diff options
Diffstat (limited to 'src/backend/optimizer/plan/subselect.c')
| -rw-r--r-- | src/backend/optimizer/plan/subselect.c | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c index da95a2df41f..2790b2740b6 100644 --- a/src/backend/optimizer/plan/subselect.c +++ b/src/backend/optimizer/plan/subselect.c @@ -7,7 +7,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.27 2000/01/26 05:56:38 momjian Exp $ + * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.28 2000/02/15 20:49:18 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -123,6 +123,7 @@ static Node * make_subplan(SubLink *slink) { SubPlan *node = makeNode(SubPlan); + double tuple_fraction; Plan *plan; List *lst; Node *result; @@ -132,7 +133,26 @@ make_subplan(SubLink *slink) PlannerQueryLevel++; /* we becomes child */ - node->plan = plan = union_planner((Query *) slink->subselect); + /* + * For an EXISTS subplan, tell lower-level planner to expect that + * only the first tuple will be retrieved. For ALL, ANY, and MULTIEXPR + * subplans, we will be able to stop evaluating if the test condition + * fails, so very often not all the tuples will be retrieved; for lack + * of a better idea, specify 50% retrieval. For EXPR_SUBLINK use default + * behavior. + * + * NOTE: if you change these numbers, also change cost_qual_eval_walker + * in costsize.c. + */ + if (slink->subLinkType == EXISTS_SUBLINK) + tuple_fraction = 1.0; /* just like a LIMIT 1 */ + else if (slink->subLinkType == EXPR_SUBLINK) + tuple_fraction = -1.0; /* default behavior */ + else + tuple_fraction = 0.5; /* 50% */ + + node->plan = plan = union_planner((Query *) slink->subselect, + tuple_fraction); /* * Assign subPlan, extParam and locParam to plan nodes. At the moment, |