minor_fix_by_kuroda.diff

diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index b0233786d4..77ae17073a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -1152,13 +1152,13 @@ drop_failover_replication_slots(struct LogicalRepInfo *dbinfo)
 	conn = connect_database(dbinfo[0].subconninfo, false);
 	if (conn != NULL)
 	{
-		/* Get failover replication slot names. */
+		/* Get failover replication slot names */
 		res = PQexec(conn,
 					 "SELECT slot_name FROM pg_catalog.pg_replication_slots WHERE failover");
 
 		if (PQresultStatus(res) == PGRES_TUPLES_OK)
 		{
-			/* Remove failover replication slots from subscriber. */
+			/* Remove failover replication slots from subscriber */
 			for (int i = 0; i < PQntuples(res); i++)
 				drop_replication_slot(conn, &dbinfo[0], PQgetvalue(res, i, 0));
 		}
@@ -1310,7 +1310,11 @@ start_standby_server(const struct CreateSubscriberOptions *opt, bool restricted_
 	PQExpBuffer pg_ctl_cmd = createPQExpBuffer();
 	int			rc;
 
-	appendPQExpBuffer(pg_ctl_cmd, "\"%s\" start -D \"%s\" -s -o \"-c sync_replication_slots=off\"",
+	/*
+	 * FIXME: appending "sync_replication_slots=off" is not trivial for reader.
+	 * Please separate it into the later part with comments.
+	 */
+	appendPQExpBuffer(pg_ctl_cmd, "\"%s\" start -D \"%s\" -s",
 					  pg_ctl_path, subscriber_dir);
 	if (restricted_access)
 	{
@@ -1333,6 +1337,24 @@ start_standby_server(const struct CreateSubscriberOptions *opt, bool restricted_
 	if (opt->config_file != NULL)
 		appendPQExpBuffer(pg_ctl_cmd, " -o \"-c config_file=%s\"",
 						  opt->config_file);
+
+	/*
+	 * FIXME: please describe why the sync_replication_slots is set to false.
+	 * I.e.,
+	 */
+
+	/*
+	 * We set up some recovery parameters in the middle part of the
+	 * pg_createsubscriber to ensure all changes are caught up. At that time,
+	 * primary_conninfo will be set without the dbname attribute. Basically, it
+	 * works well, but if the slot sync is enabled, the slot sync worker will
+	 * exit with ERROR because the process requires dbname within
+	 * primary_conninfo. To avoid the error, we override sync_replication_slots
+	 * to off. The synchronization won't happen after the conversion, so it is
+	 * acceptable to stop here as well.
+	 */
+	appendPQExpBuffer(pg_ctl_cmd, " -o \"-c sync_replication_slots=off\"");
+
 	pg_log_debug("pg_ctl command is: %s", pg_ctl_cmd->data);
 	rc = system(pg_ctl_cmd->data);
 	pg_ctl_status(pg_ctl_cmd->data, rc);
@@ -2068,6 +2090,7 @@ main(int argc, char **argv)
 	/* Check if the primary server is ready for logical replication */
 	pub_failed = check_publisher(dbinfo);
 
+	/* Exit if either of them is not ready */
 	if (pub_failed || sub_failed)
 		exit(1);
 
@@ -2111,8 +2134,8 @@ main(int argc, char **argv)
 	setup_subscriber(dbinfo, consistent_lsn);
 
 	/*
-	 * Remove primary_slot_name if it exists on primary.  This replication slot
-	 * has no use after the transformation.
+	 * Remove primary_slot_name if it exists on primary.  This replication
+	 * slot has no use after the transformation.
 	 */
 	drop_primary_replication_slot(dbinfo, primary_slot_name);
 
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 0516d4e17e..cc65942dc4 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -266,28 +266,43 @@ $node_p->restart;
 # Create failover slot to test its removal
 my $fslotname = 'failover_slot';
 $node_p->safe_psql('pg1',
-	"SELECT pg_create_logical_replication_slot('$fslotname', 'pgoutput', false, false, true)");
+	"SELECT pg_create_logical_replication_slot('$fslotname', 'pgoutput', false, false, true)"
+);
 $node_s->start;
 $node_s->safe_psql('postgres', "SELECT pg_sync_replication_slots()");
-my $result = $node_s->safe_psql('postgres', "SELECT slot_name FROM pg_replication_slots WHERE slot_name = '$fslotname' AND synced AND NOT temporary");
+my $result = $node_s->safe_psql('postgres',
+	"SELECT slot_name FROM pg_replication_slots WHERE slot_name = '$fslotname' AND synced AND NOT temporary"
+);
 is($result, 'failover_slot', 'failover slot is synced');
 $node_s->stop;
 
 # dry run mode on node S
 command_ok(
 	[
-		'pg_createsubscriber', '--verbose',
-		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
-		'--dry-run', '--pgdata',
-		$node_s->data_dir, '--publisher-server',
-		$node_p->connstr('pg1'), '--socket-directory',
-		$node_s->host, '--subscriber-port',
-		$node_s->port, '--publication',
-		'pub1', '--publication',
-		'pub2', '--subscription',
-		'sub1', '--subscription',
-		'sub2', '--database',
-		'pg1', '--database',
+		'pg_createsubscriber',
+		'--verbose',
+		'--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default",
+		'--dry-run',
+		'--pgdata',
+		$node_s->data_dir,
+		'--publisher-server',
+		$node_p->connstr('pg1'),
+		'--socket-directory',
+		$node_s->host,
+		'--subscriber-port',
+		$node_s->port,
+		'--publication',
+		'pub1',
+		'--publication',
+		'pub2',
+		'--subscription',
+		'sub1',
+		'--subscription',
+		'sub2',
+		'--database',
+		'pg1',
+		'--database',
 		'pg2'
 	],
 	'run pg_createsubscriber --dry-run on node S');
@@ -314,18 +329,30 @@ command_ok(
 # Run pg_createsubscriber on node S
 command_ok(
 	[
-		'pg_createsubscriber', '--verbose',
-		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
-		'--verbose', '--pgdata',
-		$node_s->data_dir, '--publisher-server',
-		$node_p->connstr('pg1'), '--socket-directory',
-		$node_s->host, '--subscriber-port',
-		$node_s->port, '--publication',
-		'pub1', '--publication',
-		'Pub2', '--replication-slot',
-		'replslot1', '--replication-slot',
-		'replslot2', '--database',
-		'pg1', '--database',
+		'pg_createsubscriber',
+		'--verbose',
+		'--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default",
+		'--verbose',
+		'--pgdata',
+		$node_s->data_dir,
+		'--publisher-server',
+		$node_p->connstr('pg1'),
+		'--socket-directory',
+		$node_s->host,
+		'--subscriber-port',
+		$node_s->port,
+		'--publication',
+		'pub1',
+		'--publication',
+		'Pub2',
+		'--replication-slot',
+		'replslot1',
+		'--replication-slot',
+		'replslot2',
+		'--database',
+		'pg1',
+		'--database',
 		'pg2'
 	],
 	'run pg_createsubscriber on node S');
@@ -358,7 +385,8 @@ $node_s->wait_for_subscription_sync($node_p, $subnames[1]);
 
 # Confirm the failover slot has been removed
 $result = $node_s->safe_psql('pg1',
-	"SELECT count(*) FROM pg_replication_slots WHERE slot_name = '$fslotname'");
+	"SELECT count(*) FROM pg_replication_slots WHERE slot_name = '$fslotname'"
+);
 is($result, qq(0), 'failover slot was removed');
 
 # Check result on database pg1