session store garbage collection

[evanp]

I'm trying to implement session storage using the databank library (https://github.com/evanp/databank), and as far as I can tell old sessions are only cleaned up if there's a get() request for an expired session.

A periodic process to GC sessions would help keep storage requirements reasonable.

[tj]

the GC portion is completely adhoc, redis happens to expire for you, others might require some manual queries etc. Do whatever you need to do and provide an option via the store's constructor, or you can check on GET as an alternative