Hi all,

I have a CentOS 5.6 xen domU that is used for hosting several Apache virtual hosts that use MySQL.

Lately, this domU has been having performance issues and I've noticed web pages loaded from this server opening slower than usual.

When I run 'top' I see mysqld constantly consuming 10-60% of CPU.

sar reports average of 10-20 for %user, 5 for %system, 0.2 for %iowait and 10-20 for %steal

When looking at 'xm top' in dom0 (running also CentOS 5.6) most of the other domUs have CPU(%) near zero and only this domU is reported to consume CPU more than 10%.

The strange thing is, that when I run 'mytop', I do not see that many queries: I see avg of 4 users "sleeping" and occasionally some other user running a query. qps is mostly 0. No slow queries. Key efficiency is 97%.

Here is my /etc/my.cnf:

max_connections = 300 max_user_connections = 300 wait_timeout = 180

Nothing interesting in /var/log/mysqld.log. I tried rebooting both the dom0 and the domU which made no difference.

Questions:

1. How to debug further why mysqld is taking so much cpu?

2. If I've understood correctly, the high steal% value reported by sar means that the hypervisor is giving cpu time for some other domU. How to find out why and where this cpu time is stolen to?

Regards, Peter