We have a VPS server (it's using Virtuozzo). On a few occasions now, our VPS memory was fully used up and no new connections could be made to the server on SSH, SMTP, or POP. The only thing that works is connecting to the web service. Luckily, plesk is running on the VPS and we have been able to reboot it through plesk (as well as see that the RAM is 100% used).
I would like to find what process is causing this. I have a feeling it's MySQL, but don't really know. Is there some sort of logging I could implement that would help me find out what was the cause of this next time it happens?