Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commitebb7ae8

Browse files
committed
Fix get_useful_pathkeys_for_relation for volatile expressions
When considering Incremental Sort below a Gather Merge, we need to bea bit more careful when matching pathkeys to EC members. It's not enoughto find a member whose Vars are all in the current relation's target;volatile expressions in particular need to be contained in the target,otherwise it's too early to use the pathkey.Reported-by: Jaime CasanovaAuthor: James ColemanReviewed-by: Tomas VondraBackpatch-through: 13, where the incremental sort code was addedDiscussion:https://postgr.es/m/CAJGNTeNaxpXgBVcRhJX%2B2vSbq%2BF2kJqGBcvompmpvXb7pq%2BoFA%40mail.gmail.com
1 parent92f8718 commitebb7ae8

File tree

5 files changed

+207
-6
lines changed

5 files changed

+207
-6
lines changed

‎src/backend/optimizer/path/allpaths.c

Lines changed: 7 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -2816,7 +2816,8 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
28162816
/*
28172817
* Considering query_pathkeys is always worth it, because it might allow
28182818
* us to avoid a total sort when we have a partially presorted path
2819-
* available.
2819+
* available or to push the total sort into the parallel portion of the
2820+
* query.
28202821
*/
28212822
if (root->query_pathkeys)
28222823
{
@@ -2829,17 +2830,17 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
28292830
EquivalenceClass*pathkey_ec=pathkey->pk_eclass;
28302831

28312832
/*
2832-
* We can only buildan Incremental Sortfor pathkeys which
2833-
*contain an ECmember in the current relation, so ignore any
2834-
*suffixof the list as soon as we find a pathkey without an EC
2835-
*member the relation.
2833+
* We can only builda sortfor pathkeys which contain an EC
2834+
* member in the current relation's target, so ignore any suffix
2835+
* of the list as soon as we find a pathkey without an EC member
2836+
*in the relation.
28362837
*
28372838
* By still returning the prefix of the pathkeys list that does
28382839
* meet criteria of EC membership in the current relation, we
28392840
* enable not just an incremental sort on the entirety of
28402841
* query_pathkeys but also incremental sort below a JOIN.
28412842
*/
2842-
if (!find_em_expr_for_rel(pathkey_ec,rel))
2843+
if (!find_em_expr_usable_for_sorting_rel(pathkey_ec,rel))
28432844
break;
28442845

28452846
npathkeys++;

‎src/backend/optimizer/path/equivclass.c

Lines changed: 70 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -797,6 +797,76 @@ find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel)
797797
returnNULL;
798798
}
799799

800+
/*
801+
* Find an equivalence class member expression that can be safely used by a
802+
* sort node on top of the provided relation. The rules here must match those
803+
* applied in prepare_sort_from_pathkeys.
804+
*/
805+
Expr*
806+
find_em_expr_usable_for_sorting_rel(EquivalenceClass*ec,RelOptInfo*rel)
807+
{
808+
ListCell*lc_em;
809+
810+
/*
811+
* If there is more than one equivalence member matching these
812+
* requirements we'll be content to choose any one of them.
813+
*/
814+
foreach(lc_em,ec->ec_members)
815+
{
816+
EquivalenceMember*em=lfirst(lc_em);
817+
Expr*em_expr=em->em_expr;
818+
PathTarget*target=rel->reltarget;
819+
ListCell*lc_target_expr;
820+
821+
/*
822+
* We shouldn't be trying to sort by an equivalence class that
823+
* contains a constant, so no need to consider such cases any further.
824+
*/
825+
if (em->em_is_const)
826+
continue;
827+
828+
/*
829+
* Any Vars in the equivalence class member need to come from this
830+
* relation. This is a superset of prepare_sort_from_pathkeys ignoring
831+
* child members unless they belong to the rel being sorted.
832+
*/
833+
if (!bms_is_subset(em->em_relids,rel->relids))
834+
continue;
835+
836+
/*
837+
* As long as the expression isn't volatile then
838+
* prepare_sort_from_pathkeys is able to generate a new target entry,
839+
* so there's no need to verify that one already exists.
840+
*/
841+
if (!ec->ec_has_volatile)
842+
returnem->em_expr;
843+
844+
/*
845+
* If, however, it's volatile, we have to verify that the
846+
* equivalence member's expr is already generated in the
847+
* relation's target (we do strip relabels first from both
848+
* expressions, which is cheap and might allow us to match
849+
* more expressions).
850+
*/
851+
while (em_expr&&IsA(em_expr,RelabelType))
852+
em_expr= ((RelabelType*)em_expr)->arg;
853+
854+
foreach(lc_target_expr,target->exprs)
855+
{
856+
Expr*target_expr=lfirst(lc_target_expr);
857+
858+
while (target_expr&&IsA(target_expr,RelabelType))
859+
target_expr= ((RelabelType*)target_expr)->arg;
860+
861+
if (equal(target_expr,em_expr))
862+
returnem->em_expr;
863+
}
864+
}
865+
866+
/* We didn't find any suitable equivalence class expression */
867+
returnNULL;
868+
}
869+
800870
/*
801871
* generate_base_implied_equalities
802872
* Generate any restriction clauses that we can deduce from equivalence

