Session problem

Hello all each user gets a session id which can be reused later. I am writing all encoded details to for that session to mysql database. If the same user returns later (hours,day) he/she can use her Id (input box) and I get the details from the database. I did notice that the session id is also written to the /tmp folder. Linux mandrake. Things go wrong when I delete the session id in the /tmp folder. It should not be there in the first place I think, as all details of that session should be written to the db. Does somebody know how to fix this?