session garbage collector

[eluser]WanWizard[/eluser]
NDB sessions use the standard PHP session as backend.

Apart from possible security issues (all web apps on the same host can access those session files), the garbage collection process for session files works exactly the same as CI's GC process for DB sessions. So what have you solved now?

You could have read the manual as well, which tells you you can control the GC process by increasing the GC probability. If you set this to 100%, it always runs, and removes expired session records on every load of the session library. If that is desired is up to you.