I can see it being a performance issue if you need to fsync session updates to disk constantly, but personally I'd be pretty much happy if the session was only

I can see it being a performance issue if you need to fsync session updates to disk constantly, but personally I'd be pretty much happy if the session was only saved at normal shutdown. Maybe saving it after a certain idle period would also be useful. Would that mitigate your performance concerns, or did I not guess the source of the issue correctly?