
        pTask->nConsolidate = SORTER_MAX_MERGE_COUNT / pSorter->nTask;
        pTask->eWork = SORT_SUBTASK_CONS;

#if SQLITE_MAX_WORKER_THREADS>0
        if( i<(pSorter->nTask-1) ){
          void *pCtx = (void*)pTask;
          rc = sqlite3ThreadCreate(&pTask->pThread, vdbeSortSubtaskMain, pCtx);
        }else
#endif
        {
          rc = vdbeSorterRunTask(pTask);
        }
      }
    }
  }

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

  /* Assuming no errors have occurred, set up a merger structure to read
  ** and merge all remaining PMAs.  */
  assert( pSorter->pMerger==0 );
  if( rc==SQLITE_OK ){
    int nIter = 0;                /* Number of iterators used */
    int i;
    MergeEngine *pMerger;
    for(i=0; i<pSorter->nTask; i++){
      nIter += pSorter->aTask[i].nPMA;
    }

    pSorter->pMerger = pMerger = vdbeMergeEngineNew(nIter);
    if( pMerger==0 ){
      rc = SQLITE_NOMEM;
    }else{
      int iIter = 0;
      int iThread = 0;
      for(iThread=0; iThread<pSorter->nTask; iThread++){
        int iPMA;
        i64 iReadOff = 0;
        SortSubtask *pTask = &pSorter->aTask[iThread];
        for(iPMA=0; iPMA<pTask->nPMA && rc==SQLITE_OK; iPMA++){
          i64 nDummy = 0;
          PmaReader *pIter = &pMerger->aIter[iIter++];
          rc = vdbePmaReaderInit(pTask, iReadOff, pIter, &nDummy);
          iReadOff = pIter->iEof;

        }
      }

      for(i=pMerger->nTree-1; rc==SQLITE_OK && i>0; i--){
        rc = vdbeSorterDoCompare(&pSorter->aTask[0], pMerger, i);
      }
    }
  }

  if( rc==SQLITE_OK ){
    *pbEof = (pSorter->pMerger->aIter[pSorter->pMerger->aTree[1]].pFile==0);
  }

  return rc;
}

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


  if( pSorter->pMerger ){







    rc = vdbeSorterNext(&pSorter->aTask[0], pSorter->pMerger, pbEof);

  }else{
    SorterRecord *pFree = pSorter->pRecord;
    pSorter->pRecord = pFree->u.pNext;
    pFree->u.pNext = 0;
    if( pSorter->aMemory==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(
  const VdbeSorter *pSorter,      /* Sorter object */
  int *pnKey                      /* OUT: Size of current key in bytes */
){
  void *pKey;
  if( pSorter->pMerger ){
    PmaReader *pIter;
    pIter = &pSorter->pMerger->aIter[ pSorter->pMerger->aTree[1] ];

    *pnKey = pIter->nKey;
    pKey = pIter->aKey;
  }else{
    *pnKey = pSorter->pRecord->nVal;
    pKey = SRVAL(pSorter->pRecord);
  }
  return pKey;
}

/*
** Copy the current sorter key into the memory cell pOut.
*/
................................................................................
int sqlite3VdbeSorterCompare(
  const VdbeCursor *pCsr,         /* Sorter cursor */
  Mem *pVal,                      /* Value to compare to current sorter key */
  int nIgnore,                    /* Ignore this many fields at the end */
  int *pRes                       /* OUT: Result of comparison */
){
  VdbeSorter *pSorter = pCsr->pSorter;
  UnpackedRecord *r2 = pSorter->aTask[0].pUnpacked;
  KeyInfo *pKeyInfo = pCsr->pKeyInfo;
  int i;
  void *pKey; int nKey;           /* Sorter key to compare pVal with */






  assert( r2->nField>=pKeyInfo->nField-nIgnore );

  r2->nField = pKeyInfo->nField-nIgnore;

  pKey = vdbeSorterRowkey(pSorter, &nKey);
  sqlite3VdbeRecordUnpack(pKeyInfo, nKey, pKey, r2);
  for(i=0; i<r2->nField; i++){
    if( r2->aMem[i].flags & MEM_Null ){
      *pRes = -1;
      return SQLITE_OK;
    }
  }

  *pRes = sqlite3VdbeRecordCompare(pVal->n, pVal->z, r2, 0);
  return SQLITE_OK;
}







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** algorithm might be performed in parallel by separate threads.  Threads
** are only used when one or more PMA spill to disk.  If the sort is small
** enough to fit entirely in memory, everything happens on the main thread.
*/
#include "sqliteInt.h"
#include "vdbeInt.h"

/* 
** If SQLITE_DEBUG_SORTER_THREADS is defined, this module outputs various
** messages to stderr that may be helpful in understanding the performance
** characteristics of the sorter in multi-threaded mode.
*/
#if 0
# define SQLITE_DEBUG_SORTER_THREADS 1
#endif

/*
** Private objects used by the sorter
*/
typedef struct MergeEngine MergeEngine;     /* Merge PMAs together */
typedef struct PmaReader PmaReader;         /* Incrementally read one PMA */
typedef struct PmaWriter PmaWriter;         /* Incrementally write on PMA */
typedef struct SorterRecord SorterRecord;   /* A record being sorted */
typedef struct SortSubtask SortSubtask;     /* A sub-task in the sort process */
typedef struct SorterFile SorterFile;
typedef struct SorterThread SorterThread;
typedef struct SorterList SorterList;
typedef struct IncrMerger IncrMerger;

/*
** A container for a temp file handle and the current amount of data 
** stored in the file.
*/
struct SorterFile {
  sqlite3_file *pFd;              /* File handle */
  i64 iEof;                       /* Bytes of data stored in pFd */
};

/*

** An object of this type is used to store the thread handle for each 
** background thread launched by the sorter. Before the thread is launched,
** variable bDone is set to 0. Then, right before it exits, the thread 
** itself sets bDone to 1.
**
** This is then used for two purposes:
**
**   1. When flushing the contents of memory to a level-0 PMA on disk, to
**      attempt to select a SortSubtask for which there is not already an
**      active background thread (since doing so causes the main thread
**      to block until it finishes).
**
**   2. If SQLITE_DEBUG_SORTER_THREADS is defined, to determine if a call
**      to sqlite3ThreadJoin() is likely to block.
**
** In both cases, the effects of the main thread seeing (bDone==0) even
** after the thread has finished are not dire. So we don't worry about
** memory barriers and such here.
*/



struct SorterThread {
  SQLiteThread *pThread;
  int bDone;
};

struct SorterList {
  SorterRecord *pList;            /* Linked list of records */
  u8 *aMemory;                    /* If non-NULL, blob of memory for pList */
  int szPMA;                      /* Size of pList as PMA in bytes */
};

/*
** Sorting is divided up into smaller subtasks.  Each subtask is controlled
** by an instance of this object. A Subtask might run in either the main thread
** or in a background thread.
**
** Exactly VdbeSorter.nTask instances of this object are allocated
................................................................................
**     the temp file if it is not already open.
**
**   SORT_SUBTASK_CONS:
**     Merge existing PMAs until SortSubtask.nConsolidate or fewer
**     remain in temp file SortSubtask.pTemp1.
*/
struct SortSubtask {
  SorterThread thread;


  sqlite3 *db;                    /* Database connection */
  VdbeSorter *pSorter;            /* Sorter */
  KeyInfo *pKeyInfo;              /* How to compare records */
  UnpackedRecord *pUnpacked;      /* Space to unpack a record */
  int pgsz;                       /* Main database page size */







