[mod_python] Session Query

Hello friends,
i am using Session.Session(req) function in mod-python for session handling
it has created a mp_sess.dbm file in /tmp folder its size is increasing 
and is currently 500 MB.
What is the problem and what is actually happening internally with 
Session utility and what is the problem and what do i have to do
to avoid this.
And is the performance being affected due to this file
Please reply .
Thanks in advance.
Regards,
Ajinkya