protected static function _createCacheKey($query, $parameters, $table_name = null, $connection_name = self::DEFAULT_CONNECTION)
        {
            if(isset(self::$_config[$connection_name]['create_cache_key']) && is_callable(self::$_config[$connection_name]['create_cache_key'])) {
                return call_user_func_array(self::$_config[$connection_name]['create_cache_key'], array($query, $parameters, $table_name, $connection_name));
            }

            $parameter_string = join(',', $parameters);
            $key = $query . ':' . $parameter_string;

            return sha1($key);
        }