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Commit0cf1668

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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 parent4ee4594 commit0cf1668

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5 files changed

+76
-9
lines changed

5 files changed

+76
-9
lines changed

‎src/backend/optimizer/path/allpaths.c‎

Lines changed: 16 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1011,10 +1011,15 @@ get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
10111011
* accumulate_append_subpath
10121012
*Add a subpath to the list being built for an Append or MergeAppend
10131013
*
1014-
* It's possible that the child is itself an Append path, in which case
1015-
* we can "cut out the middleman" and just add its child paths to our
1016-
* own list. (We don't try to do this earlier because we need to
1017-
* apply both levels of transformation to the quals.)
1014+
* It's possible that the child is itself an Append or MergeAppend path, in
1015+
* which case we can "cut out the middleman" and just add its child paths to
1016+
* our own list. (We don't try to do this earlier because we need to apply
1017+
* both levels of transformation to the quals.)
1018+
*
1019+
* Note that if we omit a child MergeAppend in this way, we are effectively
1020+
* omitting a sort step, which seems fine: if the parent is to be an Append,
1021+
* its result would be unsorted anyway, while if the parent is to be a
1022+
* MergeAppend, there's no point in a separate sort on a child.
10181023
*/
10191024
staticList*
10201025
accumulate_append_subpath(List*subpaths,Path*path)
@@ -1026,6 +1031,13 @@ accumulate_append_subpath(List *subpaths, Path *path)
10261031
/* list_copy is important here to avoid sharing list substructure */
10271032
returnlist_concat(subpaths,list_copy(apath->subpaths));
10281033
}
1034+
elseif (IsA(path,MergeAppendPath))
1035+
{
1036+
MergeAppendPath*mpath= (MergeAppendPath*)path;
1037+
1038+
/* list_copy is important here to avoid sharing list substructure */
1039+
returnlist_concat(subpaths,list_copy(mpath->subpaths));
1040+
}
10291041
else
10301042
returnlappend(subpaths,path);
10311043
}

‎src/backend/optimizer/path/equivclass.c‎

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1937,16 +1937,20 @@ add_child_rel_equivalences(PlannerInfo *root,
19371937
if (cur_ec->ec_has_volatile)
19381938
continue;
19391939

1940-
/* No point in searching if parent rel not mentioned in eclass */
1941-
if (!bms_is_subset(parent_rel->relids,cur_ec->ec_relids))
1940+
/*
1941+
* No point in searching if parent rel not mentioned in eclass; but
1942+
* we can't tell that for sure if parent rel is itself a child.
1943+
*/
1944+
if (parent_rel->reloptkind==RELOPT_BASEREL&&
1945+
!bms_is_subset(parent_rel->relids,cur_ec->ec_relids))
19421946
continue;
19431947

19441948
foreach(lc2,cur_ec->ec_members)
19451949
{
19461950
EquivalenceMember*cur_em= (EquivalenceMember*)lfirst(lc2);
19471951

1948-
if (cur_em->em_is_const||cur_em->em_is_child)
1949-
continue;/* ignore constsand childrenhere */
1952+
if (cur_em->em_is_const)
1953+
continue;/* ignore consts here */
19501954

19511955
/* Does it reference parent_rel? */
19521956
if (bms_overlap(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
@@ -731,7 +731,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
731731

732732
/* Compute sort column info, and adjust MergeAppend's tlist as needed */
733733
(void)prepare_sort_from_pathkeys(root,plan,pathkeys,
734-
NULL,
734+
best_path->path.parent->relids,
735735
NULL,
736736
true,
737737
&node->numCols,

‎src/test/regress/expected/union.out‎

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -500,9 +500,39 @@ 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+
set enable_indexonlyscan = off;
511+
create table events (event_id int primary key);
512+
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "events_pkey" for table "events"
513+
create table other_events (event_id int primary key);
514+
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "other_events_pkey" for table "other_events"
515+
create table events_child () inherits (events);
516+
explain (costs off)
517+
select event_id
518+
from (select event_id from events
519+
union all
520+
select event_id from other_events) ss
521+
order by event_id;
522+
QUERY PLAN
523+
----------------------------------------------------------------
524+
Result
525+
-> Merge Append
526+
Sort Key: public.events.event_id
527+
-> Index Scan using events_pkey on events
528+
-> Sort
529+
Sort Key: public.events.event_id
530+
-> Seq Scan on events_child events
531+
-> Index Scan using other_events_pkey on other_events
532+
(8 rows)
533+
534+
drop table events_child, events, other_events;
535+
reset enable_indexonlyscan;
506536
-- Test constraint exclusion of UNION ALL subqueries
507537
explain (costs off)
508538
SELECT * FROM

‎src/test/regress/sql/union.sql‎

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -196,9 +196,30 @@ 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;
207+
set enable_indexonlyscan= off;
208+
209+
createtableevents (event_idintprimary key);
210+
createtableother_events (event_idintprimary key);
211+
createtableevents_child () inherits (events);
212+
213+
explain (costs off)
214+
select event_id
215+
from (select event_idfrom events
216+
union all
217+
select event_idfrom other_events) ss
218+
order by event_id;
219+
220+
droptable events_child, events, other_events;
221+
222+
reset enable_indexonlyscan;
202223

203224
-- Test constraint exclusion of UNION ALL subqueries
204225
explain (costs off)

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