Allow altering of two_phase option of a SUBSCRIPTION.

The two_phase option is controlled by both the publisher (as a slot
option) and the subscriber (as a subscription option), so the slot option
must also be modified.

Changing the 'two_phase' option for a subscription from 'true' to 'false'
is permitted only when there are no pending prepared transactions
corresponding to that subscription. Otherwise, the changes of already
prepared transactions can be replicated again along with their corresponding
commit leading to duplicate data or errors.

To avoid data loss, the 'two_phase' option for a subscription can only be
changed from 'false' to 'true' once the initial data synchronization is
completed. Therefore this is performed later by the logical replication worker.

Author: Hayato Kuroda, Ajin Cherian, Amit Kapila
Reviewed-by: Peter Smith, Hou Zhijie, Amit Kapila, Vitaly Davydov, Vignesh C
Discussion: https://postgr.es/m/8fab8-65d74c80-1-2f28e880@39088166

1 files changed, 93 insertions, 2 deletions

diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b7..a47d3b7dd6e 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,99 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Alter the subscription to set two_phase to false.
+# Verify that the altered subscription reflects the new two_phase option.
+###############################
+
+# Confirm that the two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
+
+###############################
+# Now do a prepare on the publisher and verify that it is not replicated.
+###############################
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+###############################
+# Set two_phase to "true" and failover to "true" before the COMMIT PREPARED.
+#
+# This tests the scenario where both two_phase and failover are altered
+# simultaneously.
+###############################
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+###############################
+# Now commit the insert and verify that it is replicated.
+###############################
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +467,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');