protected function _checkRequiredOptions(array $config)
    {
        parent::_checkRequiredOptions($config);

        if (array_key_exists('host', $this->_config) &&
        !array_key_exists('port', $config)) {
            /** @see Zend_Db_Adapter_Exception */
            // require_once 'Zend/Db/Adapter/Exception.php';
            throw new Zend_Db_Adapter_Exception("Configuration must have a key for 'port' when 'host' is specified");
        }
    }