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Overview
Comment:Avoid generating hints using constraints that are also used to initialize the cursor, since presumably the cursor already knows about those constraints.
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SHA1: 142b048ac778620dd4e448c2e969982eb8188501
User & Date: drh 2015-08-17 17:19:28
Context
2015-08-18
15:58
Provide hints for all terms in a range constraint if there are any equality terms anywhere in the constraint. Range constraint terms are only omitted for a pure range constraint with no equality prefix. (check-in: b5897bc0 user: drh tags: cursor-hints)
2015-08-17
17:19
Avoid generating hints using constraints that are also used to initialize the cursor, since presumably the cursor already knows about those constraints. (check-in: 142b048a user: drh tags: cursor-hints)
2015-08-15
00:51
Change the display of the P4 operand of CursorHint in EXPLAIN output to function notation. (check-in: bee73d42 user: drh tags: cursor-hints)
Changes
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Changes to src/wherecode.c. 

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  return rc;
}

/*
** Insert an OP_CursorHint instruction if it is appropriate to do so.
*/
static void codeCursorHint(
  WhereInfo *pWInfo,
  WhereLevel *pLevel

){
  Parse *pParse = pWInfo->pParse;
  sqlite3 *db = pParse->db;
  Vdbe *v = pParse->pVdbe;
  Expr *pExpr = 0;
  WhereLoop *pLoop = pLevel->pWLoop;
  int iCur;
  WhereClause *pWC;
  WhereTerm *pTerm;

  int i;
  struct CCurHint sHint;
  Walker sWalker;

  if( OptimizationDisabled(db, SQLITE_CursorHints) ) return;
  iCur = pLevel->iTabCur;
  assert( iCur==pWInfo->pTabList->a[pLevel->iFrom].iCursor );
  sHint.iTabCur = iCur;
  sHint.iIdxCur = pLevel->iIdxCur;
  sHint.pIdx = pLoop->u.btree.pIndex;
  memset(&sWalker, 0, sizeof(sWalker));
  sWalker.pParse = pParse;
  sWalker.u.pCCurHint = &sHint;
  pWC = &pWInfo->sWC;

  for(i=0; i<pWC->nTerm; i++){
    pTerm = &pWC->a[i];
    if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
    if( pTerm->prereqAll & pLevel->notReady ) continue;
    if( ExprHasProperty(pTerm->pExpr, EP_FromJoin) ) continue;









    if( sqlite3ExprContainsSubquery(pTerm->pExpr) ) continue;



    if( sHint.pIdx!=0 ){
      sWalker.eCode = 0;
      sWalker.xExprCallback = codeCursorHintCheckExpr;
      sqlite3WalkExpr(&sWalker, pTerm->pExpr);
      if( sWalker.eCode ) continue;
    }


    pExpr = sqlite3ExprAnd(db, pExpr, sqlite3ExprDup(db, pTerm->pExpr, 0));
  }
  if( pExpr!=0 ){
    sWalker.xExprCallback = codeCursorHintFixExpr;
    sqlite3WalkExpr(&sWalker, pExpr);
    sqlite3VdbeAddOp4(v, OP_CursorHint, 
                      (sHint.pIdx ? sHint.iIdxCur : sHint.iTabCur), 0, 0,
                      (const char*)pExpr, P4_EXPR);
  }
}
#else
# define codeCursorHint(A,B)  /* No-op */
#endif /* SQLITE_ENABLE_CURSOR_HINTS */

/*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
Bitmask sqlite3WhereCodeOneLoopStart(
................................................................................
    if( pLoop->wsFlags & WHERE_TOP_LIMIT ) pEnd = pLoop->aLTerm[j++];
    assert( pStart!=0 || pEnd!=0 );
    if( bRev ){
      pTerm = pStart;
      pStart = pEnd;
      pEnd = pTerm;
    }
    codeCursorHint(pWInfo, pLevel);
    if( pStart ){
      Expr *pX;             /* The expression that defines the start bound */
      int r1, rTemp;        /* Registers for holding the start boundary */

      /* The following constant maps TK_xx codes into corresponding 
      ** seek opcodes.  It depends on a particular ordering of TK_xx
      */
................................................................................
    testcase( pRangeEnd && (pRangeEnd->eOperator & WO_LE)!=0 );
    testcase( pRangeEnd && (pRangeEnd->eOperator & WO_GE)!=0 );
    startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);
    endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);
    start_constraints = pRangeStart || nEq>0;

