前言
这里说的是mysql配置，首先排除网络问题，在网络通信良好的情况下，我们来探究mysql问题。
现象
在内网远程访问mysql特别慢
排查
因为刚刚解决了内网连接linux 速度特慢的问题，所以猜测mysql可能也会有DNS反向解析导致。
解决办法
可以在配置文件里面禁止MySQL进行反向DNS解析,
只需在my.cnf的[mysqld]段落中加入如下行：
[mysqld]
skip-name-resolve 然后重启mysql服务即可。
扩展阅读
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.
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If you don’t want to allow connections over TCP/IP, you can do this by starting mysqld with –skip-networking.
