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Suppress subquery pullup/pushdown when a subquery contains volatile

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functions in its targetlist, to avoid introducing multiple evaluations
of volatile functions that textually appear only once.  This is a
slightly tighter version of Jaime Casanova's recent patch.
This commit is contained in:
Tom Lane
2006-08-19 02:48:53 +00:00
parent 9bf760f7de
commit fb9e56eea1
2 changed files with 22 additions and 2 deletions
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13
src/backend/optimizer/path/allpaths.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.151 2006/08/10 02:36:28 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.152 2006/08/19 02:48:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -871,6 +871,10 @@ compare_tlist_datatypes(List *tlist, List *colTypes,
* 5. We must not push down any quals that refer to subselect outputs that
* return sets, else we'd introduce functions-returning-sets into the
* subquery's WHERE/HAVING quals.
*
* 6. We must not push down any quals that refer to subselect outputs that
* contain volatile functions, for fear of introducing strange results due
* to multiple evaluation of a volatile function.
*/
static bool
qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
@ -940,6 +944,13 @@ qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
safe = false;
break;
}
/* Refuse volatile functions (point 6) */
if (contain_volatile_functions((Node *) tle->expr))
{
safe = false;
break;
}
}
list_free(vars);

11
src/backend/optimizer/prep/prepjointree.c
View File

@ -15,7 +15,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.42 2006/08/12 20:05:55 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.43 2006/08/19 02:48:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -656,6 +656,15 @@ is_simple_subquery(Query *subquery)
if (expression_returns_set((Node *) subquery->targetList))
return false;
/*
* Don't pull up a subquery that has any volatile functions in its
* targetlist. Otherwise we might introduce multiple evaluations of
* these functions, if they get copied to multiple places in the upper
* query, leading to surprising results.
*/
if (contain_volatile_functions((Node *) subquery->targetList))
return false;
/*
* Hack: don't try to pull up a subquery with an empty jointree.
* query_planner() will correctly generate a Result plan for a jointree