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Commit491c24f

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Make entirely-dummy appendrels get marked as such in set_append_rel_size.
The planner generally expects that the estimated rowcount of any relationis at least one row, *unless* it has been proven empty by constraintexclusion or similar mechanisms, which is marked by installing a dummy pathas the rel's cheapest path (cf. IS_DUMMY_REL). When I split upallpaths.c's processing of base rels into separate set_base_rel_sizes andset_base_rel_pathlists steps, the intention was that dummy rels would getmarked as such during the "set size" step; this is what justifies an Assertin indxpath.c's get_loop_count that other relations should either be dummyor have positive rowcount. Unfortunately I didn't get that quite rightfor append relations: if all the child rels have been proven empty thenset_append_rel_size would come up with a rowcount of zero, which iscorrect, but it didn't then do set_dummy_rel_pathlist. (We would haveended up with the right state after set_append_rel_pathlist, but that'stoo late, if we generate indexpaths for some other rel first.)In addition to fixing the actual bug, I installed an Assert enforcing thisconvention in set_rel_size; that then allows simplification of a coupleof now-redundant tests for zero rowcount in set_append_rel_size.Also, to cover the possibility that third-party FDWs have been carelessabout not returning a zero rowcount estimate, apply clamp_row_est towhatever an FDW comes up with as the rows estimate.Per report from Andreas Seltenreich. Back-patch to 9.2. Earlier branchesdid not have the separation between set_base_rel_sizes andset_base_rel_pathlists steps, so there was no intermediate state where anappendrel would have had inconsistent rowcount and pathlist. It's possiblethat adding the Assert to set_rel_size would be a good idea in olderbranches too; but since they're not under development any more, it's likelynot worth the trouble.
1 parent41ed5bb commit491c24f

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3 files changed

+93
-42
lines changed

3 files changed

+93
-42
lines changed

‎src/backend/optimizer/path/allpaths.c

Lines changed: 62 additions & 42 deletions
Original file line numberDiff line numberDiff line change
@@ -343,6 +343,11 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
343343
break;
344344
}
345345
}
346+
347+
/*
348+
* We insist that all non-dummy rels have a nonzero rowcount estimate.
349+
*/
350+
Assert(rel->rows>0||IS_DUMMY_REL(rel));
346351
}
347352

348353
/*
@@ -461,6 +466,9 @@ set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
461466

462467
/* Let FDW adjust the size estimates, if it can */
463468
rel->fdwroutine->GetForeignRelSize(root,rel,rte->relid);
469+
470+
/* ... but do not let it set the rows estimate to zero */
471+
rel->rows=clamp_row_est(rel->rows);
464472
}
465473

466474
/*
@@ -493,6 +501,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
493501
Indexrti,RangeTblEntry*rte)
494502
{
495503
intparentRTindex=rti;
504+
boolhas_live_children;
496505
doubleparent_rows;
497506
doubleparent_size;
498507
double*parent_attrsizes;
@@ -513,6 +522,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
513522
* Note: if you consider changing this logic, beware that child rels could
514523
* have zero rows and/or width, if they were excluded by constraints.
515524
*/
525+
has_live_children= false;
516526
parent_rows=0;
517527
parent_size=0;
518528
nattrs=rel->max_attr-rel->min_attr+1;
@@ -640,70 +650,80 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
640650
if (IS_DUMMY_REL(childrel))
641651
continue;
642652

653+
/* We have at least one live child. */
654+
has_live_children= true;
655+
643656
/*
644657
* Accumulate size information from each live child.
645658
*/
646-
if (childrel->rows>0)
659+
Assert(childrel->rows>0);
660+
661+
parent_rows+=childrel->rows;
662+
parent_size+=childrel->width*childrel->rows;
663+
664+
/*
665+
* Accumulate per-column estimates too. We need not do anything for
666+
* PlaceHolderVars in the parent list. If child expression isn't a
667+
* Var, or we didn't record a width estimate for it, we have to fall
668+
* back on a datatype-based estimate.
669+
*
670+
* By construction, child's reltargetlist is 1-to-1 with parent's.
671+
*/
672+
forboth(parentvars,rel->reltargetlist,
673+
childvars,childrel->reltargetlist)
647674
{
648-
parent_rows+=childrel->rows;
649-
parent_size+=childrel->width*childrel->rows;
675+
Var*parentvar= (Var*)lfirst(parentvars);
676+
Node*childvar= (Node*)lfirst(childvars);
650677

