现象描述：

• 本机连接mysql速度很快
• 远程连接mysql速度需要等待30秒左右
• 远程连接后访问mysql中的表正常

问题原因是由于mysql对连接的客户端进行DNS反向解析。

官方文档关于DNS的说明：

How MySQL uses DNS
When a new thread connects to mysqld, mysqld will spawn a new thread to handle the request. This thread will first check if the hostname is in the hostname cache. If not the thread will call gethostbyaddr_r() and gethostbyname_r() to resolve the hostname.
If the operating system doesn't support the above thread-safe calls, the thread will lock a mutex and call gethostbyaddr() and gethostbyname() instead. Note that in this case no other thread can resolve other hostnames that is not in the hostname cache until the first thread is ready.
You can disable DNS host lookup by starting mysqld with –skip-name-resolve. In this case you can however only use IP names in the MySQL privilege tables.
If you have a very slow DNS and many hosts, you can get more performance by either disabling DNS lookop with –skip-name-resolve or by increasing the HOST_CACHE_SIZE define (default: 128) and recompile mysqld.
You can disable the hostname cache with –skip-host-cache. You can clear the hostname cache with FLUSH HOSTS or mysqladmin flush-hosts.
If you don't want to allow connections over TCP/IP, you can do this by starting mysqld with –skip-networking.

解决方案：

可以在docker 启动命令加入：

docker run --name some-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mysql:8.0.15 --character-set-server=utf8mb4 --skip-name-resolve

或者在my.cnf中添加如下配置
[mysqld]
skip-name-resolve

重启mysql服务