From 2db576ba8c449fcaf61ae7aa14ed62e63ebf5924 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 11 Dec 2014 19:37:00 -0500
Subject: [PATCH] Fix corner case where SELECT FOR UPDATE could return a row
twice.
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.
---
src/backend/executor/nodeLockRows.c | 22 ++++++++++++++++++
.../isolation/expected/eval-plan-qual.out | 23 +++++++++++++++++++
src/test/isolation/specs/eval-plan-qual.spec | 16 +++++++++++++
3 files changed, 61 insertions(+)
diff --git a/src/backend/executor/nodeLockRows.c b/src/backend/executor/nodeLockRows.c
index 990240bf0a8..5dcb9b042ac 100644
--- a/src/backend/executor/nodeLockRows.c
+++ b/src/backend/executor/nodeLockRows.c
@@ -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;
}
diff --git a/src/test/isolation/expected/eval-plan-qual.out b/src/test/isolation/expected/eval-plan-qual.out
index ab778cbd7aa..0f6595fcb1b 100644
--- a/src/test/isolation/expected/eval-plan-qual.out
+++ b/src/test/isolation/expected/eval-plan-qual.out
@@ -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;
diff --git a/src/test/isolation/specs/eval-plan-qual.spec b/src/test/isolation/specs/eval-plan-qual.spec
index 786b7913652..876e5470dba 100644
--- a/src/test/isolation/specs/eval-plan-qual.spec
+++ b/src/test/isolation/specs/eval-plan-qual.spec
@@ -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"
--
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