  SorterList list;                /* List for thread to write to a PMA */
  int nPMA;                       /* Number of PMAs currently in file */


  SorterFile file;                /* Temp file for level-0 PMAs */
  SorterFile file2;               /* Space for other PMAs */
};


/*
** The MergeEngine object is used to combine two or more smaller PMAs into
** one big PMA using a merge operation.  Separate PMAs all need to be
** combined into one big PMA in order to be able to step through the sorted
................................................................................
  int *aTree;                /* Current state of incremental merge */
  PmaReader *aIter;          /* Array of iterators to merge data from */
};

/*
** Main sorter structure. A single instance of this is allocated for each 
** sorter cursor created by the VDBE.
**
** mxKeysize:
**   As records are added to the sorter by calls to sqlite3VdbeSorterWrite(),
**   this variable is updated so as to be set to the size on disk of the
**   largest record in the sorter.
*/
struct VdbeSorter {

  int mnPmaSize;                  /* Minimum PMA size, in bytes */
  int mxPmaSize;                  /* Maximum PMA size, in bytes.  0==no limit */


  PmaReader *pReader;             /* Read data from here after Rewind() */
  MergeEngine *pMerger;           /* Or here, if bUseThreads==0 */

  int mxKeysize;                  /* Largest serialized key seen so far */
  UnpackedRecord *pUnpacked;      /* Used by VdbeSorterCompare() */
  SorterList list;                /* List of in-memory records */
  int iMemory;                    /* Offset of free space in list.aMemory */
  int nMemory;                    /* Size of list.aMemory allocation in bytes */
  u8 bUsePMA;                     /* True if one or more PMAs created */
  u8 bUseThreads;                 /* True to use background threads */
  u8 iPrev;                       /* Previous thread used to flush PMA */
  u8 nTask;                       /* Size of aTask[] array */
  SortSubtask aTask[1];           /* One or more subtasks */
};

/*
** An instance of the following object is used to read records out of a
** PMA, in sorted order.  The next key to be read is cached in nKey/aKey.
** pFile==0 at EOF.
................................................................................
  int nKey;                       /* Number of bytes in key */
  sqlite3_file *pFile;            /* File iterator is reading from */
  u8 *aAlloc;                     /* Allocated space */
  u8 *aKey;                       /* Pointer to current key */
  u8 *aBuffer;                    /* Current read buffer */
  int nBuffer;                    /* Size of read buffer in bytes */
  u8 *aMap;                       /* Pointer to mapping of entire file */
  IncrMerger *pIncr;              /* Incremental merger */
};

/*
** Normally, a PmaReader object iterates through an existing PMA stored 
** within a temp file. However, if the PmaReader.pIncr variable points to
** an object of the following type, it may be used to iterate/merge through
** multiple PMAs simultaneously.
*/
struct IncrMerger {
  SortSubtask *pTask;             /* Task that owns this merger */
  SorterThread thread;            /* Thread for populating aFile[1] */
  MergeEngine *pMerger;           /* Merge engine thread reads data from */
  i64 iStartOff;                  /* Offset to start writing file at */
  int mxSz;                       /* Maximum bytes of data to store */
  int bEof;                       /* Set to true when merge is finished */
  int bUseThread;                 /* True to use a bg thread for this object */
  SorterFile aFile[2];            /* aFile[0] for reading, [1] for writing */
};

/*
** An instance of this object is used for writing a PMA.
**
** The PMA is written one record at a time.  Each record is of an arbitrary
** size.  But I/O is more efficient if it occurs in page-sized blocks where
................................................................................
/* The minimum PMA size is set to this value multiplied by the database
** page size in bytes.  */
#define SORTER_MIN_WORKING 10

/* Maximum number of PMAs that a single MergeEngine can merge */
#define SORTER_MAX_MERGE_COUNT 16

static int vdbeIncrSwap(IncrMerger*);
static void vdbeIncrFree(IncrMerger*);

/*
** 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);
  if( pIter->pIncr ) 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
................................................................................
    ** In this case, allocate space at p->aAlloc[] to copy the requested
    ** range into. Then return a copy of pointer p->aAlloc to the caller.  */
    int nRem;                     /* Bytes remaining to copy */

    /* Extend the p->aAlloc[] allocation if required. */
    if( p->nAlloc<nByte ){
      u8 *aNew;
      int nNew = MAX(128, p->nAlloc*2);
      while( nByte>nNew ) nNew = nNew*2;
      aNew = sqlite3Realloc(p->aAlloc, nNew);
      if( !aNew ) return SQLITE_NOMEM;
      p->nAlloc = nNew;
      p->aAlloc = aNew;
    }

................................................................................
      sqlite3GetVarint(aVarint, pnOut);
    }
  }

  return SQLITE_OK;
}

static int vdbeSorterMapFile(SortSubtask *pTask, SorterFile *pFile, u8 **pp){
  int rc = SQLITE_OK;
  if( pFile->iEof<=(i64)(pTask->db->nMaxSorterMmap) ){
    rc = sqlite3OsFetch(pFile->pFd, 0, pFile->iEof, (void**)pp);
  }
  return rc;
}

static int vdbePmaReaderReinit(PmaReader *pIter){
  IncrMerger *pIncr = pIter->pIncr;
  SortSubtask *pTask = pIncr->pTask;
  int rc = SQLITE_OK;

  assert( pIncr->bEof==0 );

  if( pIter->aMap ){
    sqlite3OsUnfetch(pIter->pFile, 0, pIter->aMap);
    pIter->aMap = 0;
  }
  pIter->iReadOff = pIncr->iStartOff;
  pIter->iEof = pIncr->aFile[0].iEof;
  pIter->pFile = pIncr->aFile[0].pFd;

  rc = vdbeSorterMapFile(pTask, &pIncr->aFile[0], &pIter->aMap);
  if( rc==SQLITE_OK ){
    if( pIter->aMap==0 ){
      /* TODO: Combine this code with similar code in vdbePmaReaderInit() */
      int iBuf = pIter->iReadOff % pTask->pgsz;
      if( pIter->aBuffer==0 ){
        pIter->aBuffer = (u8*)sqlite3Malloc(pTask->pgsz);
        if( pIter->aBuffer==0 ) rc = SQLITE_NOMEM;
        pIter->nBuffer = pTask->pgsz;
      }
      if( iBuf ){
        int nRead = pTask->pgsz - iBuf;
        if( (pIter->iReadOff + nRead) > pIter->iEof ){
          nRead = (int)(pIter->iEof - pIter->iReadOff);
        }
        rc = sqlite3OsRead(
            pIter->pFile, &pIter->aBuffer[iBuf], nRead, pIter->iReadOff
        );
        assert( rc!=SQLITE_IOERR_SHORT_READ );
      }
    }
  }

  return rc;
}


/*
** Advance iterator pIter to the next key in its PMA. Return SQLITE_OK if
** no error occurs, or an SQLite error code if one does.
*/
static int vdbePmaReaderNext(PmaReader *pIter){

  int rc = SQLITE_OK;             /* Return Code */
  u64 nRec = 0;                   /* Size of record in bytes */