‎src/include/optimizer/paths.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -135,6 +135,7 @@ extern EquivalenceClass *get_eclass_for_sort_expr(PlannerInfo *root,
135135
Relidsrel,
136136
boolcreate_it);
137137
externExpr*find_em_expr_for_rel(EquivalenceClass*ec,RelOptInfo*rel);
138+
externExpr*find_em_expr_usable_for_sorting_rel(EquivalenceClass*ec,RelOptInfo*rel);
138139
externvoidgenerate_base_implied_equalities(PlannerInfo*root);
139140
externList*generate_join_implied_equalities(PlannerInfo*root,
140141
Relidsjoin_relids,

‎src/test/regress/expected/incremental_sort.out

Lines changed: 98 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1469,3 +1469,101 @@ explain (costs off) select * from t union select * from t order by 1,3;
14691469
(13 rows)
14701470

14711471
drop table t;
1472+
-- Sort pushdown can't go below where expressions are part of the rel target.
1473+
-- In particular this is interesting for volatile expressions which have to
1474+
-- go above joins since otherwise we'll incorrectly use expression evaluations
1475+
-- across multiple rows.
1476+
set enable_hashagg=off;
1477+
set enable_seqscan=off;
1478+
set enable_incremental_sort = off;
1479+
set parallel_tuple_cost=0;
1480+
set parallel_setup_cost=0;
1481+
set min_parallel_table_scan_size = 0;
1482+
set min_parallel_index_scan_size = 0;
1483+
-- Parallel sort below join.
1484+
explain (costs off) select distinct sub.unique1, stringu1
1485+
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
1486+
QUERY PLAN
1487+
--------------------------------------------------------------------------
1488+
Unique
1489+
-> Nested Loop
1490+
-> Gather Merge
1491+
Workers Planned: 2
1492+
-> Sort
1493+
Sort Key: tenk1.unique1, tenk1.stringu1
1494+
-> Parallel Index Scan using tenk1_unique1 on tenk1
1495+
-> Function Scan on generate_series
1496+
(8 rows)
1497+
1498+
explain (costs off) select sub.unique1, stringu1
1499+
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
1500+
order by 1, 2;
1501+
QUERY PLAN
1502+
--------------------------------------------------------------------
1503+
Nested Loop
1504+
-> Gather Merge
1505+
Workers Planned: 2
1506+
-> Sort
1507+
Sort Key: tenk1.unique1, tenk1.stringu1
1508+
-> Parallel Index Scan using tenk1_unique1 on tenk1
1509+
-> Function Scan on generate_series
1510+
(7 rows)
1511+
1512+
-- Parallel sort but with expression that can be safely generated at the base rel.
1513+
explain (costs off) select distinct sub.unique1, md5(stringu1)
1514+
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
1515+
QUERY PLAN
1516+
----------------------------------------------------------------------------------------
1517+
Unique
1518+
-> Nested Loop
1519+
-> Gather Merge
1520+
Workers Planned: 2
1521+
-> Sort
1522+
Sort Key: tenk1.unique1, (md5((tenk1.stringu1)::text)) COLLATE "C"
1523+
-> Parallel Index Scan using tenk1_unique1 on tenk1
1524+
-> Function Scan on generate_series
1525+
(8 rows)
1526+
1527+
explain (costs off) select sub.unique1, md5(stringu1)
1528+
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
1529+
order by 1, 2;
1530+
QUERY PLAN
1531+
----------------------------------------------------------------------------------
1532+
Nested Loop
1533+
-> Gather Merge
1534+
Workers Planned: 2
1535+
-> Sort
1536+
Sort Key: tenk1.unique1, (md5((tenk1.stringu1)::text)) COLLATE "C"
1537+
-> Parallel Index Scan using tenk1_unique1 on tenk1
1538+
-> Function Scan on generate_series
1539+
(7 rows)
1540+
1541+
-- Parallel sort but with expression not available until the upper rel.
1542+
explain (costs off) select distinct sub.unique1, stringu1 || random()::text
1543+
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
1544+
QUERY PLAN
1545+
---------------------------------------------------------------------------------------------
1546+
Unique
1547+
-> Sort
1548+
Sort Key: tenk1.unique1, (((tenk1.stringu1)::text || (random())::text)) COLLATE "C"
1549+
-> Gather
1550+
Workers Planned: 2
1551+
-> Nested Loop
1552+
-> Parallel Index Scan using tenk1_unique1 on tenk1
1553+
-> Function Scan on generate_series
1554+
(8 rows)
1555+
1556+
explain (costs off) select sub.unique1, stringu1 || random()::text
1557+
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
1558+
order by 1, 2;
1559+
QUERY PLAN
1560+
---------------------------------------------------------------------------------------
1561+
Sort
1562+
Sort Key: tenk1.unique1, (((tenk1.stringu1)::text || (random())::text)) COLLATE "C"
1563+
-> Gather
1564+
Workers Planned: 2
1565+
-> Nested Loop
1566+
-> Parallel Index Scan using tenk1_unique1 on tenk1
1567+
-> Function Scan on generate_series
1568+
(7 rows)
1569+