    /* Seek the index cursor to the start of the range. */
    codeCursorHint(pWInfo, pLevel);
    nConstraint = nEq;
    if( pRangeStart ){
      Expr *pRight = pRangeStart->pExpr->pRight;
      sqlite3ExprCode(pParse, pRight, regBase+nEq);
      whereLikeOptimizationStringFixup(v, pLevel, pRangeStart);
      if( (pRangeStart->wtFlags & TERM_VNULL)==0
       && sqlite3ExprCanBeNull(pRight)
................................................................................
    static const u8 aStart[] = { OP_Rewind, OP_Last };
    assert( bRev==0 || bRev==1 );
    if( pTabItem->isRecursive ){
      /* Tables marked isRecursive have only a single row that is stored in
      ** a pseudo-cursor.  No need to Rewind or Next such cursors. */
      pLevel->op = OP_Noop;
    }else{
      codeCursorHint(pWInfo, pLevel);
      pLevel->op = aStep[bRev];
      pLevel->p1 = iCur;
      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrBrk);
      VdbeCoverageIf(v, bRev==0);
      VdbeCoverageIf(v, bRev!=0);
      pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
    }








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  return rc;
}

/*
** Insert an OP_CursorHint instruction if it is appropriate to do so.
*/
static void codeCursorHint(
  WhereInfo *pWInfo,    /* The where clause */
  WhereLevel *pLevel,   /* Which loop to provide hints for */
  WhereTerm *pEndRange  /* Hint this end-of-scan boundary term if not NULL */
){
  Parse *pParse = pWInfo->pParse;
  sqlite3 *db = pParse->db;
  Vdbe *v = pParse->pVdbe;
  Expr *pExpr = 0;
  WhereLoop *pLoop = pLevel->pWLoop;
  int iCur;
  WhereClause *pWC;
  WhereTerm *pTerm;
  WhereLoop *pWLoop;
  int i, j;
  struct CCurHint sHint;
  Walker sWalker;

  if( OptimizationDisabled(db, SQLITE_CursorHints) ) return;
  iCur = pLevel->iTabCur;
  assert( iCur==pWInfo->pTabList->a[pLevel->iFrom].iCursor );
  sHint.iTabCur = iCur;
  sHint.iIdxCur = pLevel->iIdxCur;
  sHint.pIdx = pLoop->u.btree.pIndex;
  memset(&sWalker, 0, sizeof(sWalker));
  sWalker.pParse = pParse;
  sWalker.u.pCCurHint = &sHint;
  pWC = &pWInfo->sWC;
  pWLoop = pLevel->pWLoop;
  for(i=0; i<pWC->nTerm; i++){
    pTerm = &pWC->a[i];
    if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
    if( pTerm->prereqAll & pLevel->notReady ) continue;
    if( ExprHasProperty(pTerm->pExpr, EP_FromJoin) ) continue;

    /* All terms in pWLoop->aLTerm[] except pEndRange are used to initialize
    ** the cursor.  No need to hint initialization terms. */
    if( pTerm!=pEndRange ){
      for(j=0; j<pWLoop->nLTerm && pWLoop->aLTerm[j]!=pTerm; j++){}
      if( j<pWLoop->nLTerm ) continue;
    }

    /* No subqueries or non-deterministic functions allowed */
    if( sqlite3ExprContainsSubquery(pTerm->pExpr) ) continue;

    /* For an index scan, make sure referenced columns are actually in
    ** the index. */
    if( sHint.pIdx!=0 ){
      sWalker.eCode = 0;
      sWalker.xExprCallback = codeCursorHintCheckExpr;
      sqlite3WalkExpr(&sWalker, pTerm->pExpr);
      if( sWalker.eCode ) continue;
    }

    /* If we survive all prior tests, that means this term is worth hinting */
    pExpr = sqlite3ExprAnd(db, pExpr, sqlite3ExprDup(db, pTerm->pExpr, 0));
  }
  if( pExpr!=0 ){
    sWalker.xExprCallback = codeCursorHintFixExpr;
    sqlite3WalkExpr(&sWalker, pExpr);
    sqlite3VdbeAddOp4(v, OP_CursorHint, 
                      (sHint.pIdx ? sHint.iIdxCur : sHint.iTabCur), 0, 0,
                      (const char*)pExpr, P4_EXPR);
  }
}
#else
# define codeCursorHint(A,B,C)  /* No-op */
#endif /* SQLITE_ENABLE_CURSOR_HINTS */

/*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
Bitmask sqlite3WhereCodeOneLoopStart(
................................................................................
    if( pLoop->wsFlags & WHERE_TOP_LIMIT ) pEnd = pLoop->aLTerm[j++];
    assert( pStart!=0 || pEnd!=0 );
    if( bRev ){
      pTerm = pStart;
      pStart = pEnd;
      pEnd = pTerm;
    }
    codeCursorHint(pWInfo, pLevel, pEnd);
    if( pStart ){
      Expr *pX;             /* The expression that defines the start bound */
      int r1, rTemp;        /* Registers for holding the start boundary */

