def _get_relay_log(server):
    """Retrieve relay log and relay log position

    server[in]        Server instance

    Returns tuple (relay log, relay log position)
    """
    relay_log, relay_log_pos = '', ''
    res = server.exec_query("SHOW SLAVE STATUS")
    if res != [] and res is not None:
        relay_log = res[0][7]
        relay_log_pos = res[0][8]
    return relay_log, relay_log_pos