Don't propagate a null subtransaction snapshot up to parent transaction.

This oversight could cause logical decoding to fail to decode an outer
transaction containing changes, if a subtransaction had an XID but no
actual changes.  Per bug #14279 from Marko Tiikkaja.  Patch by Marko
based on analysis by Andrew Gierth.

Discussion: <20160804191757.1430.39011@wrigleys.postgresql.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/contrib/test_decoding/sql/xact.sql b/contrib/test_decoding/sql/xact.sql
index 9ce238f62df..aa555911e86 100644
--- a/contrib/test_decoding/sql/xact.sql
+++ b/contrib/test_decoding/sql/xact.sql
@@ -3,10 +3,10 @@ SET synchronous_commit = on;
 
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
 
--- bug #13844, xids in non-decoded records need to be inspected
 CREATE TABLE xact_test(data text);
 INSERT INTO xact_test VALUES ('before-test');
 
+-- bug #13844, xids in non-decoded records need to be inspected
 BEGIN;
 -- perform operation in xact that creates and logs xid, but isn't decoded
 SELECT * FROM xact_test FOR UPDATE;
@@ -17,6 +17,17 @@ COMMIT;
 -- and now show those changes
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
+-- bug #14279, do not propagate null snapshot from subtransaction
+BEGIN;
+-- first insert
+INSERT INTO xact_test VALUES ('main-txn');
+SAVEPOINT foo;
+-- now perform operation in subxact that creates and logs xid, but isn't decoded
+SELECT 1 FROM xact_test FOR UPDATE LIMIT 1;
+COMMIT;
+-- and now show those changes
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+
 DROP TABLE xact_test;
 
 SELECT pg_drop_replication_slot('regression_slot');