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Commitbcbecbc

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Don't propagate a null subtransaction snapshot up to parent transaction.
This oversight could cause logical decoding to fail to decode an outertransaction containing changes, if a subtransaction had an XID but noactual changes. Per bug #14279 from Marko Tiikkaja. Patch by Markobased on analysis by Andrew Gierth.Discussion: <20160804191757.1430.39011@wrigleys.postgresql.org>
1 parent3676631 commitbcbecbc

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3 files changed

+40
-6
lines changed

3 files changed

+40
-6
lines changed

‎contrib/test_decoding/expected/xact.out

Lines changed: 23 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -6,9 +6,9 @@ SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_d
66
init
77
(1 row)
88

9-
-- bug #13844, xids in non-decoded records need to be inspected
109
CREATE TABLE xact_test(data text);
1110
INSERT INTO xact_test VALUES ('before-test');
11+
-- bug #13844, xids in non-decoded records need to be inspected
1212
BEGIN;
1313
-- perform operation in xact that creates and logs xid, but isn't decoded
1414
SELECT * FROM xact_test FOR UPDATE;
@@ -33,6 +33,28 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
3333
COMMIT
3434
(6 rows)
3535

36+
-- bug #14279, do not propagate null snapshot from subtransaction
37+
BEGIN;
38+
-- first insert
39+
INSERT INTO xact_test VALUES ('main-txn');
40+
SAVEPOINT foo;
41+
-- now perform operation in subxact that creates and logs xid, but isn't decoded
42+
SELECT 1 FROM xact_test FOR UPDATE LIMIT 1;
43+
?column?
44+
----------
45+
1
46+
(1 row)
47+
48+
COMMIT;
49+
-- and now show those changes
50+
SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
51+
data
52+
-------------------------------------------------------
53+
BEGIN
54+
table public.xact_test: INSERT: data[text]:'main-txn'
55+
COMMIT
56+
(3 rows)
57+
3658
DROP TABLE xact_test;
3759
SELECT pg_drop_replication_slot('regression_slot');
3860
pg_drop_replication_slot

‎contrib/test_decoding/sql/xact.sql

Lines changed: 12 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3,10 +3,10 @@ SET synchronous_commit = on;
33

44
SELECT'init'FROM pg_create_logical_replication_slot('regression_slot','test_decoding');
55

6-
-- bug #13844, xids in non-decoded records need to be inspected
76
CREATETABLExact_test(datatext);
87
INSERT INTO xact_testVALUES ('before-test');
98

9+
-- bug #13844, xids in non-decoded records need to be inspected
1010
BEGIN;
1111
-- perform operation in xact that creates and logs xid, but isn't decoded
1212
SELECT*FROM xact_test FORUPDATE;
@@ -17,6 +17,17 @@ COMMIT;
1717
-- and now show those changes
1818
SELECT dataFROM pg_logical_slot_get_changes('regression_slot',NULL,NULL,'include-xids','0','skip-empty-xacts','1');
1919

20+
-- bug #14279, do not propagate null snapshot from subtransaction
21+
BEGIN;
22+
-- first insert
23+
INSERT INTO xact_testVALUES ('main-txn');
24+
SAVEPOINT foo;
25+
-- now perform operation in subxact that creates and logs xid, but isn't decoded
26+
SELECT1FROM xact_test FORUPDATELIMIT1;
27+
COMMIT;
28+
-- and now show those changes
29+
SELECT dataFROM pg_logical_slot_get_changes('regression_slot',NULL,NULL,'include-xids','0','skip-empty-xacts','1');
30+
2031
DROPTABLE xact_test;
2132

2233
SELECT pg_drop_replication_slot('regression_slot');

‎src/backend/replication/logical/reorderbuffer.c

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -807,13 +807,14 @@ ReorderBufferCommitChild(ReorderBuffer *rb, TransactionId xid,
807807
elog(ERROR,"subxact logged without previous toplevel record");
808808

809809
/*
810-
* Passtheour base snapshot to the parent transaction if it doesn't have
810+
* Pass our base snapshot to the parent transaction if it doesn't have
811811
* one, or ours is older. That can happen if there are no changes in the
812812
* toplevel transaction but in one of the child transactions. This allows
813-
* the parent to simply useit's base snapshot initially.
813+
* the parent to simply useits base snapshot initially.
814814
*/
815-
if (txn->base_snapshot==NULL||
816-
txn->base_snapshot_lsn>subtxn->base_snapshot_lsn)
815+
if (subtxn->base_snapshot!=NULL&&
816+
(txn->base_snapshot==NULL||
817+
txn->base_snapshot_lsn>subtxn->base_snapshot_lsn))
817818
{
818819
txn->base_snapshot=subtxn->base_snapshot;
819820
txn->base_snapshot_lsn=subtxn->base_snapshot_lsn;

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