Site/Server crashed under load testing

Hopefully someone can help me determine how to troubleshoot my server crashing.

I’m running wordpress multisite. I started using a load testing website to see how my site would perform. I tested with a minimal 15 users and the site bit the dust.

I need help determining where/what the culprit of the crash is. I’m running many wordpress plugins, of those I’m running W3 total cache which should be helping my site not crash. :confused:

I’ve looked at my Apache error logs, but they’re not very helpful. The main error that I notice when I run the load test is this: [warn] mod_fcgid: read data timeout in 31 seconds
[Sun Feb 27 01:08:34 2011] [error] [client] Premature end of script headers: index.php.

I’m on a Linode VPS with 512mb of RAM. If I look at the graphs in linode I can cleary see where the CPU (200%) and Disk IO (19000) spike.

Where should I start?


The mod_fcgid timeout may just have been due to your server having a high load at the time…

That said, you could always try switching to mod_php as your PHP execution mode rather than FCGID, to see if you get better performance. You can do that in Server Configuration -> Website Options -> PHP Execution mode.

It sounds like you’re seeing a pretty huge load though – the load testing may have simply generated more load than your application, or server, are able to handle.

You may want to turn down how many processes Apache can spin up – otherwise, with only 512MB of RAM, it wouldn’t take long to eat through your available RAM. You can do that by tweaking the MaxClients settings in the Apache config.