Re: FN-FORUM: Help! Apache server being hammered and site keeps falling over!

date posted 1st November 2007 10:12

> This takes time and money, though; this is more about quick speed
> fixes, something which the config posted previously seems to have
> helped with.

My guess is a slow MySQL query: when I get these during development (such
as with huge tables and forgetting an important join condition, so the
results go silly) it effectively hangs the MySQL and apache processes,
leading to excessive CPU and load. Re-starting MySQL kills the run-away
query, and all returns to normal.

> I'm guessing there's a fairly major memory leak somewhere in the
> software, but I'm not sure where it is.

You have plenty of spare memory and no swapping, so it's not a memory
problem. It's a CPU usage problem: something is doing rather too much
calculation work. That could be an inefficient PHP script or an
inefficient MySQL query.

mod_status will tell you which web pages are taking the CPU, which should
help you narrow down the problem.

And you do have indexes on all your foreign keys in MySQL, don't you?
Miss one on a large table and your query can quickly go from taking a few
milliseconds to dozens of seconds.

Anthony
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