Set synchronous_commit to off for current session

Forward-ported from 2.x; need to verify it makes sense.

dbutils.c

@@ -804,3 +804,29 @@ stop_backup(PGconn *conn, char *last_wal_segment)
 
 	return true;
 }
+
+
+bool
+set_config_bool(PGconn *conn, const char *config_param, bool state)
+{
+	char		sqlquery[QUERY_STR_LEN];
+	PGresult   *res;
+
+	sqlquery_snprintf(sqlquery,
+					  "SET %s TO %s",
+					  config_param,
+					  state ? "TRUE" : "FALSE");
+
+	res = PQexec(conn, sqlquery);
+
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		log_err("Unable to set '%s': %s\n", config_param, PQerrorMessage(conn));
+		PQclear(res);
+		return false;
+	}
+
+	PQclear(res);
+
+	return true;
+}

dbutils.h

@@ -57,5 +57,6 @@ bool		create_replication_slot(PGconn *conn, char *slot_name);
 
 bool		start_backup(PGconn *conn, char *first_wal_segment);
 bool		stop_backup(PGconn *conn, char *last_wal_segment);
+bool		set_config_bool(PGconn *conn, const char *config_param, bool state);
 
 #endif

repmgr.c

@@ -1114,6 +1114,17 @@ do_standby_clone(void)
 
 	if(runtime_options.rsync_only)
 	{
+
+		/*
+		 * From pg 9.1 default is to wait for a sync standby to ack, avoid that by
+		 * turning off sync rep for this session
+		 */
+		if(set_config_bool(primary_conn, "synchronous_commit", false) == false)
+		{
+			PQfinish(primary_conn);
+			exit(ERR_BAD_CONFIG);
+		}
+
 		if(start_backup(primary_conn, first_wal_segment) == false)
 		{
 			r = ERR_BAD_BASEBACKUP;