651-
/*
652-
* Accumulate per-column estimates too. We need not do anything
653-
* for PlaceHolderVars in the parent list. If child expression
654-
* isn't a Var, or we didn't record a width estimate for it, we
655-
* have to fall back on a datatype-based estimate.
656-
*
657-
* By construction, child's reltargetlist is 1-to-1 with parent's.
658-
*/
659-
forboth(parentvars,rel->reltargetlist,
660-
childvars,childrel->reltargetlist)
678+
if (IsA(parentvar,Var))
661679
{
662-
Var*parentvar= (Var*)lfirst(parentvars);
663-
Node*childvar= (Node*)lfirst(childvars);
680+
intpndx=parentvar->varattno-rel->min_attr;
681+
int32child_width=0;
664682

665-
if (IsA(parentvar,Var))
683+
if (IsA(childvar,Var)&&
684+
((Var*)childvar)->varno==childrel->relid)
666685
{
667-
intpndx=parentvar->varattno-rel->min_attr;
668-
int32child_width=0;
686+
intcndx= ((Var*)childvar)->varattno-childrel->min_attr;
669687

670-
if (IsA(childvar,Var)&&
671-
((Var*)childvar)->varno==childrel->relid)
672-
{
673-
intcndx= ((Var*)childvar)->varattno-childrel->min_attr;
674-
675-
child_width=childrel->attr_widths[cndx];
676-
}
677-
if (child_width <=0)
678-
child_width=get_typavgwidth(exprType(childvar),
679-
exprTypmod(childvar));
680-
Assert(child_width>0);
681-
parent_attrsizes[pndx]+=child_width*childrel->rows;
688+
child_width=childrel->attr_widths[cndx];
682689
}
690+
if (child_width <=0)
691+
child_width=get_typavgwidth(exprType(childvar),
692+
exprTypmod(childvar));
693+
Assert(child_width>0);
694+
parent_attrsizes[pndx]+=child_width*childrel->rows;
683695
}
684696
}
685697
}
686698

687-
/*
688-
* Save the finished size estimates.
689-
*/
690-
rel->rows=parent_rows;
691-
if (parent_rows>0)
699+
if (has_live_children)
692700
{
701+
/*
702+
* Save the finished size estimates.
703+
*/
693704
inti;
694705

706+
Assert(parent_rows>0);
707+
rel->rows=parent_rows;
695708
rel->width=rint(parent_size /parent_rows);
696709
for (i=0;i<nattrs;i++)
697710
rel->attr_widths[i]=rint(parent_attrsizes[i] /parent_rows);
711+
712+
/*
713+
* Set "raw tuples" count equal to "rows" for the appendrel; needed
714+
* because some places assume rel->tuples is valid for any baserel.
715+
*/
716+
rel->tuples=parent_rows;
698717
}
699718
else
700-
rel->width=0;/* attr_widths should be zero already */
701-
702-
/*
703-
* Set "raw tuples" count equal to "rows" for the appendrel; needed
704-
* because some places assume rel->tuples is valid for any baserel.
705-
*/
706-
rel->tuples=parent_rows;
719+
{
720+
/*
721+
* All children were excluded by constraints, so mark the whole
722+
* appendrel dummy. We must do this in this phase so that the rel's
723+
* dummy-ness is visible when we generate paths for other rels.
724+
*/
725+
set_dummy_rel_pathlist(rel);
726+
}
707727

708728
pfree(parent_attrsizes);
709729
}

‎src/test/regress/expected/join.out

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2164,6 +2164,26 @@ select count(*) from tenk1 x where
21642164
(1 row)
21652165

21662166
rollback;
2167+
--
2168+
-- regression test: be sure we cope with proven-dummy append rels
2169+
--
2170+
explain (costs off)
2171+
select aa, bb, unique1, unique1
2172+
from tenk1 right join b on aa = unique1
2173+
where bb < bb and bb is null;
2174+
QUERY PLAN
2175+
--------------------------
2176+
Result
2177+
One-Time Filter: false
2178+
(2 rows)
2179+
2180+
select aa, bb, unique1, unique1
2181+
from tenk1 right join b on aa = unique1
2182+
where bb < bb and bb is null;
2183+
aa | bb | unique1 | unique1
2184+
----+----+---------+---------
2185+
(0 rows)
2186+
21672187
--
21682188
-- Clean up
21692189
--

‎src/test/regress/sql/join.sql

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -353,6 +353,17 @@ select count(*) from tenk1 x where
353353
x.unique1in (selectaa.f1from int4_tbl aa,float8_tbl bbwhereaa.f1=bb.f1);
354354
rollback;
355355

356+
--
357+
-- regression test: be sure we cope with proven-dummy append rels
358+
--
359+
explain (costs off)
360+
select aa, bb, unique1, unique1
361+
from tenk1right join bon aa= unique1
362+
where bb< bband bb isnull;
363+
364+
select aa, bb, unique1, unique1
365+
from tenk1right join bon aa= unique1
366+
where bb< bband bb isnull;
356367

357368
--
358369
-- Clean up

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