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Fix corner case where SELECT FOR UPDATE could return a row twice.

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In READ COMMITTED mode, if a SELECT FOR UPDATE discovers it has to redo
WHERE-clause checking on rows that have been updated since the SELECT's
snapshot, it invokes EvalPlanQual processing to do that.  If this first
occurs within a non-first child table of an inheritance tree, the previous
coding could accidentally re-return a matching row from an earlier,
already-scanned child table.  (And, to add insult to injury, I think this
could make it miss returning a row that should have been returned, if the
updated row that this happens on should still have passed the WHERE qual.)
Per report from Kyotaro Horiguchi; the added isolation test is based on his
test case.

This has been broken for quite awhile, so back-patch to all supported
branches.
This commit is contained in:
Tom Lane 2014-12-11 19:37:00 -05:00
parent 2646d2d4a9
commit 2db576ba8c
3 changed files with 61 additions and 0 deletions
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22
src/backend/executor/nodeLockRows.c
View File

@ -194,7 +194,29 @@ lnext:
*/
if (!epq_started)
{
ListCell *lc2;
EvalPlanQualBegin(&node->lr_epqstate, estate);
/*
* Ensure that rels with already-visited rowmarks are told
* not to return tuples during the first EPQ test. We can
* exit this loop once it reaches the current rowmark;
* rels appearing later in the list will be set up
* correctly by the EvalPlanQualSetTuple call at the top
* of the loop.
*/
foreach(lc2, node->lr_arowMarks)
{
ExecAuxRowMark *aerm2 = (ExecAuxRowMark *) lfirst(lc2);
if (lc2 == lc)
break;
EvalPlanQualSetTuple(&node->lr_epqstate,
aerm2->rowmark->rti,
NULL);
}
epq_started = true;
}

23
src/test/isolation/expected/eval-plan-qual.out
View File

@ -49,3 +49,26 @@ accountid balance
checking 600
savings 2334
starting permutation: readp1 writep1 readp2 c1 c2
step readp1: SELECT tableoid::regclass, ctid, * FROM p WHERE b IN (0, 1) AND c = 0 FOR UPDATE;
tableoid ctid a b c
c1 (0,1) 0 0 0
c1 (0,4) 0 1 0
c2 (0,1) 1 0 0
c2 (0,4) 1 1 0
c3 (0,1) 2 0 0
c3 (0,4) 2 1 0
step writep1: UPDATE p SET b = -1 WHERE a = 1 AND b = 1 AND c = 0;
step readp2: SELECT tableoid::regclass, ctid, * FROM p WHERE b IN (0, 1) AND c = 0 FOR UPDATE; <waiting ...>
step c1: COMMIT;
step readp2: <... completed>
tableoid ctid a b c
c1 (0,1) 0 0 0
c1 (0,4) 0 1 0
c2 (0,1) 1 0 0
c3 (0,1) 2 0 0
c3 (0,4) 2 1 0
step c2: COMMIT;

16
src/test/isolation/specs/eval-plan-qual.spec
View File

@ -8,11 +8,20 @@ setup
{
CREATE TABLE accounts (accountid text PRIMARY KEY, balance numeric not null);
INSERT INTO accounts VALUES ('checking', 600), ('savings', 600);
CREATE TABLE p (a int, b int, c int);
CREATE TABLE c1 () INHERITS (p);
CREATE TABLE c2 () INHERITS (p);
CREATE TABLE c3 () INHERITS (p);
INSERT INTO c1 SELECT 0, a / 3, a % 3 FROM generate_series(0, 9) a;
INSERT INTO c2 SELECT 1, a / 3, a % 3 FROM generate_series(0, 9) a;
INSERT INTO c3 SELECT 2, a / 3, a % 3 FROM generate_series(0, 9) a;
}
teardown
{
DROP TABLE accounts;
DROP TABLE p CASCADE;
}
session "s1"
@ -30,6 +39,11 @@ step "upsert1" {
INSERT INTO accounts SELECT 'savings', 500
WHERE NOT EXISTS (SELECT 1 FROM upsert);
}
# tests with table p check inheritance cases, specifically a bug where
# nodeLockRows did the wrong thing when the first updated tuple was in
# a non-first child table
step "readp1" { SELECT tableoid::regclass, ctid, * FROM p WHERE b IN (0, 1) AND c = 0 FOR UPDATE; }
step "writep1" { UPDATE p SET b = -1 WHERE a = 1 AND b = 1 AND c = 0; }
step "c1" { COMMIT; }
session "s2"
@ -44,6 +58,7 @@ step "upsert2" {
INSERT INTO accounts SELECT 'savings', 1234
WHERE NOT EXISTS (SELECT 1 FROM upsert);
}
step "readp2" { SELECT tableoid::regclass, ctid, * FROM p WHERE b IN (0, 1) AND c = 0 FOR UPDATE; }
step "c2" { COMMIT; }
session "s3"
@ -54,3 +69,4 @@ teardown { COMMIT; }
permutation "wx1" "wx2" "c1" "c2" "read"
permutation "wy1" "wy2" "c1" "c2" "read"
permutation "upsert1" "upsert2" "c1" "c2" "read"
permutation "readp1" "writep1" "readp2" "c1" "c2"