If you're keeping all data of all sessions in one container, you need something as reliable as a database (including locking, crash recovery, backups, etc.) -- MySQL, PostgreSQL, even SQLite come to mind.

Not sure how long you need to keep the session data around, but one different approach would be using Cache::File -- that's usually a great way to manage session data, using the session key as index, it'll use a different file for every session.