  if( pIter->iReadOff>=pIter->iEof ){
    int bEof = 1;
    if( pIter->pIncr ){
      rc = vdbeIncrSwap(pIter->pIncr);
      if( rc==SQLITE_OK && pIter->pIncr->bEof==0 ){
        rc = vdbePmaReaderReinit(pIter);
        bEof = 0;
      }
    }

    if( bEof ){
      /* This is an EOF condition */
      vdbePmaReaderClear(pIter);
      return rc;
    }
  }

  if( rc==SQLITE_OK ){
    rc = vdbePmaReadVarint(pIter, &nRec);
  }
  if( rc==SQLITE_OK ){
    pIter->nKey = (int)nRec;
    rc = vdbePmaReadBlob(pIter, (int)nRec, &pIter->aKey);
  }

  return rc;
}

/*
** Initialize iterator pIter to scan through the PMA stored in file pFile
** starting at offset iStart and ending at offset iEof-1. This function 
** leaves the iterator pointing to the first key in the PMA (or EOF if the 
** PMA is empty).
**
** If the pnByte parameter is NULL, then it is assumed that the file 
** contains a single PMA, and that that PMA omits the initial length varint.
*/
static int vdbePmaReaderInit(
  SortSubtask *pTask,             /* Task context */
  SorterFile *pFile,              /* Sorter file to read from */
  i64 iStart,                     /* Start offset in pFile */
  PmaReader *pIter,               /* Iterator to populate */
  i64 *pnByte                     /* IN/OUT: Increment this value by PMA size */
){
  int rc = SQLITE_OK;
  int nBuf = pTask->pgsz;



  assert( pFile->iEof>iStart );
  assert( pIter->aAlloc==0 );
  assert( pIter->aBuffer==0 );
  pIter->pFile = pFile->pFd;
  pIter->iReadOff = iStart;
  pIter->nAlloc = 128;
  pIter->aAlloc = (u8*)sqlite3Malloc(pIter->nAlloc);
  if( pIter->aAlloc ){
    /* Try to xFetch() a mapping of the entire temp file. If this is possible,
    ** the PMA will be read via the mapping. Otherwise, use xRead().  */
    rc = vdbeSorterMapFile(pTask, pFile, &pIter->aMap);


  }else{
    rc = SQLITE_NOMEM;
  }

  if( rc==SQLITE_OK && pIter->aMap==0 ){



    pIter->nBuffer = nBuf;
    pIter->aBuffer = (u8*)sqlite3Malloc(nBuf);
    if( !pIter->aBuffer ){
      rc = SQLITE_NOMEM;
    }else{
      int iBuf = iStart % nBuf;
      if( iBuf ){
        int nRead = nBuf - iBuf;
        if( (iStart + nRead) > pFile->iEof ){
          nRead = (int)(pFile->iEof - iStart);
        }
        rc = sqlite3OsRead(
            pIter->pFile, &pIter->aBuffer[iBuf], nRead, iStart
        );
        assert( rc!=SQLITE_IOERR_SHORT_READ );

      }
    }
  }

  if( rc==SQLITE_OK ){
    u64 nByte;                    /* Size of PMA in bytes */
    pIter->iEof = pFile->iEof;
    rc = vdbePmaReadVarint(pIter, &nByte);
    pIter->iEof = pIter->iReadOff + nByte;
    *pnByte += nByte;
  }

  if( rc==SQLITE_OK ){
    rc = vdbePmaReaderNext(pIter);
................................................................................
    pKeyInfo = (KeyInfo*)((u8*)pSorter + sz);
    memcpy(pKeyInfo, pCsr->pKeyInfo, szKeyInfo);
    pKeyInfo->db = 0;
    if( nField && nWorker==0 ) pKeyInfo->nField = nField;
    pgsz = sqlite3BtreeGetPageSize(db->aDb[0].pBt);

    pSorter->nTask = nWorker + 1;
    pSorter->bUseThreads = (pSorter->nTask>1);
    for(i=0; i<pSorter->nTask; i++){
      SortSubtask *pTask = &pSorter->aTask[i];
      pTask->pKeyInfo = pKeyInfo;
      pTask->pgsz = pgsz;
      pTask->db = db;
      pTask->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 is using memsys3 or memsys5, use a separate 
      ** allocation for each sort-key in memory. Otherwise, use a single big
      ** allocation at pSorter->aMemory for all sort-keys.  */
      if( sqlite3GlobalConfig.pHeap==0 ){
        assert( pSorter->iMemory==0 );
        pSorter->nMemory = pgsz;
        pSorter->list.aMemory = (u8*)sqlite3Malloc(pgsz);
        if( !pSorter->list.aMemory ) rc = SQLITE_NOMEM;
      }
    }
  }

  return rc;
}

................................................................................
/*
** Free all resources owned by the object indicated by argument pTask. All 
** fields of *pTask are zeroed before returning.
*/
static void vdbeSortSubtaskCleanup(sqlite3 *db, SortSubtask *pTask){
  sqlite3DbFree(db, pTask->pUnpacked);
  pTask->pUnpacked = 0;
  if( pTask->list.aMemory==0 ){
    vdbeSorterRecordFree(0, pTask->list.pList);
  }else{
    sqlite3_free(pTask->list.aMemory);
    pTask->list.aMemory = 0;
  }
  pTask->list.pList = 0;
  if( pTask->file.pFd ){
    sqlite3OsCloseFree(pTask->file.pFd);
    pTask->file.pFd = 0;
    pTask->file.iEof = 0;
  }
  if( pTask->file2.pFd ){
    sqlite3OsCloseFree(pTask->file2.pFd);
    pTask->file2.pFd = 0;
    pTask->file2.iEof = 0;
  }
}

#ifdef SQLITE_DEBUG_SORTER_THREADS
static void vdbeSorterWorkDebug(SortSubtask *pTask, const char *zEvent){
  i64 t;
  int iTask = (pTask - pTask->pSorter->aTask);
  sqlite3OsCurrentTimeInt64(pTask->db->pVfs, &t);
  fprintf(stderr, "%lld:%d %s\n", t, iTask, zEvent);
}
static void vdbeSorterRewindDebug(sqlite3 *db, const char *zEvent){
  i64 t;
  sqlite3OsCurrentTimeInt64(db->pVfs, &t);
  fprintf(stderr, "%lld:X %s\n", t, zEvent);
}
static void vdbeSorterPopulateDebug(
  SortSubtask *pTask,
  const char *zEvent
){
  i64 t;
  int iTask = (pTask - pTask->pSorter->aTask);
  sqlite3OsCurrentTimeInt64(pTask->db->pVfs, &t);
  fprintf(stderr, "%lld:bg%d %s\n", t, iTask, zEvent);
}
static void vdbeSorterBlockDebug(
  SortSubtask *pTask,
  int bBlocked,
  const char *zEvent
){
  if( bBlocked ){
    i64 t;
    sqlite3OsCurrentTimeInt64(pTask->db->pVfs, &t);
    fprintf(stderr, "%lld:main %s\n", t, zEvent);
  }
}
#else
# define vdbeSorterWorkDebug(x,y)
# define vdbeSorterRewindDebug(x,y)
# define vdbeSorterPopulateDebug(x,y)
# define vdbeSorterBlockDebug(x,y,z)
#endif

