Phenomenon:
Now found that the site access to the database is slow, after checking, query the database quickly, the connection database is time-consuming.
Workaround:
In MySQL configuration file my.cnf, add this configuration under [Mysqld].
Appendix: [Mysqld] section to add a parameter skip-name-resolve: Host name is not parsed. The column value of Host in the authorization table must be an IP number or localhost after the join.
How MySQL uses DNS
When a new thread connects to Mysqld, Mysqld would spawn a new thread to handle the request. This thread would first check if the hostname is in the hostname cache. If not the thread would call Gethostbyaddr_r () and Gethostbyname_r () to resolve the hostname.
If the operating system doesn ' t support the above Thread-safe calls, the thread would lock a mutex and call gethostbyaddr () and gethostbyname () instead. Note that in this case no other thread can resolve other hostnames that's not in the hostname cache until the first Threa D 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 had a very slow DNS and many hosts, you can get to more performance by either disabling DNS Lookop with--skip-name-r Esolve 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
