I've been watching our mysqld procs in htop and the root thread is
using 75-100% of a CPU most of the time. I'm trying to understand
what that is being used for, and so I was hoping someone could tell me
what that thread does that might be using a lot of CPU.
We are using 5.5.4-m3, we use MyISAM tables with full text indexes, do
around 1500-2000 queries per second, accept around 150 connections per
second, and at the moment both our key cache and our query cache are
disabled (I was curious if that contention was an issue). CPU usage
didn't really change with the caches disabled.
The server is doing around 2 megabytes of traffic per second. We
store a bunch of data compressed, and use "uncompress(columnName)" in
queries to get it back out. None of these things set off any red
flags for me, but it has been a number of years since I've tuned
MySQL, so I don't really trust myself.