#if SQLITE_MAX_WORKER_THREADS>0
/*
** Join thread p.
*/

static int vdbeSorterJoinThread(SortSubtask *pTask, SorterThread *p){
  int rc = SQLITE_OK;
  if( p->pThread ){
#ifdef SQLITE_DEBUG_SORTER_THREADS
    int bDone = p->bDone;
#endif
    void *pRet;
    vdbeSorterBlockDebug(pTask, !bDone, "enter");
    rc = sqlite3ThreadJoin(p->pThread, &pRet);
    vdbeSorterBlockDebug(pTask, !bDone, "exit");
    if( rc==SQLITE_OK ) rc = SQLITE_PTR_TO_INT(pRet);
    assert( p->bDone==1 );
    p->bDone = 0;
    p->pThread = 0;
  }
  return rc;
}

/*
** Launch a background thread to run xTask(pIn).
*/
static int vdbeSorterCreateThread(
  SorterThread *p,                /* Thread object to populate */
  void *(*xTask)(void*),          /* Routine to run in a separate thread */
  void *pIn                       /* Argument passed into xTask() */
){
  assert( p->pThread==0 && p->bDone==0 );
  return sqlite3ThreadCreate(&p->pThread, xTask, pIn);
}

/*
** Join all outstanding threads launched by SorterWrite() to create 
** level-0 PMAs.
*/
static int vdbeSorterJoinAll(VdbeSorter *pSorter, int rcin){
  int rc = rcin;
  int i;
  for(i=0; i<pSorter->nTask; i++){
    SortSubtask *pTask = &pSorter->aTask[i];





    int rc2 = vdbeSorterJoinThread(pTask, &pTask->thread);
    if( rc==SQLITE_OK ) rc = rc2;


  }
  return rc;
}
#else
# define vdbeSorterJoinAll(x,rcin) (rcin)
# define vdbeSorterJoinThread(pTask,p) SQLITE_OK
#endif

/*
** Allocate a new MergeEngine object with space for nIter iterators.
*/
static MergeEngine *vdbeMergeEngineNew(int nIter){
  int N = 2;                      /* Smallest power of two >= nIter */
  int nByte;                      /* Total bytes of space to allocate */
  MergeEngine *pNew;              /* Pointer to allocated object to return */

  assert( nIter<=SORTER_MAX_MERGE_COUNT );

  while( N<nIter ) N += N;
  nByte = sizeof(MergeEngine) + N * (sizeof(int) + sizeof(PmaReader));

  pNew = (MergeEngine*)sqlite3MallocZero(nByte);
  if( pNew ){
    pNew->nTree = N;
    pNew->aIter = (PmaReader*)&pNew[1];
................................................................................

/*
** Reset a sorting cursor back to its original empty state.
*/
void sqlite3VdbeSorterReset(sqlite3 *db, VdbeSorter *pSorter){
  int i;
  (void)vdbeSorterJoinAll(pSorter, SQLITE_OK);
  if( pSorter->pReader ){
    vdbePmaReaderClear(pSorter->pReader);
    sqlite3DbFree(db, pSorter->pReader);
    pSorter->pReader = 0;
  }
  vdbeMergeEngineFree(pSorter->pMerger);
  pSorter->pMerger = 0;
  for(i=0; i<pSorter->nTask; i++){
    SortSubtask *pTask = &pSorter->aTask[i];
    vdbeSortSubtaskCleanup(db, pTask);
  }
  if( pSorter->list.aMemory==0 ){
    vdbeSorterRecordFree(0, pSorter->list.pList);
  }
  pSorter->list.pList = 0;
  pSorter->list.szPMA = 0;
  pSorter->bUsePMA = 0;
  pSorter->iMemory = 0;
  pSorter->mxKeysize = 0;
  sqlite3DbFree(db, pSorter->pUnpacked);
  pSorter->pUnpacked = 0;
}

/*
** Free any cursor components allocated by sqlite3VdbeSorterXXX routines.
*/
void sqlite3VdbeSorterClose(sqlite3 *db, VdbeCursor *pCsr){
  VdbeSorter *pSorter = pCsr->pSorter;
  if( pSorter ){
    sqlite3VdbeSorterReset(db, pSorter);

    sqlite3_free(pSorter->list.aMemory);
    sqlite3DbFree(db, pSorter);
    pCsr->pSorter = 0;
  }
}

/*
** Allocate space for a file-handle and open a temporary file. If successful,
................................................................................
  );
  if( rc==SQLITE_OK ){
    i64 max = SQLITE_MAX_MMAP_SIZE;
    sqlite3OsFileControlHint( *ppFile, SQLITE_FCNTL_MMAP_SIZE, (void*)&max);
  }
  return rc;
}

static int vdbeSortAllocUnpacked(SortSubtask *pTask){
  if( pTask->pUnpacked==0 ){
    char *pFree;
    pTask->pUnpacked = sqlite3VdbeAllocUnpackedRecord(
        pTask->pKeyInfo, 0, 0, &pFree
    );
    assert( pTask->pUnpacked==(UnpackedRecord*)pFree );
    if( pFree==0 ) return SQLITE_NOMEM;
    pTask->pUnpacked->nField = pTask->pKeyInfo->nField;
    pTask->pUnpacked->errCode = 0;
  }
  return SQLITE_OK;
}


/*
** Merge the two sorted lists p1 and p2 into a single list.
** Set *ppOut to the head of the new list.
*/
static void vdbeSorterMerge(
  SortSubtask *pTask,             /* Calling thread context */
................................................................................
}

/*
** Sort the linked list of records headed at pTask->pList. Return 
** SQLITE_OK if successful, or an SQLite error code (i.e. SQLITE_NOMEM) if 
** an error occurs.
*/
static int vdbeSorterSort(SortSubtask *pTask, SorterList *pList){
  int i;
  SorterRecord **aSlot;
  SorterRecord *p;
  int rc;

  rc = vdbeSortAllocUnpacked(pTask);
  if( rc!=SQLITE_OK ) return rc;

  aSlot = (SorterRecord **)sqlite3MallocZero(64 * sizeof(SorterRecord *));
  if( !aSlot ){
    return SQLITE_NOMEM;
  }

  p = pList->pList;
  while( p ){
    SorterRecord *pNext;
    if( pList->aMemory ){
      if( (u8*)p==pList->aMemory ){
        pNext = 0;
      }else{
        assert( p->u.iNext<sqlite3MallocSize(pList->aMemory) );
        pNext = (SorterRecord*)&pList->aMemory[p->u.iNext];
      }
    }else{
      pNext = p->u.pNext;
    }

    p->u.pNext = 0;
    for(i=0; aSlot[i]; i++){
................................................................................
    p = pNext;
  }

  p = 0;
  for(i=0; i<64; i++){
    vdbeSorterMerge(pTask, p, aSlot[i], &p);
  }
  pList->pList = p;

  sqlite3_free(aSlot);
  if( pTask->pUnpacked->errCode ){
    assert( pTask->pUnpacked->errCode==SQLITE_NOMEM );
    return SQLITE_NOMEM;
  }
  return SQLITE_OK;
}

/*
** Initialize a PMA-writer object.
*/
static void vdbePmaWriterInit(
................................................................................
}
#else
# define vdbeSorterExtendFile(x,y,z) SQLITE_OK
#endif


