mysql 5.5以上脚本连接数据库很慢

2014-10-10 4,483 0 技术 大超超。

解决方法:在mysql配置文件里添加一项配置。

[mysqld]

skip-name-resolve

但是在实际操作中,添加这行之后,数据库连接不上了。

另外有多个网站需要更改这样的配置,导致成本高。

mysql连接的时候不是要域名解析嘛,那就hosts文件试试,加上一行:

127.0.0.1 localhost

测试时速度很快,这样mysql连接速度慢的问题就解决了。


141010-mysql.png

附官方解释:

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.


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