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Commit6217a8c

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Fix some bogosities in the code that deals with estimating the fraction
of tuples we are going to retrieve from a sub-SELECT. Must have beenhalf asleep when I did this code the first time :-(
1 parenta164208 commit6217a8c

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3 files changed

+42
-29
lines changed

3 files changed

+42
-29
lines changed

‎src/backend/optimizer/path/costsize.c

Lines changed: 11 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -42,7 +42,7 @@
4242
* Portions Copyright (c) 1994, Regents of the University of California
4343
*
4444
* IDENTIFICATION
45-
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.52 2000/02/15 20:49:16 tgl Exp $
45+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.53 2000/03/14 02:23:14 tgl Exp $
4646
*
4747
*-------------------------------------------------------------------------
4848
*/
@@ -687,8 +687,8 @@ cost_qual_eval_walker(Node *node, Cost *total)
687687
* (We assume that sub-selects that can be executed as
688688
* InitPlans have already been removed from the expression.)
689689
*
690-
* NOTE: this logic should agree withmake_subplan in
691-
* subselect.c.
690+
* NOTE: this logic should agree withthe estimates used by
691+
*make_subplan() in plan/subselect.c.
692692
*/
693693
{
694694
SubPlan*subplan= (SubPlan*)expr->oper;
@@ -701,16 +701,18 @@ cost_qual_eval_walker(Node *node, Cost *total)
701701
subcost=plan->startup_cost+
702702
(plan->total_cost-plan->startup_cost) /plan->plan_rows;
703703
}
704-
elseif (subplan->sublink->subLinkType==EXPR_SUBLINK)
705-
{
706-
/* assume we need all tuples */
707-
subcost=plan->total_cost;
708-
}
709-
else
704+
elseif (subplan->sublink->subLinkType==ALL_SUBLINK||
705+
subplan->sublink->subLinkType==ANY_SUBLINK)
710706
{
711707
/* assume we need 50% of the tuples */
712708
subcost=plan->startup_cost+
713709
0.50* (plan->total_cost-plan->startup_cost);
710+
/* XXX what if subplan has been materialized? */
711+
}
712+
else
713+
{
714+
/* assume we need all tuples */
715+
subcost=plan->total_cost;
714716
}
715717
*total+=subcost;
716718
}

‎src/backend/optimizer/plan/planner.c

Lines changed: 10 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.76 2000/02/21 01:13:04 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.77 2000/03/14 02:23:15 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -360,11 +360,14 @@ union_planner(Query *parse,
360360
* In GROUP BY mode, we have the little problem that we don't
361361
* really know how many input tuples will be needed to make a
362362
* group, so we can't translate an output LIMIT count into an
363-
* input count. For lack of a better idea, assume10% of the
363+
* input count. For lack of a better idea, assume25% of the
364364
* input data will be processed if there is any output limit.
365+
* However, if the caller gave us a fraction rather than an
366+
* absolute count, we can keep using that fraction (which amounts
367+
* to assuming that all the groups are about the same size).
365368
*/
366-
if (tuple_fraction>0.0)
367-
tuple_fraction=0.10;
369+
if (tuple_fraction >=1.0)
370+
tuple_fraction=0.25;
368371
/*
369372
* If both GROUP BY and ORDER BY are specified, we will need
370373
* two levels of sort --- and, therefore, certainly need to
@@ -386,11 +389,10 @@ union_planner(Query *parse,
386389
{
387390
/*
388391
* SELECT DISTINCT, like GROUP, will absorb an unpredictable
389-
* number of input tuples per output tuple. So, fall back to
390-
* our same old 10% default...
392+
* number of input tuples per output tuple. Handle the same way.
391393
*/
392-
if (tuple_fraction>0.0)
393-
tuple_fraction=0.10;
394+
if (tuple_fraction >=1.0)
395+
tuple_fraction=0.25;
394396
}
395397

396398
/* Generate the (sub) plan */

‎src/backend/optimizer/plan/subselect.c

Lines changed: 21 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
99
* IDENTIFICATION
10-
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.30 2000/03/1123:53:41 tgl Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.31 2000/03/14 02:23:15 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -134,25 +134,34 @@ make_subplan(SubLink *slink)
134134

135135
PlannerInitPlan=NULL;
136136

137-
PlannerQueryLevel++;/* webecomes child */
137+
PlannerQueryLevel++;/* webecome child */
138138

139139
/*
140140
* For an EXISTS subplan, tell lower-level planner to expect that
141-
* only the first tuple will be retrieved. For ALL, ANY,andMULTIEXPR
142-
*subplans,we will be able to stop evaluating if the test condition
143-
*fails,so very often not all the tuples will be retrieved; for lack
144-
*of abetter idea, specify 50% retrieval. ForEXPR_SUBLINK use default
145-
* behavior.
141+
* only the first tuple will be retrieved. For ALLandANY subplans,
142+
* we will be able to stop evaluating if the test condition fails,
143+
* so very often not all the tuples will be retrieved; for lack of a
144+
* better idea, specify 50% retrieval. ForEXPR and MULTIEXPR subplans,
145+
*use defaultbehavior (we're only expecting one row out, anyway).
146146
*
147-
* NOTE: if you change these numbers, also change cost_qual_eval_walker
148-
* in costsize.c.
147+
* NOTE: if you change these numbers, also change cost_qual_eval_walker()
148+
* in path/costsize.c.
149+
*
150+
* XXX If an ALL/ANY subplan is uncorrelated, we may decide to materialize
151+
* its result below. In that case it would've been better to specify
152+
* full retrieval. At present, however, we can only detect correlation
153+
* or lack of it after we've made the subplan :-(. Perhaps detection
154+
* of correlation should be done as a separate step. Meanwhile, we don't
155+
* want to be too optimistic about the percentage of tuples retrieved,
156+
* for fear of selecting a plan that's bad for the materialization case.
149157
*/
150158
if (slink->subLinkType==EXISTS_SUBLINK)
151159
tuple_fraction=1.0;/* just like a LIMIT 1 */
152-
elseif (slink->subLinkType==EXPR_SUBLINK)
153-
tuple_fraction=-1.0;/* default behavior */
154-
else
160+
elseif (slink->subLinkType==ALL_SUBLINK||
161+
slink->subLinkType==ANY_SUBLINK)
155162
tuple_fraction=0.5;/* 50% */
163+
else
164+
tuple_fraction=-1.0;/* default behavior */
156165

157166
node->plan=plan=union_planner(subquery,tuple_fraction);
158167

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