/*
** Write the current contents of in-memory linked-list pList to a level-0
** PMA in the temp file belonging to sub-task pTask. Return SQLITE_OK if 
** successful, or an SQLite error code otherwise.
**
** The format of a PMA is:
**
**     * A varint. This varint contains the total number of bytes of content
**       in the PMA (not including the varint itself).
**
**     * One or more records packed end-to-end in order of ascending keys. 
**       Each record consists of a varint followed by a blob of data (the 
**       key). The varint is the number of bytes in the blob of data.
*/
static int vdbeSorterListToPMA(SortSubtask *pTask, SorterList *pList){
  int rc = SQLITE_OK;             /* Return code */
  PmaWriter writer;               /* Object used to write to the file */

#ifdef SQLITE_DEBUG
  /* Set iSz to the expected size of file pTask->file after writing the PMA. 
  ** This is used by an assert() statement at the end of this function.  */
  i64 iSz = pList->szPMA + sqlite3VarintLen(pList->szPMA) + pTask->file.iEof;
#endif

  vdbeSorterWorkDebug(pTask, "enter");
  memset(&writer, 0, sizeof(PmaWriter));

  assert( pList->szPMA>0 );

  /* If the first temporary PMA file has not been opened, open it now. */
  if( pTask->file.pFd==0 ){
    rc = vdbeSorterOpenTempFile(pTask->db->pVfs, &pTask->file.pFd);
    assert( rc!=SQLITE_OK || pTask->file.pFd );
    assert( pTask->file.iEof==0 );
    assert( pTask->nPMA==0 );
  }

  /* Try to get the file to memory map */
  if( rc==SQLITE_OK ){
    vdbeSorterExtendFile(pTask->db, 
        pTask->file.pFd, pTask->file.iEof + pList->szPMA + 9
    );
  }

  /* Sort the list */
  if( rc==SQLITE_OK ){
    rc = vdbeSorterSort(pTask, pList);
  }

  if( rc==SQLITE_OK ){
    SorterRecord *p;
    SorterRecord *pNext = 0;

    vdbePmaWriterInit(pTask->file.pFd, &writer, pTask->pgsz,
                      pTask->file.iEof);
    pTask->nPMA++;
    vdbePmaWriteVarint(&writer, pList->szPMA);
    for(p=pList->pList; p; p=pNext){
      pNext = p->u.pNext;
      vdbePmaWriteVarint(&writer, p->nVal);
      vdbePmaWriteBlob(&writer, SRVAL(p), p->nVal);
      if( pList->aMemory==0 ) sqlite3_free(p);
    }
    pList->pList = p;
    rc = vdbePmaWriterFinish(&writer, &pTask->file.iEof);
  }

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

/*
** Advance the MergeEngine iterator passed as the second argument to
** the next entry. Set *pbEof to true if this means the iterator has 
** reached EOF.
................................................................................

  return rc;
}

/*
** The main routine for sorter-thread operations.
*/
static void *vdbeSorterFlushThread(void *pCtx){

  SortSubtask *pTask = (SortSubtask*)pCtx;





  int rc;                         /* Return code */
  assert( pTask->thread.bDone==0 );





























































































  rc = vdbeSorterListToPMA(pTask, &pTask->list);





  pTask->thread.bDone = 1;




  return SQLITE_INT_TO_PTR(rc);
}

/*











** 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
  pSorter->bUsePMA = 1;
  return vdbeSorterListToPMA(&pSorter->aTask[0], &pSorter->list);
#else
  int rc = SQLITE_OK;
  int i;
  SortSubtask *pTask = 0;    /* Thread context used to create new PMA */
  int nWorker = (pSorter->nTask-1);

  /* Set the flag to indicate that at least one PMA has been written. 
  ** Or will be, anyhow.  */
  pSorter->bUsePMA = 1;

  /* Select a sub-task to sort and flush the current list of in-memory
  ** records to disk. If the sorter is running in multi-threaded mode,
  ** round-robin between the first (pSorter->nTask-1) tasks. Except, if
  ** the background thread from a sub-tasks previous turn is still running,
  ** skip it. If the first (pSorter->nTask-1) sub-tasks are all still busy,
  ** fall back to using the final sub-task. The first (pSorter->nTask-1)
  ** sub-tasks are prefered as they use background threads - the final 
  ** sub-task uses the main thread. */
  for(i=0; i<nWorker; i++){
    int iTest = (pSorter->iPrev + i + 1) % nWorker;
    pTask = &pSorter->aTask[iTest];

    if( pTask->thread.bDone ){

      rc = vdbeSorterJoinThread(pTask, &pTask->thread);
    }
    if( pTask->thread.pThread==0 || rc!=SQLITE_OK ) break;





  }

  if( rc==SQLITE_OK ){
    if( i==nWorker ){
      /* Use the foreground thread for this operation */
      rc = vdbeSorterListToPMA(&pSorter->aTask[nWorker], &pSorter->list);
    }else{
      /* Launch a background thread for this operation */
      u8 *aMem = pTask->list.aMemory;
      void *pCtx = (void*)pTask;

      assert( pTask->thread.pThread==0 && pTask->thread.bDone==0 );
      assert( pTask->list.pList==0 );
      assert( pTask->list.aMemory==0 || pSorter->list.aMemory!=0 );

      pSorter->iPrev = (pTask - pSorter->aTask);




      pTask->list = pSorter->list;

      pSorter->list.pList = 0;
      pSorter->list.szPMA = 0;




      if( aMem ){
        pSorter->list.aMemory = aMem;









        pSorter->nMemory = sqlite3MallocSize(aMem);

      }else{
        pSorter->list.aMemory = sqlite3Malloc(pSorter->nMemory);
        if( !pSorter->list.aMemory ) return SQLITE_NOMEM;
      }













      rc = vdbeSorterCreateThread(&pTask->thread, vdbeSorterFlushThread, pCtx);
    }
  }

  return rc;
#endif
}

/*
** Add a record to the sorter.
*/
int sqlite3VdbeSorterWrite(
  sqlite3 *db,                    /* Database handle */
................................................................................
  **
  **   * The total memory allocated for the in-memory list is greater 
  **     than (page-size * 10) and sqlite3HeapNearlyFull() returns true.
  */
  nReq = pVal->n + sizeof(SorterRecord);
  nPMA = pVal->n + sqlite3VarintLen(pVal->n);
  if( pSorter->mxPmaSize ){
    if( pSorter->list.aMemory ){
      bFlush = pSorter->iMemory && (pSorter->iMemory+nReq) > pSorter->mxPmaSize;
    }else{
      bFlush = (
          (pSorter->list.szPMA > pSorter->mxPmaSize)
       || (pSorter->list.szPMA > pSorter->mnPmaSize && sqlite3HeapNearlyFull())
      );
    }
    if( bFlush ){
      rc = vdbeSorterFlushPMA(pSorter);
      pSorter->list.szPMA = 0;
      pSorter->iMemory = 0;
      assert( rc!=SQLITE_OK || pSorter->list.pList==0 );
    }
  }

  pSorter->list.szPMA += nPMA;
  if( nPMA>pSorter->mxKeysize ){
    pSorter->mxKeysize = nPMA;
  }

  if( pSorter->list.aMemory ){
    int nMin = pSorter->iMemory + nReq;

    if( nMin>pSorter->nMemory ){
      u8 *aNew;
      int nNew = pSorter->nMemory * 2;
      while( nNew < nMin ) nNew = nNew*2;
      if( nNew > pSorter->mxPmaSize ) nNew = pSorter->mxPmaSize;
      if( nNew < nMin ) nNew = nMin;

      aNew = sqlite3Realloc(pSorter->list.aMemory, nNew);
      if( !aNew ) return SQLITE_NOMEM;
      pSorter->list.pList = (SorterRecord*)(
          aNew + ((u8*)pSorter->list.pList - pSorter->list.aMemory)
      );
      pSorter->list.aMemory = aNew;
      pSorter->nMemory = nNew;
    }

