static function getDatabase($id = 'proxy')
    {
        if ($id == 'proxy')
        {
            if (!self::$proxy)
            {
                self::$proxy = new \IMooc\Database\Proxy;
            }
            return self::$proxy;
        }
 
        $key = 'database_'.$id;
        if ($id == 'slave')
        {
            $slaves = Application::getInstance()->config['database']['slave'];
            $db_conf = $slaves[array_rand($slaves)];
        }
        else
        {//这里单例出来的只是配置信息
            $db_conf = Application::getInstance()->config['database'][$id];
        }
        $db = Register::get($key);
        if (!$db) {
            $db = new Database\MySQLi();
           //根据配置信息实例$db,并储存到注册器数组中
            $db->connect($db_conf['host'], $db_conf['user'], $db_conf['password'], $db_conf['dbname']);
            Register::set($key, $db);
        }
        return $db;
    }

第二个问题问什么？