public static function instance($name = 'default')
	{
		if (\array_key_exists($name, static::$instances))
		{
			return static::$instances[$name];
		}

		if (empty(static::$instances))
		{
			\Config::load('db', true);
		}

		if ( ! ($config = \Config::get('db.mongo.'.$name)))
		{
			throw new \Mongo_DbException('Invalid instance name given.');
		}

		static::$instances[$name] = new static($config);

		return static::$instances[$name];
	}