how to count the number of online users [duplicate]

Possible Duplicate:

Who's Online in Pylons

We have a project on the pylons. And now the task is to count all users are on the site. Do this with a session does not work, because the lifetime of the session for about a day. How can I do?

In my project (but in django), I'm store user id in database with time of last request and show all users for last 5 minute.