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

  memcpy(SRVAL(pNew), pVal->z, pVal->n);
  pNew->nVal = pVal->n;
  pSorter->list.pList = pNew;

  return rc;
}

/*
** Read keys from pIncr->pMerger and populate pIncr->aFile[1]. The format
** of the data stored in aFile[1] is the same as that used by regular PMAs,
** except that the number-of-bytes varint is omitted from the start.
*/
static int vdbeIncrPopulate(IncrMerger *pIncr){
  int rc = SQLITE_OK;
  int rc2;
  i64 iStart = pIncr->iStartOff;
  SorterFile *pOut = &pIncr->aFile[1];
  MergeEngine *pMerger = pIncr->pMerger;
  PmaWriter writer;
  assert( pIncr->bEof==0 );

  vdbeSorterPopulateDebug(pIncr->pTask, "enter");

  vdbePmaWriterInit(pOut->pFd, &writer, pIncr->pTask->pgsz, iStart);
  while( rc==SQLITE_OK ){
    int dummy;
    PmaReader *pReader = &pMerger->aIter[ pMerger->aTree[1] ];
    int nKey = pReader->nKey;
    i64 iEof = writer.iWriteOff + writer.iBufEnd;

    /* Check if the output file is full or if the input has been exhausted.
    ** In either case exit the loop. */
    if( pReader->pFile==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 = vdbeSorterNext(pIncr->pTask, pIncr->pMerger, &dummy);
  }

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

static void *vdbeIncrPopulateThread(void *pCtx){
  IncrMerger *pIncr = (IncrMerger*)pCtx;
  void *pRet = SQLITE_INT_TO_PTR( vdbeIncrPopulate(pIncr) );
  pIncr->thread.bDone = 1;
  return pRet;
}

#if SQLITE_MAX_WORKER_THREADS>0
static int vdbeIncrBgPopulate(IncrMerger *pIncr){
  void *pCtx = (void*)pIncr;
  assert( pIncr->bUseThread );
  return vdbeSorterCreateThread(&pIncr->thread, vdbeIncrPopulateThread, pCtx);
}
#endif

static int vdbeIncrSwap(IncrMerger *pIncr){
  int rc = SQLITE_OK;

#if SQLITE_MAX_WORKER_THREADS>0
  if( pIncr->bUseThread ){
    rc = vdbeSorterJoinThread(pIncr->pTask, &pIncr->thread);

    if( rc==SQLITE_OK ){
      SorterFile f0 = pIncr->aFile[0];
      pIncr->aFile[0] = pIncr->aFile[1];
      pIncr->aFile[1] = f0;
    }

    if( rc==SQLITE_OK ){
      if( pIncr->aFile[0].iEof==pIncr->iStartOff ){
        pIncr->bEof = 1;
      }else{
        rc = vdbeIncrBgPopulate(pIncr);
      }
    }
  }else
#endif
  {
    rc = vdbeIncrPopulate(pIncr);
    pIncr->aFile[0] = pIncr->aFile[1];
    if( pIncr->aFile[0].iEof==pIncr->iStartOff ){
      pIncr->bEof = 1;
    }
  }

  return rc;
}

static void vdbeIncrFree(IncrMerger *pIncr){
  if( pIncr ){
#if SQLITE_MAX_WORKER_THREADS>0
    vdbeSorterJoinThread(pIncr->pTask, &pIncr->thread);
    if( pIncr->bUseThread ){
      if( pIncr->aFile[0].pFd ) sqlite3OsCloseFree(pIncr->aFile[0].pFd);
      if( pIncr->aFile[1].pFd ) sqlite3OsCloseFree(pIncr->aFile[1].pFd);
    }
#endif
    vdbeMergeEngineFree(pIncr->pMerger);
    sqlite3_free(pIncr);
  }
}

static IncrMerger *vdbeIncrNew(SortSubtask *pTask, MergeEngine *pMerger){
  IncrMerger *pIncr = sqlite3_malloc(sizeof(IncrMerger));
  if( pIncr ){
    memset(pIncr, 0, sizeof(IncrMerger));
    pIncr->pMerger = pMerger;
    pIncr->pTask = pTask;
    pIncr->mxSz = MAX(pTask->pSorter->mxKeysize+9,pTask->pSorter->mxPmaSize/2);
    pTask->file2.iEof += pIncr->mxSz;
  }
  return pIncr;
}

static void vdbeIncrSetThreads(IncrMerger *pIncr, int bUseThread){
  if( bUseThread ){
    pIncr->bUseThread = 1;
    pIncr->pTask->file2.iEof -= pIncr->mxSz;
  }
}

#define INCRINIT2_NORMAL 0
#define INCRINIT2_TASK   1
#define INCRINIT2_ROOT   2

static int vdbeIncrInit2(PmaReader *pIter, int eMode);

static int vdbeIncrInitMerger(
  SortSubtask *pTask, 
  MergeEngine *pMerger, 
  int eMode
){
  int i;
  int rc = SQLITE_OK;

  for(i=0; rc==SQLITE_OK && i<pMerger->nTree; i++){
    if( eMode==INCRINIT2_ROOT ){
      rc = vdbePmaReaderNext(&pMerger->aIter[i]);
    }else{
      rc = vdbeIncrInit2(&pMerger->aIter[i], INCRINIT2_NORMAL);
    }
  }

  for(i=pMerger->nTree-1; rc==SQLITE_OK && i>0; i--){
    rc = vdbeSorterDoCompare(pTask, pMerger, i);
  }

  return rc;
}

static int vdbeIncrInit2(PmaReader *pIter, int eMode){
  int rc = SQLITE_OK;
  IncrMerger *pIncr = pIter->pIncr;
  if( pIncr ){
    SortSubtask *pTask = pIncr->pTask;

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

    /* Set up the required files for pIncr */
    if( rc==SQLITE_OK ){
      if( pIncr->bUseThread==0 ){
        if( pTask->file2.pFd==0 ){
          rc = vdbeSorterOpenTempFile(pTask->db->pVfs, &pTask->file2.pFd);
          assert( pTask->file2.iEof>0 );
          if( rc==SQLITE_OK ){
            vdbeSorterExtendFile(pTask->db,pTask->file2.pFd,pTask->file2.iEof);
            pTask->file2.iEof = 0;
          }
        }
        if( rc==SQLITE_OK ){
          pIncr->aFile[1].pFd = pTask->file2.pFd;
          pIncr->iStartOff = pTask->file2.iEof;
          pTask->file2.iEof += pIncr->mxSz;
        }
      }else{
        rc = vdbeSorterOpenTempFile(pTask->db->pVfs, &pIncr->aFile[0].pFd);
        if( rc==SQLITE_OK ){
          rc = vdbeSorterOpenTempFile(pTask->db->pVfs, &pIncr->aFile[1].pFd);
        }
      }
    }

    if( rc==SQLITE_OK && pIncr->bUseThread ){
      /* Use the current thread */
      assert( eMode==INCRINIT2_ROOT || eMode==INCRINIT2_TASK );
      rc = vdbeIncrPopulate(pIncr);
    }

    if( rc==SQLITE_OK && eMode!=INCRINIT2_TASK ){
      rc = vdbePmaReaderNext(pIter);
    }
  }
  return rc;
}

