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Improve planner estimates for size of tuple hash tables.

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This commit is contained in:
Tom Lane
2006-06-28 20:04:38 +00:00
parent 485375a1c9
commit 1c1ecd5124
2 changed files with 8 additions and 6 deletions
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10
src/backend/optimizer/plan/subselect.c
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/plan/subselect.c,v 1.107 2006/05/03 00:24:56 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/plan/subselect.c,v 1.108 2006/06/28 20:04:38 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -585,11 +585,13 @@ subplan_is_hashable(SubLink *slink, SubPlan *node)
return false;
/*
* The estimated size of the subquery result must fit in work_mem. (XXX
* what about hashtable overhead?)
* The estimated size of the subquery result must fit in work_mem.
* (Note: we use sizeof(HeapTupleHeaderData) here even though the tuples
* will actually be stored as MinimalTuples; this provides some fudge
* factor for hashtable overhead.)
*/
subquery_size = node->plan->plan_rows *
(MAXALIGN(node->plan->plan_width) + MAXALIGN(sizeof(HeapTupleData)));
(MAXALIGN(node->plan->plan_width) + MAXALIGN(sizeof(HeapTupleHeaderData)));
if (subquery_size > work_mem * 1024L)
return false;