My ci_sessions table is empty?

CI 2. There is no config['sess_driver'], I have $config['sess_use_database'] = TRUE;

Well my question is - am I supposed to set session data in the database or CI does it automatically?

Do the one thing you think you cannot do. Fail at it. Try again. Do better the second time. The only people who never tumble are those who never mount the high wire.