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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Improve performance of multi-field sorts where the first field has a low cardinality.
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SHA1: 601e7b6b8e6bfabda03b70f75094c9014e3a3c49
User & Date: dan 2015-03-30 12:06:26
Context
2015-04-01
16:18
Reduce the CPU used by CREATE INDEX statements by taking better advantage of the fact that keys are inserted in sorted order. check-in: 592cdc5d user: dan tags: sorter-opt
2015-03-30
19:56
Optimize CREATE INDEX, REINDEX and VACUUM statements by taking better advantage of the fact that index keys are being inserted into b-trees in sorted order. Leaf check-in: 763d2bc7 user: dan tags: mistake
15:45
Merge sorter optimizations with this branch. check-in: 9bf1cfb4 user: dan tags: insert-select-opt
12:06
Improve performance of multi-field sorts where the first field has a low cardinality. check-in: 601e7b6b user: dan tags: sorter-opt
09:58
Remove some unnecessary code from vdbesort.c. check-in: b58191e9 user: dan tags: sorter-opt
Changes
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Changes to src/vdbe.h.

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#ifndef SQLITE_OMIT_TRACE
  char *sqlite3VdbeExpandSql(Vdbe*, const char*);
#endif
int sqlite3MemCompare(const Mem*, const Mem*, const CollSeq*);

void sqlite3VdbeRecordUnpack(KeyInfo*,int,const void*,UnpackedRecord*);
int sqlite3VdbeRecordCompare(int,const void*,UnpackedRecord*);

UnpackedRecord *sqlite3VdbeAllocUnpackedRecord(KeyInfo *, char *, int, char **);

typedef int (*RecordCompare)(int,const void*,UnpackedRecord*);
RecordCompare sqlite3VdbeFindCompare(UnpackedRecord*);

#ifndef SQLITE_OMIT_TRIGGER
void sqlite3VdbeLinkSubProgram(Vdbe *, SubProgram *);







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#ifndef SQLITE_OMIT_TRACE
  char *sqlite3VdbeExpandSql(Vdbe*, const char*);
#endif
int sqlite3MemCompare(const Mem*, const Mem*, const CollSeq*);

void sqlite3VdbeRecordUnpack(KeyInfo*,int,const void*,UnpackedRecord*);
int sqlite3VdbeRecordCompare(int,const void*,UnpackedRecord*);
int sqlite3VdbeRecordCompareWithSkip(int, const void *, UnpackedRecord *, int);
UnpackedRecord *sqlite3VdbeAllocUnpackedRecord(KeyInfo *, char *, int, char **);

typedef int (*RecordCompare)(int,const void*,UnpackedRecord*);
RecordCompare sqlite3VdbeFindCompare(UnpackedRecord*);

#ifndef SQLITE_OMIT_TRIGGER
void sqlite3VdbeLinkSubProgram(Vdbe *, SubProgram *);

Changes to src/vdbeaux.c.

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** returned.
**
** If database corruption is discovered, set pPKey2->errCode to 
** SQLITE_CORRUPT and return 0. If an OOM error is encountered, 
** pPKey2->errCode is set to SQLITE_NOMEM and, if it is not NULL, the
** malloc-failed flag set on database handle (pPKey2->pKeyInfo->db).
*/
static int vdbeRecordCompareWithSkip(
  int nKey1, const void *pKey1,   /* Left key */
  UnpackedRecord *pPKey2,         /* Right key */
  int bSkip                       /* If true, skip the first field */
){
  u32 d1;                         /* Offset into aKey[] of next data element */
  int i;                          /* Index of next field to compare */
  u32 szHdr1;                     /* Size of record header in bytes */
................................................................................
  );
  return pPKey2->default_rc;
}
int sqlite3VdbeRecordCompare(
  int nKey1, const void *pKey1,   /* Left key */
  UnpackedRecord *pPKey2          /* Right key */
){
  return vdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 0);
}


/*
** This function is an optimized version of sqlite3VdbeRecordCompare() 
** that (a) the first field of pPKey2 is an integer, and (b) the 
** size-of-header varint at the start of (pKey1/nKey1) fits in a single
................................................................................
  if( v>lhs ){
    res = pPKey2->r1;
  }else if( v<lhs ){
    res = pPKey2->r2;
  }else if( pPKey2->nField>1 ){
    /* The first fields of the two keys are equal. Compare the trailing 
    ** fields.  */
    res = vdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
  }else{
    /* The first fields of the two keys are equal and there are no trailing
    ** fields. Return pPKey2->default_rc in this case. */
    res = pPKey2->default_rc;
  }

  assert( vdbeRecordCompareDebug(nKey1, pKey1, pPKey2, res) );
................................................................................
    nCmp = MIN( pPKey2->aMem[0].n, nStr );
    res = memcmp(&aKey1[szHdr], pPKey2->aMem[0].z, nCmp);

    if( res==0 ){
      res = nStr - pPKey2->aMem[0].n;
      if( res==0 ){
        if( pPKey2->nField>1 ){
          res = vdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
        }else{
          res = pPKey2->default_rc;
        }
      }else if( res>0 ){
        res = pPKey2->r2;
      }else{
        res = pPKey2->r1;