      /* The following constant maps TK_xx codes into corresponding 
      ** seek opcodes.  It depends on a particular ordering of TK_xx
      */
................................................................................
    testcase( pRangeEnd && (pRangeEnd->eOperator & WO_LE)!=0 );
    testcase( pRangeEnd && (pRangeEnd->eOperator & WO_GE)!=0 );
    startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);
    endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);
    start_constraints = pRangeStart || nEq>0;

    /* Seek the index cursor to the start of the range. */
    codeCursorHint(pWInfo, pLevel, pRangeEnd);
    nConstraint = nEq;
    if( pRangeStart ){
      Expr *pRight = pRangeStart->pExpr->pRight;
      sqlite3ExprCode(pParse, pRight, regBase+nEq);
      whereLikeOptimizationStringFixup(v, pLevel, pRangeStart);
      if( (pRangeStart->wtFlags & TERM_VNULL)==0
       && sqlite3ExprCanBeNull(pRight)
................................................................................
    static const u8 aStart[] = { OP_Rewind, OP_Last };
    assert( bRev==0 || bRev==1 );
    if( pTabItem->isRecursive ){
      /* Tables marked isRecursive have only a single row that is stored in
      ** a pseudo-cursor.  No need to Rewind or Next such cursors. */
      pLevel->op = OP_Noop;
    }else{
      codeCursorHint(pWInfo, pLevel, 0);
      pLevel->op = aStep[bRev];
      pLevel->p1 = iCur;
      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrBrk);
      VdbeCoverageIf(v, bRev==0);
      VdbeCoverageIf(v, bRev!=0);
      pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
    }

Changes to test/cursorhint.test. 

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  p4_of_opcode db CursorHint {
    SELECT * FROM t3 WHERE a<15 AND b>22 AND id!=98
  }
} {AND(AND(LT(c1,15),GT(c2,22)),NE(c0,98))}

# Indexed queries
#
do_test 4.1 {
  db eval {
    CREATE INDEX t1bc ON t1(b,c);
    CREATE INDEX t2yz ON t2(y,z);
  }
  p4_of_opcode db CursorHint {
    SELECT * FROM t1 WHERE b>11;





  }
} {GT(c0,11)}
do_test 4.2 {
  p5_of_opcode db OpenRead . {
    SELECT * FROM t1 WHERE b>11;
  }
} {02 00}
do_test 4.3 {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b>11;
  }
} {GT(c0,11)}





do_test 4.4 {
  p5_of_opcode db OpenRead . {
    SELECT c FROM t1 WHERE b>11;
  }
} {00}






















finish_test








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  p4_of_opcode db CursorHint {
    SELECT * FROM t3 WHERE a<15 AND b>22 AND id!=98
  }
} {AND(AND(LT(c1,15),GT(c2,22)),NE(c0,98))}

# Indexed queries
#
do_test 4.1asc {
  db eval {
    CREATE INDEX t1bc ON t1(b,c);
    CREATE INDEX t2yz ON t2(y,z);
  }
  p4_of_opcode db CursorHint {
    SELECT * FROM t1 WHERE b>11 ORDER BY b ASC;
  }
} {}
do_test 4.1desc {
  p4_of_opcode db CursorHint {
    SELECT * FROM t1 WHERE b>11 ORDER BY b DESC;
  }
} {GT(c0,11)}
do_test 4.2 {
  p5_of_opcode db OpenRead . {
    SELECT * FROM t1 WHERE b>11;
  }
} {02 00}
do_test 4.3asc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b<11 ORDER BY b ASC;
  }
} {LT(c0,11)}
do_test 4.3desc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b<11 ORDER BY b DESC;
  }
} {}
do_test 4.4 {
  p5_of_opcode db OpenRead . {
    SELECT c FROM t1 WHERE b<11;
  }
} {00}

do_test 4.5asc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b>=10 AND b<=20 ORDER BY b ASC;
  }
} {LE(c0,20)}
do_test 4.5desc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b>=10 AND b<=20 ORDER BY b DESC;
  }
} {GE(c0,10)}
do_test 4.6asc {
  p4_of_opcode db CursorHint {
    SELECT rowid FROM t1 WHERE b=22 AND c>=10 AND c<=20 ORDER BY b,c ASC;
  }
} {LE(c1,20)}
do_test 4.6desc {
  p4_of_opcode db CursorHint {
    SELECT rowid FROM t1 WHERE b=22 AND c>=10 AND c<=20 ORDER BY b,c DESC;
  }
} {GE(c1,10)}

finish_test

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