No, that's up to you, when you construct sess_id from user name, time or such stuff...
I'v never wrote that I don't use CPAN, and if you want, you can see my preference of short own code rather than some module stupid, I see the same as independancy.
The probability of collisions when my id's are generated is, I know, but it is theoretical when more than 10 character length used. But if you check it against sessions in db when created, your action is the same as when checking the same session id given from the next request of the logged user. I cannot see relevant slowdown...
I know that I am not perfect and my solutions really contains bugs, but somebody can be interested in.