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Comment:Make sure that the sorting-index pre-filter recognizes that a rowid reference might be sortable. This fixes a performance regression.
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SHA1:72727b68cd07969165f1f0943cc7e1a265436653
User & Date: drh 2014-09-19 02:01:37
Context
2014-09-19
04:42
Add the sqlite3VdbeMemClearAndResize() function. Fix a sorting-index prefilter problem. check-in: 987a7a21 user: drh tags: trunk
02:01
Make sure that the sorting-index pre-filter recognizes that a rowid reference might be sortable. This fixes a performance regression. Closed-Leaf check-in: 72727b68 user: drh tags: Cplusplus-comment
00:43
Add the sqlite3VdbeMemClearAndResize() interface to be used in place of sqlite3VdbeMemGrow(). A C++ style comment was left in this check-in by mistake, and so it has been moved into a branch to avoid problems in any future bisects on windows. check-in: 5b9b8987 user: drh tags: Cplusplus-comment
Changes
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Changes to src/where.c.

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/*
** Return True if it is possible that pIndex might be useful in
** implementing the ORDER BY clause in pBuilder.
**
** Return False if pBuilder does not contain an ORDER BY clause or
** if there is no way for pIndex to be useful in implementing that
** ORDER BY clause.
*/
static int indexMightHelpWithOrderBy(
  WhereLoopBuilder *pBuilder,
  Index *pIndex,
  int iCursor
){
  ExprList *pOB;
  int ii, jj;

  if( pIndex->bUnordered ) return 0;
  if( (pOB = pBuilder->pWInfo->pOrderBy)==0 ) return 0;
  for(ii=0; ii<pOB->nExpr; ii++){
    Expr *pExpr = sqlite3ExprSkipCollate(pOB->a[ii].pExpr);
    if( pExpr->op!=TK_COLUMN ) return 0;
    if( pExpr->iTable==iCursor ){

      for(jj=0; jj<pIndex->nKeyCol; jj++){
        if( pExpr->iColumn==pIndex->aiColumn[jj] ) return 1;
      }
    }
  }
  return 0;
}

/*
** Return a bitmask where 1s indicate that the corresponding column of
** the table is used by an index.  Only the first 63 columns are considered.
*/
static Bitmask columnsInIndex(Index *pIdx){
  Bitmask m = 0;
  int j;
  for(j=pIdx->nColumn-1; j>=0; j--){
    int x = pIdx->aiColumn[j];
    if( x>=0 ){
      testcase( x==BMS-1 );
      testcase( x==BMS-2 );
      if( x<BMS-1 ) m |= MASKBIT(x);
    }






















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/*
** Return True if it is possible that pIndex might be useful in
** implementing the ORDER BY clause in pBuilder.
**
** Return False if pBuilder does not contain an ORDER BY clause or
** if there is no way for pIndex to be useful in implementing that
** ORDER BY clause.
*/
static int indexMightHelpWithOrderBy(
  WhereLoopBuilder *pBuilder,
  Index *pIndex,
  int iCursor
){
  ExprList *pOB;
  int ii, jj;

  if( pIndex->bUnordered ) return 0;
  if( (pOB = pBuilder->pWInfo->pOrderBy)==0 ) return 0;
  for(ii=0; ii<pOB->nExpr; ii++){
    Expr *pExpr = sqlite3ExprSkipCollate(pOB->a[ii].pExpr);
    if( pExpr->op!=TK_COLUMN ) return 0;
    if( pExpr->iTable==iCursor ){
      if( pExpr->iColumn<0 ) return 1;
      for(jj=0; jj<pIndex->nKeyCol; jj++){
        if( pExpr->iColumn==pIndex->aiColumn[jj] ) return 1;
      }
    }
  }
  return 0;
}

/*
** Return a bitmask where 1s indicate that the corresponding column of
** the table is used by an index.  Only the first 63 columns are considered.
*/
static Bitmask columnsInIndex(Index *pIdx){
  Bitmask m = 0;
  int j;
  for(j=pIdx->nColumn-1; j>=0; j--){
    int x = pIdx->aiColumn[j];
    if( x>=0 ){
      testcase( x==BMS-1 );
      testcase( x==BMS-2 );
      if( x<BMS-1 ) m |= MASKBIT(x);
    }

Changes to test/orderby1.test.

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  EXPLAIN QUERY PLAN SELECT 5 UNION ALL SELECT 3 ORDER BY 1
} {~/B-TREE/}
do_execsql_test 5.2 {
  SELECT 5 UNION ALL SELECT 3 ORDER BY 1
} {3 5}

# The following test (originally derived from a single test within fuzz.test)
# verifies that a PseudoTable cursor is not closed prematurely in a deeply
# nested query.  This test caused a segfault on 3.8.5 beta.
#
do_execsql_test 6.0 {
  CREATE TABLE abc(a, b, c);
  INSERT INTO abc VALUES(1, 2, 3);
  INSERT INTO abc VALUES(4, 5, 6);
  INSERT INTO abc VALUES(7, 8, 9);
  SELECT (
    SELECT 'hardware' FROM ( 
      SELECT 'software' ORDER BY 'firmware' ASC, 'sportswear' DESC 
    ) GROUP BY 1 HAVING length(b)
  )
  FROM abc;
} {hardware hardware hardware}
















finish_test






















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  EXPLAIN QUERY PLAN SELECT 5 UNION ALL SELECT 3 ORDER BY 1
} {~/B-TREE/}
do_execsql_test 5.2 {
  SELECT 5 UNION ALL SELECT 3 ORDER BY 1
} {3 5}

# The following test (originally derived from a single test within fuzz.test)
# verifies that a PseudoTable cursor is not closed prematurely in a deeply
# nested query.  This test caused a segfault on 3.8.5 beta.
#
do_execsql_test 6.0 {
  CREATE TABLE abc(a, b, c);
  INSERT INTO abc VALUES(1, 2, 3);
  INSERT INTO abc VALUES(4, 5, 6);
  INSERT INTO abc VALUES(7, 8, 9);
  SELECT (
    SELECT 'hardware' FROM ( 
      SELECT 'software' ORDER BY 'firmware' ASC, 'sportswear' DESC 
    ) GROUP BY 1 HAVING length(b)
  )
  FROM abc;
} {hardware hardware hardware}

# Here is a test for a query-planner problem reported on the SQLite
# mailing list on 2014-09-18 by "Merike".  Beginning with version 3.8.0,
# a separate sort was being used rather than using the single-column
# index.  This was due to an oversight in the indexMightHelpWithOrderby()
# routine in where.c.
#
do_execsql_test 7.0 {
  CREATE TABLE t7(a,b);
  CREATE INDEX t7a ON t7(a);
  CREATE INDEX t7ab ON t7(a,b);
  EXPLAIN QUERY PLAN
  SELECT * FROM t7 WHERE a=?1 ORDER BY rowid;
} {~/ORDER BY/}


finish_test