Hello,
I am not sure if I can already be helpful since I am new to the environment but I have some strange findings in the monitoring graphs.
First I'd be interested in the MySQL host you ask. Then: this is the graph. http://munin.toolserver.org/Database/rosemary/mysql_bytes.html Rosemary (one of the enwiki-DB-Hosts) seems to bring the maximum of the I/O that is possible, disk graphs are clipping there. In the MySQL traffic graph you can see there is clipping too. Strange thing about this is that this phenomenon started in the middle of september. Can anyone remember any important change in this time? That is not the case with thyme (other enwiki DB Host) so it'd be a question wether we could share the load better. Also I enabled query caching and will see if this is useful in any way.
Another question would be: which queries are especially slow? Do you have special trouble with joins?
Cheers nosy