Is your MySQL really slow without actually being too busy?
Does your scripts take very long time to connect to the database?
Do you have lots of RAM, strong CPU, just a little traffic and despite that a very long database response time?
Are you seeing connections with “unauthenticated user” while running show processlist in MySQL console?
mysql> show processlist; +------+----------------------+-----------+----------+----------+------+-------+--------------+ | Id | User | Host | db | Command | Time | State | Info | +------+----------------------+-----------+----------+----------+------+-------+--------------+ | 2047 | unauthenticated user | localhost | myDB | Connect | 81 | | NULL | | 2049 | unauthenticated user | localhost | myDB | Connect | 81 | | NULL | | 2050 | unauthenticated user | localhost | myDB | Connect | 76 | | NULL | ... +------+----------------------+-----------+----------+----------+------+-------+--------------+ 131 rows in set (0.00 sec)
If you answered yes to any of the above questions your MySQL might have a problem with resolving connection’s host name.
When attempt is made for a new connection, MySQL tries to resolve the host name for that request. It takes the IP address and resolves it to a host name (using gethostbyaddr()). It then takes that host name and resolves it back to the IP address (using gethostbyname()) and compares to ensure it is the original IP address.
This might considerably increase connection time and slow down your whole application or produce show processlist result as above. You can easily solve this problem by disabling DNS host name lookups. In order to do this you need to run your mysqld with –skip-name-resolve option or add it to your my.cnf file like that:
[mysqld] skip-name-resolve
After that running show processlist will result in “Host” column displaying only IP addresses instead of host names and the connection speed should be much faster.
Just keep in mind that also you have to change allowed hosts for your database users to proper IP addresses.
hi Kosinski,
This is a nice post and it really helped me to solve a similar kind of issue what we faced in our prodcution system. Great work.
thanks,
Nellai…
Good website. I am going to require a bit of time to think over the info:D
I ran into this issue randomly. Editing /etc/my.cnf and adding “skip-name-resolve” did solve my problem. I still am not sure why it happened all of the sudden.
It was the same for me. One day just all of a sudden my MySQL slowed down considerably. Above was what fixed it for me.
Hi, this sounds as if it may by my problem BUT when I look in the event log I find that the MySQL user is attempting to connect to SQL Server Express.
Login failed for user ‘datamon’. [CLIENT: ]
datamon is the user on MySQL NOT SQL Server Express. Do both use localhost? Would it be possible to make this a named instance rather than localhost, or can I specify the port or something. (Sorry only my second day on MySQL)
You rock, man! Tnx for the advice!
you saved my lif
Thank you
Perfect post! thanks!
I had this problem also. Strange thing is that it was not always the case, probably depending on the load of the nameserver. Anyway my website is running fast as hell after applying the fix. (BTW setting the google nameservers instead of this tweak also fixed my site)
I’m glad my post was of help to you
Yes, just found your site with google. Great post, thanks!
thank you,
That’s fix my problem.
Hey,
It worked for me too.
thanks