session behavior

[eluser]WanWizard[/eluser]
The session cookie is updated every time you call $this->session->sess_write(), which happens automatically every time you call a session method that updates a session variable.
If you don't do that, the cookie also gets updated every call to sess_update(), which rotates the session_id. This happens once every 'sess_time_to_update' seconds.

So basically it's an inactivity timer.