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Commit1879175

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Fix performance bug in constant-expression simplifier. After finding
that the inputs to a given operator can be recursively simplified toconstants, it was evaluating the operator using the op's *original*(unsimplified) arg list, so that any subexpressions had to be evaluatedagain. A constant subexpression at depth N got evaluated N times.Probably not very important in practical situations, but it made us lookreal slow in MySQL's 'crashme' test...
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‎src/backend/optimizer/util/clauses.c

Lines changed: 13 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.60 2000/02/20 21:32:06 tgl Exp $
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* $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.61 2000/03/12 19:32:06 tgl Exp $
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*
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* HISTORY
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* AUTHORDATEMAJOR EVENT
@@ -991,18 +991,26 @@ eval_const_expressions_mutator (Node *node, void *context)
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* duplication of code and ensure we get the same result
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* as the executor would get.
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*
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* The only setup needed here is the replace_opid()
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* that we already did for the OP_EXPR case.
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*
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* Build a new Expr node containing the already-simplified
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* arguments. The only other setup needed here is the
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* replace_opid() that we already did for the OP_EXPR case.
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*/
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newexpr=makeNode(Expr);
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newexpr->typeOid=expr->typeOid;
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newexpr->opType=expr->opType;
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newexpr->oper=expr->oper;
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newexpr->args=args;
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/*
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* It is OK to pass econtext = NULL because none of the
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* ExecEvalExpr() code used in this situation will use
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* econtext. That might seem fortuitous, but it's not
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* so unreasonable --- a constant expression does not
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* depend on context, by definition, n'est ce pas?
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*/
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const_val=ExecEvalExpr((Node*)expr,NULL,
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const_val=ExecEvalExpr((Node*)newexpr,NULL,
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&const_is_null,&isDone);
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Assert(isDone);/* if this isn't set, we blew it... */
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pfree(newexpr);
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/*
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* Make the constant result node.
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*/

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