I have a PHP website which uses $_SESSION variables. It runs on Apache, Mysql and Ubuntu 14.04 on a very resourceful server (Amazon EC2 - M3.X-large)
For some unknown reason, the website virtually grinds to a halt every so often, and I don't know why. When this occurs, very few people are visiting the website, and server load is very low. Restarting Apache & MySQL does nothing, however, after about an hour the website speed returns to normal. Restarting my entire server also temporarily fixes the problem, but after a few days the problem reoccurs.
My question is - what could be causing this problem, and what can I do to debug / fix it? Like I said - traffic is very low when the problem occurs so I don't think apache / php require more resources. I think the problem runs deeper. Could the amount of session data being saved be causing the issue?
Thanks in advance.