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Commitc8f81df

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Skip eval_const_expressions when the query is such that the expression
would be evaluated only once anyway (ie, it's just a SELECT with noFROM or an INSERT ... VALUES). The planner can't do it any faster thanthe executor, so no point in an extra copying of the expression tree.
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‎src/backend/optimizer/plan/planner.c

Lines changed: 21 additions & 2 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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* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.186 2005/05/22 22:30:19 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.187 2005/05/30 01:04:44 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -385,6 +385,14 @@ subquery_planner(Query *parse, double tuple_fraction)
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staticNode*
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preprocess_expression(Query*parse,Node*expr,intkind)
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{
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/*
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* Fall out quickly if expression is empty. This occurs often enough
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* to be worth checking. Note that null->null is the correct conversion
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* for implicit-AND result format, too.
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*/
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if (expr==NULL)
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returnNULL;
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/*
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* If the query has any join RTEs, replace join alias variables with
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* base-relation variables. We must do this before sublink processing,
@@ -401,8 +409,19 @@ preprocess_expression(Query *parse, Node *expr, int kind)
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* form. All processing of a qual expression after this point must be
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* careful to maintain AND/OR flatness --- that is, do not generate a tree
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* with AND directly under AND, nor OR directly under OR.
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*
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* Because this is a relatively expensive process, we skip it when the
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* query is trivial, such as "SELECT 2+2;" or "INSERT ... VALUES()".
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* The expression will only be evaluated once anyway, so no point in
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* pre-simplifying; we can't execute it any faster than the executor can,
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* and we will waste cycles copying the tree. Notice however that we
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* still must do it for quals (to get AND/OR flatness); and if we are
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* in a subquery we should not assume it will be done only once.
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*/
405-
expr=eval_const_expressions(expr);
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if (parse->jointree->fromlist!=NIL||
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kind==EXPRKIND_QUAL||
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PlannerQueryLevel>1)
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expr=eval_const_expressions(expr);
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/*
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* If it's a qual or havingQual, canonicalize it.

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