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

Commit987f05e

Browse files
committed
Make contain_volatile_functions/contain_mutable_functions look into SubLinks.
This change prevents us from doing inappropriate subquery flattening incases such as dangerous functions hidden inside a sub-SELECT in thetargetlist of another sub-SELECT. That could result in unexpected behaviordue to multiple evaluations of a volatile function, as in a recentcomplaint from Etienne Dube. It's been questionable from the verybeginning whether these functions should look into subqueries (as noted intheir comments), and this case seems to provide proof that they should.Because the new code only descends into SubLinks, not SubPlans orInitPlans, the change only affects the planner's behavior duringprepjointree processing and not later on --- for example, you can still getit to use a volatile function in an indexqual if you wrap the function in(SELECT ...). That's a historical behavior, for sure, but it's reasonablegiven that the executor's evaluation rules for subplans don't depend onwhether there are volatile functions inside them. In any case, we need toconstrain the behavioral change as narrowly as we can to make thisreasonable to back-patch.
1 parent8103f49 commit987f05e

File tree

3 files changed

+107
-6
lines changed

3 files changed

+107
-6
lines changed

‎src/backend/optimizer/util/clauses.c

Lines changed: 27 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -786,8 +786,8 @@ contain_subplans_walker(Node *node, void *context)
786786
* mistakenly think that something like "WHERE random() < 0.5" can be treated
787787
* as a constant qualification.
788788
*
789-
*XXX we do not examine sub-selects to see if they contain uses of
790-
*mutable functions. It'snotreal clear if that is correct or not...
789+
*We will recursively look into Query nodes (i.e., SubLink sub-selects)
790+
*butnotinto SubPlans. See comments for contain_volatile_functions().
791791
*/
792792
bool
793793
contain_mutable_functions(Node*clause)
@@ -884,6 +884,13 @@ contain_mutable_functions_walker(Node *node, void *context)
884884
}
885885
/* else fall through to check args */
886886
}
887+
elseif (IsA(node,Query))
888+
{
889+
/* Recurse into subselects */
890+
returnquery_tree_walker((Query*)node,
891+
contain_mutable_functions_walker,
892+
context,0);
893+
}
887894
returnexpression_tree_walker(node,contain_mutable_functions_walker,
888895
context);
889896
}
@@ -898,11 +905,18 @@ contain_mutable_functions_walker(Node *node, void *context)
898905
* Recursively search for volatile functions within a clause.
899906
*
900907
* Returns true if any volatile function (or operator implemented by a
901-
* volatile function) is found. This test prevents invalid conversions
902-
* of volatile expressions into indexscan quals.
908+
* volatile function) is found. This test prevents, for example,
909+
*invalid conversionsof volatile expressions into indexscan quals.
903910
*
904-
* XXX we do not examine sub-selects to see if they contain uses of
905-
* volatile functions.It's not real clear if that is correct or not...
911+
* We will recursively look into Query nodes (i.e., SubLink sub-selects)
912+
* but not into SubPlans. This is a bit odd, but intentional.If we are
913+
* looking at a SubLink, we are probably deciding whether a query tree
914+
* transformation is safe, and a contained sub-select should affect that;
915+
* for example, duplicating a sub-select containing a volatile function
916+
* would be bad. However, once we've got to the stage of having SubPlans,
917+
* subsequent planning need not consider volatility within those, since
918+
* the executor won't change its evaluation rules for a SubPlan based on
919+
* volatility.
906920
*/
907921
bool
908922
contain_volatile_functions(Node*clause)
@@ -1000,6 +1014,13 @@ contain_volatile_functions_walker(Node *node, void *context)
10001014
}
10011015
/* else fall through to check args */
10021016
}
1017+
elseif (IsA(node,Query))
1018+
{
1019+
/* Recurse into subselects */
1020+
returnquery_tree_walker((Query*)node,
1021+
contain_volatile_functions_walker,
1022+
context,0);
1023+
}
10031024
returnexpression_tree_walker(node,contain_volatile_functions_walker,
10041025
context);
10051026
}

‎src/test/regress/expected/subselect.out

Lines changed: 64 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -639,3 +639,67 @@ where a.thousand = b.thousand
639639
----------
640640
(0 rows)
641641

642+
--
643+
-- Check that nested sub-selects are not pulled up if they contain volatiles
644+
--
645+
explain (verbose, costs off)
646+
select x, x from
647+
(select (select now()) as x from (values(1),(2)) v(y)) ss;
648+
QUERY PLAN
649+
---------------------------
650+
Values Scan on "*VALUES*"
651+
Output: $0, $1
652+
InitPlan 1 (returns $0)
653+
-> Result
654+
Output: now()
655+
InitPlan 2 (returns $1)
656+
-> Result
657+
Output: now()
658+
(8 rows)
659+
660+
explain (verbose, costs off)
661+
select x, x from
662+
(select (select random()) as x from (values(1),(2)) v(y)) ss;
663+
QUERY PLAN
664+
----------------------------------
665+
Subquery Scan on ss
666+
Output: ss.x, ss.x
667+
-> Values Scan on "*VALUES*"
668+
Output: $0
669+
InitPlan 1 (returns $0)
670+
-> Result
671+
Output: random()
672+
(7 rows)
673+
674+
explain (verbose, costs off)
675+
select x, x from
676+
(select (select now() where y=y) as x from (values(1),(2)) v(y)) ss;
677+
QUERY PLAN
678+
--------------------------------------
679+
Values Scan on "*VALUES*"
680+
Output: (SubPlan 1), (SubPlan 2)
681+
SubPlan 1
682+
-> Result
683+
Output: now()
684+
One-Time Filter: ($0 = $0)
685+
SubPlan 2
686+
-> Result
687+
Output: now()
688+
One-Time Filter: ($1 = $1)
689+
(10 rows)
690+
691+
explain (verbose, costs off)
692+
select x, x from
693+
(select (select random() where y=y) as x from (values(1),(2)) v(y)) ss;
694+
QUERY PLAN
695+
--------------------------------------------
696+
Subquery Scan on ss
697+
Output: ss.x, ss.x
698+
-> Values Scan on "*VALUES*"
699+
Output: (SubPlan 1)
700+
SubPlan 1
701+
-> Result
702+
Output: random()
703+
One-Time Filter: ($0 = $0)
704+
(8 rows)
705+

‎src/test/regress/sql/subselect.sql

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -389,3 +389,19 @@ where a.thousand = b.thousand
389389
and exists (select1from tenk1 cwhereb.hundred=c.hundred
390390
and not exists (select1from tenk1 d
391391
wherea.thousand=d.thousand ) );
392+
393+
--
394+
-- Check that nested sub-selects are not pulled up if they contain volatiles
395+
--
396+
explain (verbose, costs off)
397+
select x, xfrom
398+
(select (select now())as xfrom (values(1),(2)) v(y)) ss;
399+
explain (verbose, costs off)
400+
select x, xfrom
401+
(select (select random())as xfrom (values(1),(2)) v(y)) ss;
402+
explain (verbose, costs off)
403+
select x, xfrom
404+
(select (select now()where y=y)as xfrom (values(1),(2)) v(y)) ss;
405+
explain (verbose, costs off)
406+
select x, xfrom
407+
(select (select random()where y=y)as xfrom (values(1),(2)) v(y)) ss;

0 commit comments

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