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Commit555d0b2

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committed
Back-patch "Fix EquivalenceClass processing for nested append relations".
When we committeda87c729, we somehowfailed to notice that it didn't merely improve plan quality for expressionindexes; there were very closely related cases that failed outright with"could not find pathkey item to sort". The failing cases seem to be thosewhere the planner was already capable of selecting a MergeAppend plan,and there was inheritance involved: the lack of appropriate eclass childmembers would prevent prepare_sort_from_pathkeys() from succeeding on theMergeAppend's child plan nodes for inheritance child tables.Accordingly, back-patch into 9.1 through 9.3, along with an extraregression test case covering the problem.Per trouble report from Michael Glaesemann.
1 parent8658680 commit555d0b2

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5 files changed

+71
-9
lines changed

5 files changed

+71
-9
lines changed

‎src/backend/optimizer/path/allpaths.c

Lines changed: 16 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -635,10 +635,15 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
635635
* accumulate_append_subpath
636636
*Add a subpath to the list being built for an Append or MergeAppend
637637
*
638-
* It's possible that the child is itself an Append path, in which case
639-
* we can "cut out the middleman" and just add its child paths to our
640-
* own list. (We don't try to do this earlier because we need to
641-
* apply both levels of transformation to the quals.)
638+
* It's possible that the child is itself an Append or MergeAppend path, in
639+
* which case we can "cut out the middleman" and just add its child paths to
640+
* our own list. (We don't try to do this earlier because we need to apply
641+
* both levels of transformation to the quals.)
642+
*
643+
* Note that if we omit a child MergeAppend in this way, we are effectively
644+
* omitting a sort step, which seems fine: if the parent is to be an Append,
645+
* its result would be unsorted anyway, while if the parent is to be a
646+
* MergeAppend, there's no point in a separate sort on a child.
642647
*/
643648
staticList*
644649
accumulate_append_subpath(List*subpaths,Path*path)
@@ -650,6 +655,13 @@ accumulate_append_subpath(List *subpaths, Path *path)
650655
/* list_copy is important here to avoid sharing list substructure */
651656
returnlist_concat(subpaths,list_copy(apath->subpaths));
652657
}
658+
elseif (IsA(path,MergeAppendPath))
659+
{
660+
MergeAppendPath*mpath= (MergeAppendPath*)path;
661+
662+
/* list_copy is important here to avoid sharing list substructure */
663+
returnlist_concat(subpaths,list_copy(mpath->subpaths));
664+
}
653665
else
654666
returnlappend(subpaths,path);
655667
}

‎src/backend/optimizer/path/equivclass.c

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1850,16 +1850,20 @@ add_child_rel_equivalences(PlannerInfo *root,
18501850
if (cur_ec->ec_has_volatile)
18511851
continue;
18521852

1853-
/* No point in searching if parent rel not mentioned in eclass */
1854-
if (!bms_is_subset(parent_rel->relids,cur_ec->ec_relids))
1853+
/*
1854+
* No point in searching if parent rel not mentioned in eclass; but
1855+
* we can't tell that for sure if parent rel is itself a child.
1856+
*/
1857+
if (parent_rel->reloptkind==RELOPT_BASEREL&&
1858+
!bms_is_subset(parent_rel->relids,cur_ec->ec_relids))
18551859
continue;
18561860

18571861
foreach(lc2,cur_ec->ec_members)
18581862
{
18591863
EquivalenceMember*cur_em= (EquivalenceMember*)lfirst(lc2);
18601864

1861-
if (cur_em->em_is_child)
1862-
continue;/* ignorechildren here */
1865+
if (cur_em->em_is_const)
1866+
continue;/* ignoreconsts here */
18631867

18641868
/* Does it reference (only) parent_rel? */
18651869
if (bms_equal(cur_em->em_relids,parent_rel->relids))

‎src/backend/optimizer/plan/createplan.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -700,7 +700,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
700700

701701
/* Compute sort column info, and adjust MergeAppend's tlist as needed */
702702
(void)prepare_sort_from_pathkeys(root,plan,pathkeys,
703-
NULL,
703+
best_path->path.parent->relids,
704704
NULL,
705705
true,
706706
&node->numCols,

‎src/test/regress/expected/union.out

Lines changed: 28 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -500,9 +500,37 @@ explain (costs off)
500500
Index Cond: (ab = 'ab'::text)
501501
(6 rows)
502502

503+
--
504+
-- Test that ORDER BY for UNION ALL can be pushed down to inheritance
505+
-- children.
506+
--
503507
reset enable_seqscan;
504508
reset enable_indexscan;
505509
reset enable_bitmapscan;
510+
create table events (event_id int primary key);
511+
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "events_pkey" for table "events"
512+
create table other_events (event_id int primary key);
513+
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "other_events_pkey" for table "other_events"
514+
create table events_child () inherits (events);
515+
explain (costs off)
516+
select event_id
517+
from (select event_id from events
518+
union all
519+
select event_id from other_events) ss
520+
order by event_id;
521+
QUERY PLAN
522+
----------------------------------------------------------------
523+
Result
524+
-> Merge Append
525+
Sort Key: public.events.event_id
526+
-> Index Scan using events_pkey on events
527+
-> Sort
528+
Sort Key: public.events.event_id
529+
-> Seq Scan on events_child events
530+
-> Index Scan using other_events_pkey on other_events
531+
(8 rows)
532+
533+
drop table events_child, events, other_events;
506534
-- Test constraint exclusion of UNION ALL subqueries
507535
explain (costs off)
508536
SELECT * FROM

‎src/test/regress/sql/union.sql

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -196,10 +196,28 @@ explain (costs off)
196196
SELECT*FROM t2) t
197197
WHERE ab='ab';
198198

199+
--
200+
-- Test that ORDER BY for UNION ALL can be pushed down to inheritance
201+
-- children.
202+
--
203+
199204
reset enable_seqscan;
200205
reset enable_indexscan;
201206
reset enable_bitmapscan;
202207

208+
createtableevents (event_idintprimary key);
209+
createtableother_events (event_idintprimary key);
210+
createtableevents_child () inherits (events);
211+
212+
explain (costs off)
213+
select event_id
214+
from (select event_idfrom events
215+
union all
216+
select event_idfrom other_events) ss
217+
order by event_id;
218+
219+
droptable events_child, events, other_events;
220+
203221
-- Test constraint exclusion of UNION ALL subqueries
204222
explain (costs off)
205223
SELECT*FROM

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