#if SQLITE_MAX_WORKER_THREADS>0
static void *vdbeIncrInit2Thread(void *pCtx){
  PmaReader *pReader = (PmaReader*)pCtx;
  void *pRet = SQLITE_INT_TO_PTR( vdbeIncrInit2(pReader, INCRINIT2_TASK) );
  pReader->pIncr->thread.bDone = 1;
  return pRet;
}

static int vdbeIncrBgInit2(PmaReader *pIter){
  void *pCtx = (void*)pIter;
  return vdbeSorterCreateThread(
      &pIter->pIncr->thread, vdbeIncrInit2Thread, pCtx
  );
}
#endif

/*
** Allocate a new MergeEngine object to merge the contents of nPMA level-0
** PMAs from pTask->file. If no error occurs, set *ppOut to point to
** the new object and return SQLITE_OK. Or, if an error does occur, set *ppOut
** to NULL and return an SQLite error code.
**
** When this function is called, *piOffset is set to the offset of the
** first PMA to read from pTask->file. Assuming no error occurs, it is 
** set to the offset immediately following the last byte of the last
** PMA before returning. If an error does occur, then the final value of
** *piOffset is undefined.
*/
static int vdbeMergeEngineLevel0(
  SortSubtask *pTask,             /* Sorter task to read from */
  int nPMA,                       /* Number of PMAs to read */
  i64 *piOffset,                  /* IN/OUT: Read offset in pTask->file */
  MergeEngine **ppOut             /* OUT: New merge-engine */
){
  MergeEngine *pNew;              /* Merge engine to return */
  i64 iOff = *piOffset;
  int i;
  int rc = SQLITE_OK;

  *ppOut = pNew = vdbeMergeEngineNew(nPMA);
  if( pNew==0 ) rc = SQLITE_NOMEM;

  for(i=0; i<nPMA && rc==SQLITE_OK; i++){
    i64 nDummy;
    PmaReader *pIter = &pNew->aIter[i];
    rc = vdbePmaReaderInit(pTask, &pTask->file, iOff, pIter, &nDummy);
    iOff = pIter->iEof;
  }

  if( rc!=SQLITE_OK ){
    vdbeMergeEngineFree(pNew);
    *ppOut = 0;
  }
  *piOffset = iOff;
  return rc;
}

typedef struct IncrBuilder IncrBuilder;
struct IncrBuilder {
  int nPMA;                     /* Number of iterators used so far */
  MergeEngine *pMerger;         /* Merge engine to populate. */
};

static int vdbeAddToBuilder(
  SortSubtask *pTask,
  IncrBuilder *pBuilder, 
  MergeEngine *pMerger
){
  int rc = SQLITE_OK;
  IncrMerger *pIncr;

  assert( pMerger );
  if( pBuilder->nPMA==SORTER_MAX_MERGE_COUNT ){
    rc = vdbeAddToBuilder(pTask, &pBuilder[1], pBuilder->pMerger);
    pBuilder->pMerger = 0;
    pBuilder->nPMA = 0;
  }

  if( rc==SQLITE_OK && pBuilder->pMerger==0 ){
    pBuilder->pMerger = vdbeMergeEngineNew(SORTER_MAX_MERGE_COUNT);
    if( pBuilder->pMerger==0 ) rc = SQLITE_NOMEM;
  }

  if( rc==SQLITE_OK ){
    pIncr = vdbeIncrNew(pTask, pMerger);
    if( pIncr==0 ) rc = SQLITE_NOMEM;
    pBuilder->pMerger->aIter[pBuilder->nPMA++].pIncr = pIncr;
  }

  if( rc!=SQLITE_OK ){
    vdbeMergeEngineFree(pMerger);
  }

  return rc;
}

/*
** Populate iterator *pIter so that it may be used to iterate through all 
** keys stored in all PMAs created by this sorter.
*/
static int vdbePmaReaderIncrInit(VdbeSorter *pSorter){
  SortSubtask *pTask0 = &pSorter->aTask[0];
  MergeEngine *pMain = 0;
  sqlite3 *db = pTask0->db;
  int rc = SQLITE_OK;
  int iTask;

  IncrBuilder *aMerge;
  const int nMerge = 32;
  aMerge = sqlite3DbMallocZero(db, sizeof(aMerge[0])*nMerge);
  if( aMerge==0 ) return SQLITE_NOMEM;

  if( pSorter->nTask>1 ){
    pMain = vdbeMergeEngineNew(pSorter->nTask);
    if( pMain==0 ) rc = SQLITE_NOMEM;
  }

  for(iTask=0; iTask<pSorter->nTask && rc==SQLITE_OK; iTask++){
    MergeEngine *pRoot = 0;
    int iPMA;
    i64 iReadOff = 0;
    SortSubtask *pTask = &pSorter->aTask[iTask];
    if( pTask->nPMA==0 ) continue;
    for(iPMA=0; iPMA<pTask->nPMA; iPMA += SORTER_MAX_MERGE_COUNT){
      MergeEngine *pMerger = 0;
      int nReader = MIN(pTask->nPMA - iPMA, SORTER_MAX_MERGE_COUNT);

      rc = vdbeMergeEngineLevel0(pTask, nReader, &iReadOff, &pMerger);
      if( rc!=SQLITE_OK ) break;

      if( iPMA==0 ){
        pRoot = pMerger;
      }else{
        if( pRoot ){
          rc = vdbeAddToBuilder(pTask, &aMerge[0], pRoot);
          pRoot = 0;
          if( rc!=SQLITE_OK ){
            vdbeMergeEngineFree(pMerger);
            break;
          }
        }
        rc = vdbeAddToBuilder(pTask, &aMerge[0], pMerger);
      }
    }

    if( pRoot==0 ){
      int i;
      for(i=0; rc==SQLITE_OK && i<nMerge; i++){
        if( aMerge[i].pMerger ){
          if( pRoot ){
            rc = vdbeAddToBuilder(pTask, &aMerge[i], pRoot);
            if( rc!=SQLITE_OK ) break;
          }
          pRoot = aMerge[i].pMerger;
          aMerge[i].pMerger = 0;
        }
      }
    }

    if( rc==SQLITE_OK ){
      if( pMain==0 ){
        pMain = pRoot;
      }else{
        IncrMerger *pNew = vdbeIncrNew(pTask, pRoot);
        pMain->aIter[iTask].pIncr = pNew;
        if( pNew==0 ) rc = SQLITE_NOMEM;
      }
      memset(aMerge, 0, nMerge*sizeof(aMerge[0]));
    }
  }