‎src/test/regress/sql/incremental_sort.sql

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -221,3 +221,34 @@ set enable_hashagg to off;
221221
explain (costs off)select*from tunionselect*from torder by1,3;
222222

223223
droptable t;
224+
225+
-- Sort pushdown can't go below where expressions are part of the rel target.
226+
-- In particular this is interesting for volatile expressions which have to
227+
-- go above joins since otherwise we'll incorrectly use expression evaluations
228+
-- across multiple rows.
229+
set enable_hashagg=off;
230+
set enable_seqscan=off;
231+
set enable_incremental_sort= off;
232+
set parallel_tuple_cost=0;
233+
set parallel_setup_cost=0;
234+
set min_parallel_table_scan_size=0;
235+
set min_parallel_index_scan_size=0;
236+
237+
-- Parallel sort below join.
238+
explain (costs off)select distinctsub.unique1, stringu1
239+
from tenk1, lateral (selecttenk1.unique1from generate_series(1,1000))as sub;
240+
explain (costs off)selectsub.unique1, stringu1
241+
from tenk1, lateral (selecttenk1.unique1from generate_series(1,1000))as sub
242+
order by1,2;
243+
-- Parallel sort but with expression that can be safely generated at the base rel.
244+
explain (costs off)select distinctsub.unique1, md5(stringu1)
245+
from tenk1, lateral (selecttenk1.unique1from generate_series(1,1000))as sub;
246+
explain (costs off)selectsub.unique1, md5(stringu1)
247+
from tenk1, lateral (selecttenk1.unique1from generate_series(1,1000))as sub
248+
order by1,2;
249+
-- Parallel sort but with expression not available until the upper rel.
250+
explain (costs off)select distinctsub.unique1, stringu1|| random()::text
251+
from tenk1, lateral (selecttenk1.unique1from generate_series(1,1000))as sub;
252+
explain (costs off)selectsub.unique1, stringu1|| random()::text
253+
from tenk1, lateral (selecttenk1.unique1from generate_series(1,1000))as sub
254+
order by1,2;

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp