Too many sessions logs users out

[vortexhlp]

Hi everyone, I wanted to ask a simple question in regards to sessions.

PHPBB 3.0.8
Problem exists with default settings, but currently using 40+ mods
Using php 5.3.18 (cli), MySQL 5.0.95 / CentOS 5.9 (Final)
What happens?
Blame it on spambots or a buttload of people coming to my website, once there's around 2000 sessions in the database, people just start getting logged out after signing in. I'm not sure why, but this is always the case. I went on vacation for a month and there were over 500,000 sessions in the table.

I think maybe the solution is to have an automated task that purges the sessions every few hours or so. phpbb doesn't seem to do it on its own and clearing the cache from ADM doesn't help. In fact, what does clearing the cache do? Does it just delete the cached files in the /cache folder? I don't know how to create such a task or even know if this would resolve the situation. But once i do clear the cache it's gone. Why is this?

Anyways, thank you for your time!

[Oyabun1]

phpBB already trims the sessions table. If yours has 500,000 seesions then maybe the standard code has been broken by one of 40+ MODs.

Please fill out the Support Request Template Generator and post it back here to enable us to assist you better. Also what are your settings for
ACP > GENERAL > Load settings > Session length
and
ACP > GENERAL > Security settings > Allow persistent logins