I've got a mediawiki instance that seems to randomly log people out. Sometimes it takes hours, sometimes seconds. I haven't figured out what's triggering the logout, but it doesn't seem to be a session timeout. What php/mediawiki settings should I look at?
Since Memcache is not an option, and I'm assuming that using tmp file storage is just as error prone in your shared hosting environment, your only route is to tell PHP to store the session data in MySQL (and once your server load can't accommodate this you'll then be able to move to hosting where you can use Memcache.) Two good articles on the topic for using MySQL to store PHP's sessions are http://www.tonymarston.net/php-mysql/session-handler.html and http://shiflett.org/articles/storing-sessions-in-a-database (though they are dated, they are still correct.)