I've got a website (Wordpress based) that became unresponsive. I SSH'd into the server and saw that we were out of memory. Errors in my apache log files indicated the same... things failing to be allocated due to lack of memory). Restarting the server fixes it.

So I look in access.log and error.log around the time of the incident but I see nothing strange. No extra traffic, no unusual requests. In fact the only request around the time of the problem was one from Googlebot for an rss feed... at that point I start to see 500 response codes in the logs until the machine was rebooted. I look in message.log hoping to see something but there is nothing at all for that entire day (which is odd as there are entries for every other day).

The site has a large amount of memory allocated to it and normally runs using about 30% of what is available. My question... how would you go about trying to track this down at this point? What are some other log files I could check or strategies I could take?