Slow mysql connection _ MySQL

Slow mysql connection:
Today, it is found that website access to the database is slow. after investigation, it is very fast to query the database and it is time-consuming to connect to the database.

Solution:
In the mysql configuration file my. cnf, add this configuration under [mysqld.

Appendix: in the [mysqld] section, you must add the skip-name-resolve parameter: the host name is not resolved. The value of the Host column in the authorization table must be an IP number or localhost.

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 call, 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 have 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