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Fix performance bug in constant-expression simplifier. After finding 

that the inputs to a given operator can be recursively simplified to
constants, it was evaluating the operator using the op's *original*
(unsimplified) arg list, so that any subexpressions had to be evaluated
again.  A constant subexpression at depth N got evaluated N times.
Probably not very important in practical situations, but it made us look
real slow in MySQL's 'crashme' test...
This commit is contained in:
Tom Lane 2000-03-12 19:32:06 +00:00
parent ef3386affe
commit 1879175b18
1 changed files with 13 additions and 5 deletions
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18
src/backend/optimizer/util/clauses.c
View File

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