  if( rc==SQLITE_OK ){
#if SQLITE_MAX_WORKER_THREADS
    if( pSorter->bUseThreads ){
      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;
      }
      if( rc==SQLITE_OK ){
        pIter->pIncr = vdbeIncrNew(pLast, pMain);
        if( pIter->pIncr==0 ){
          rc = SQLITE_NOMEM;
        }
        else{
          vdbeIncrSetThreads(pIter->pIncr, pSorter->bUseThreads);
          for(iTask=0; iTask<(pSorter->nTask-1); iTask++){
            IncrMerger *pIncr;
            if( (pIncr = pMain->aIter[iTask].pIncr) ){
              vdbeIncrSetThreads(pIncr, pSorter->bUseThreads);
              assert( pIncr->pTask!=pLast );
            }
          }
          if( pSorter->nTask>1 ){
            for(iTask=0; rc==SQLITE_OK && iTask<pSorter->nTask; iTask++){
              PmaReader *p = &pMain->aIter[iTask];
              assert( p->pIncr==0 || p->pIncr->pTask==&pSorter->aTask[iTask] );
              if( p->pIncr ){ rc = vdbeIncrBgInit2(p); }
            }
          }
        }
      }
      if( rc==SQLITE_OK ){
        int eMode = (pSorter->nTask>1 ? INCRINIT2_ROOT : INCRINIT2_NORMAL);
        rc = vdbeIncrInit2(pIter, eMode);
      }
    }else
#endif
    {
      pSorter->pMerger = pMain;
      rc = vdbeIncrInitMerger(pTask0, pMain, INCRINIT2_NORMAL);
    }
  }

  sqlite3_free(aMerge);
  return rc;
}


/*
** 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(sqlite3 *db, const VdbeCursor *pCsr, int *pbEof){
................................................................................

  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->bUsePMA==0 ){
    if( pSorter->list.pList ){

      *pbEof = 0;








      rc = vdbeSorterSort(&pSorter->aTask[0], &pSorter->list);
    }else{
      *pbEof = 1;
    }
    return rc;
  }

  /* Write the current in-memory list to a PMA. */
  if( pSorter->list.pList ){
    rc = vdbeSorterFlushPMA(pSorter);
  }

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

  vdbeSorterRewindDebug(db, "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 = vdbePmaReaderIncrInit(pSorter);

    *pbEof = 0;
  }











  vdbeSorterRewindDebug(db, "rewinddone");
  return rc;
}

/*
** Advance to the next element in the sorter.
*/
int sqlite3VdbeSorterNext(sqlite3 *db, const VdbeCursor *pCsr, int *pbEof){
  VdbeSorter *pSorter = pCsr->pSorter;
  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( pSorter->bUseThreads ){
      rc = vdbePmaReaderNext(pSorter->pReader);
      *pbEof = (pSorter->pReader->pFile==0);
    }else{
      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);
    *pbEof = !pSorter->list.pList;
    rc = SQLITE_OK;
  }
  return rc;
}

/*
** Return a pointer to a buffer owned by the sorter that contains the 
................................................................................
** current key.
*/
static void *vdbeSorterRowkey(
  const VdbeSorter *pSorter,      /* Sorter object */
  int *pnKey                      /* OUT: Size of current key in bytes */
){
  void *pKey;
  if( pSorter->bUsePMA ){
    PmaReader *pReader = (pSorter->bUseThreads ?
        pSorter->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;
}

/*
** Copy the current sorter key into the memory cell pOut.
*/
................................................................................
int sqlite3VdbeSorterCompare(
  const VdbeCursor *pCsr,         /* Sorter cursor */
  Mem *pVal,                      /* Value to compare to current sorter key */
  int nIgnore,                    /* Ignore this many fields at the end */
  int *pRes                       /* OUT: Result of comparison */
){
  VdbeSorter *pSorter = pCsr->pSorter;
  UnpackedRecord *r2 = pSorter->pUnpacked;
  KeyInfo *pKeyInfo = pCsr->pKeyInfo;
  int i;
  void *pKey; int nKey;           /* Sorter key to compare pVal with */

  if( r2==0 ){
    char *p;
    r2 = pSorter->pUnpacked = sqlite3VdbeAllocUnpackedRecord(pKeyInfo,0,0,&p);
    assert( pSorter->pUnpacked==(UnpackedRecord*)p );
    if( r2==0 ) return SQLITE_NOMEM;
    r2->nField = pKeyInfo->nField-nIgnore;
  }
  assert( r2->nField>=pKeyInfo->nField-nIgnore );

  pKey = vdbeSorterRowkey(pSorter, &nKey);
  sqlite3VdbeRecordUnpack(pKeyInfo, nKey, pKey, r2);
  for(i=0; i<r2->nField; i++){
    if( r2->aMem[i].flags & MEM_Null ){
      *pRes = -1;
      return SQLITE_OK;
    }
  }

  *pRes = sqlite3VdbeRecordCompare(pVal->n, pVal->z, r2, 0);
  return SQLITE_OK;
}

Changes to test/sort2.test.

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# This file implements regression tests for SQLite library. 
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix sort2




db close
sqlite3_shutdown
sqlite3_config_worker_threads 7
reset_db





do_execsql_test 1 {
  PRAGMA cache_size = 5;
  WITH r(x,y) AS (
    SELECT 1, randomblob(100)
    UNION ALL
    SELECT x+1, randomblob(100) FROM r
    LIMIT 100000
  )
  SELECT count(x), length(y) FROM r GROUP BY (x%5)
} {
  20000 100 20000 100 20000 100 20000 100 20000 100
}

do_execsql_test 2.1 {
  CREATE TABLE t1(a, b);
  WITH r(x,y) AS (
    SELECT 1, randomblob(100)
    UNION ALL
    SELECT x+1, randomblob(100) FROM r
    LIMIT 10000
  ) INSERT INTO t1 SELECT * FROM r;
}

do_execsql_test 2.2 {
  CREATE UNIQUE INDEX i1 ON t1(b, a);
}





















db close
sqlite3_shutdown
sqlite3_config_worker_threads 0
sqlite3_initialize



finish_test








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# This file implements regression tests for SQLite library. 
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix sort2

foreach {tn script} {
  1 { }
  2 {
    catch { db close }
    sqlite3_shutdown
    sqlite3_config_worker_threads 7
    reset_db
  }
} {

  eval $script

  do_execsql_test $tn.1 {
    PRAGMA cache_size = 5;
    WITH r(x,y) AS (
      SELECT 1, randomblob(100)
      UNION ALL
      SELECT x+1, randomblob(100) FROM r
      LIMIT 100000
    )
    SELECT count(x), length(y) FROM r GROUP BY (x%5)
  } {
    20000 100 20000 100 20000 100 20000 100 20000 100
  }

  do_execsql_test $tn.2.1 {
    CREATE TABLE t1(a, b);
    WITH r(x,y) AS (
      SELECT 1, randomblob(100)
      UNION ALL
      SELECT x+1, randomblob(100) FROM r
      LIMIT 10000
    ) INSERT INTO t1 SELECT * FROM r;
  }
  
  do_execsql_test $tn.2.2 {
    CREATE UNIQUE INDEX i1 ON t1(b, a);
  }
  
  do_execsql_test $tn.2.3 {
    CREATE UNIQUE INDEX i2 ON t1(a);
  }
  
  do_execsql_test $tn.2.4 { PRAGMA integrity_check } {ok}
  
  breakpoint
  do_execsql_test $tn.3 {
    PRAGMA cache_size = 5;
    WITH r(x,y) AS (
      SELECT 1, randomblob(100)
      UNION ALL
      SELECT x+1, randomblob(100) FROM r
      LIMIT 1000000
    )
    SELECT count(x), length(y) FROM r GROUP BY (x%5)
  } {
    200000 100 200000 100 200000 100 200000 100 200000 100
  }
  
  db close
  sqlite3_shutdown
  sqlite3_config_worker_threads 0
  sqlite3_initialize

}

finish_test