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** returned.
**
** If database corruption is discovered, set pPKey2->errCode to 
** SQLITE_CORRUPT and return 0. If an OOM error is encountered, 
** pPKey2->errCode is set to SQLITE_NOMEM and, if it is not NULL, the
** malloc-failed flag set on database handle (pPKey2->pKeyInfo->db).
*/
int sqlite3VdbeRecordCompareWithSkip(
  int nKey1, const void *pKey1,   /* Left key */
  UnpackedRecord *pPKey2,         /* Right key */
  int bSkip                       /* If true, skip the first field */
){
  u32 d1;                         /* Offset into aKey[] of next data element */
  int i;                          /* Index of next field to compare */
  u32 szHdr1;                     /* Size of record header in bytes */
................................................................................
  );
  return pPKey2->default_rc;
}
int sqlite3VdbeRecordCompare(
  int nKey1, const void *pKey1,   /* Left key */
  UnpackedRecord *pPKey2          /* Right key */
){
  return sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 0);
}


/*
** This function is an optimized version of sqlite3VdbeRecordCompare() 
** that (a) the first field of pPKey2 is an integer, and (b) the 
** size-of-header varint at the start of (pKey1/nKey1) fits in a single
................................................................................
  if( v>lhs ){
    res = pPKey2->r1;
  }else if( v<lhs ){
    res = pPKey2->r2;
  }else if( pPKey2->nField>1 ){
    /* The first fields of the two keys are equal. Compare the trailing 
    ** fields.  */
    res = sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
  }else{
    /* The first fields of the two keys are equal and there are no trailing
    ** fields. Return pPKey2->default_rc in this case. */
    res = pPKey2->default_rc;
  }

  assert( vdbeRecordCompareDebug(nKey1, pKey1, pPKey2, res) );
................................................................................
    nCmp = MIN( pPKey2->aMem[0].n, nStr );
    res = memcmp(&aKey1[szHdr], pPKey2->aMem[0].z, nCmp);

    if( res==0 ){
      res = nStr - pPKey2->aMem[0].n;
      if( res==0 ){
        if( pPKey2->nField>1 ){
          res = sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
        }else{
          res = pPKey2->default_rc;
        }
      }else if( res>0 ){
        res = pPKey2->r2;
      }else{
        res = pPKey2->r1;

Changes to src/vdbesort.c.

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  }

  if( rc==SQLITE_OK ){
    rc = vdbePmaReaderNext(pReadr);
  }
  return rc;
}




















/*
** Compare key1 (buffer pKey1, size nKey1 bytes) with key2 (buffer pKey2, 
** size nKey2 bytes). Use (pTask->pKeyInfo) for the collation sequences
** used by the comparison. Return the result of the comparison.
**
** If IN/OUT parameter *pbKey2Cached is true when this function is called,
................................................................................
  res = memcmp(v1, v2, MIN(n1, n2));
  if( res==0 ){
    res = n1 - n2;
  }

  if( res==0 ){
    if( pTask->pSorter->pKeyInfo->nField>1 ){

      res = vdbeSorterCompare(pTask, pbKey2Cached, pKey1, nKey1, pKey2, nKey2);

    }
  }else{
    if( pTask->pSorter->pKeyInfo->aSortOrder[0] ){
      res = res * -1;
    }
  }

................................................................................
        if( *v2 & 0x80 ) res = +1;
      }
    }
  }

  if( res==0 ){
    if( pTask->pSorter->pKeyInfo->nField>1 ){

      res = vdbeSorterCompare(pTask, pbKey2Cached, pKey1, nKey1, pKey2, nKey2);

    }
  }else if( pTask->pSorter->pKeyInfo->aSortOrder[0] ){
    res = res * -1;
  }

  return res;
}







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  }

  if( rc==SQLITE_OK ){
    rc = vdbePmaReaderNext(pReadr);
  }
  return rc;
}

/*
** A version of vdbeSorterCompare() that assumes that it has already been
** determined that the first field of key1 is equal to the first field of 
** key2.
*/
static int vdbeSorterCompareTail(
  SortSubtask *pTask,             /* Subtask context (for pKeyInfo) */
  int *pbKey2Cached,              /* True if pTask->pUnpacked is pKey2 */
  const void *pKey1, int nKey1,   /* Left side of comparison */
  const void *pKey2, int nKey2    /* Right side of comparison */
){
  UnpackedRecord *r2 = pTask->pUnpacked;
  if( *pbKey2Cached==0 ){
    sqlite3VdbeRecordUnpack(pTask->pSorter->pKeyInfo, nKey2, pKey2, r2);
    *pbKey2Cached = 1;
  }
  return sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, r2, 1);
}

/*
** Compare key1 (buffer pKey1, size nKey1 bytes) with key2 (buffer pKey2, 
** size nKey2 bytes). Use (pTask->pKeyInfo) for the collation sequences
** used by the comparison. Return the result of the comparison.
**
** If IN/OUT parameter *pbKey2Cached is true when this function is called,
................................................................................
  res = memcmp(v1, v2, MIN(n1, n2));
  if( res==0 ){
    res = n1 - n2;
  }

  if( res==0 ){
    if( pTask->pSorter->pKeyInfo->nField>1 ){
      res = vdbeSorterCompareTail(
          pTask, pbKey2Cached, pKey1, nKey1, pKey2, nKey2
      );
    }
  }else{
    if( pTask->pSorter->pKeyInfo->aSortOrder[0] ){
      res = res * -1;
    }
  }

................................................................................
        if( *v2 & 0x80 ) res = +1;
      }
    }
  }

  if( res==0 ){
    if( pTask->pSorter->pKeyInfo->nField>1 ){
      res = vdbeSorterCompareTail(
          pTask, pbKey2Cached, pKey1, nKey1, pKey2, nKey2
      );
    }
  }else if( pTask->pSorter->pKeyInfo->aSortOrder[0] ){
    res = res * -1;
  }

  return res;
}