def restore_configuration_files(self):
        """ restore a previously saved postgresql.conf """
        try:
            for f in self._configuration_to_save:
                config_file = os.path.join(self._config_dir, f)
                backup_file = os.path.join(self._data_dir, f + '.backup')
                if not os.path.isfile(config_file):
                    if os.path.isfile(backup_file):
                        shutil.copy(backup_file, config_file)
                    # Previously we didn't backup pg_ident.conf, if file is missing just create empty
                    elif f == 'pg_ident.conf':
                        open(config_file, 'w').close()
        except IOError:
            logger.exception('unable to restore configuration files from backup')