I always seem to be having trouble with MySQL. For months i have gotten a lot of “Got timeout reading communication packets” and the aborted_connects value is very high. I can’t get to the bottom of this problem because this error occurs immediately and intermittently, and i never have time to SHOW PROCESSLIST to see what is causing it, because it only occurs for a split second - this problem causes PHP mysql_connect() to fail immediately, and when this happens i die() the entire page so users see a white screen (which is better than a whole lot of empty boxes, i guess).
Other than this annoying problem, the performance is very good. On average i do 198 queries per second and the site runs well. I have a suspicion the problem is caused by a query locking out the rest of the queries. But i can never tell.
When i examine my slow query log, i see simple UPDATE queries taking 5 seconds. I have low_priority_updates=1 - is this the reason they appear in the slow query log?
When i examine slow SELECT statements, i get conflicting results. One SELECT query took 5 seconds in the slow query log but when i executed it myself it took 0.0004 seconds. When i alter the query slightly to make it unique (to avoid taking results from the query cache), it takes 0.0006 seconds.