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Fix misbehavior of CTE-used-in-a-subplan during EPQ rechecks.

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An updating query that reads a CTE within an InitPlan or SubPlan could get
incorrect results if it updates rows that are concurrently being modified.
This is caused by CteScanNext supposing that nothing inside its recursive
ExecProcNode call could change which read pointer is selected in the CTE's
shared tuplestore.  While that's normally true because of scoping
considerations, it can break down if an EPQ plan tree gets built during the
call, because EvalPlanQualStart builds execution trees for all subplans
whether they're going to be used during the recheck or not.  And it seems
like a pretty shaky assumption anyway, so let's just reselect our own read
pointer here.

Per bug #14870 from Andrei Gorita.  This has been broken since CTEs were
implemented, so back-patch to all supported branches.

Discussion: https://postgr.es/m/20171024155358.1471.82377@wrigleys.postgresql.org
This commit is contained in:
Tom Lane
2018-02-19 16:00:18 -05:00
parent 4108a28d3a
commit 159efe4af4
3 changed files with 37 additions and 0 deletions
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15
src/test/isolation/expected/eval-plan-qual.out
View File

@ -217,3 +217,18 @@ id data id data
9 0 9 0
10 0 10 0
step c1: COMMIT;
starting permutation: wrtwcte multireadwcte c1 c2
step wrtwcte: UPDATE table_a SET value = 'tableAValue2' WHERE id = 1;
step multireadwcte:
WITH updated AS (
UPDATE table_a SET value = 'tableAValue3' WHERE id = 1 RETURNING id
)
SELECT (SELECT id FROM updated) AS subid, * FROM updated;
<waiting ...>
step c1: COMMIT;
step c2: COMMIT;
step multireadwcte: <... completed>
subid id
1 1

9
src/test/isolation/specs/eval-plan-qual.spec
View File

@ -139,6 +139,14 @@ step "readwcte" {
SELECT * FROM cte2;
}
# this test exercises a different CTE misbehavior, cf bug #14870
step "multireadwcte" {
WITH updated AS (
UPDATE table_a SET value = 'tableAValue3' WHERE id = 1 RETURNING id
)
SELECT (SELECT id FROM updated) AS subid, * FROM updated;
}
teardown { COMMIT; }
permutation "wx1" "wx2" "c1" "c2" "read"
@ -151,3 +159,4 @@ permutation "wx2" "lockwithvalues" "c2" "c1" "read"
permutation "updateforss" "readforss" "c1" "c2"
permutation "wrtwcte" "readwcte" "c1" "c2"
permutation "wrjt" "selectjoinforupdate" "c2" "c1"
permutation "wrtwcte" "multireadwcte" "c1" "c2"