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