you don't need to keep their entire history in ram, you only need to keep their check-in history of places that they are on the verge of becoming mayors to in r

you don't need to keep their entire history in ram, you only need to keep their check-in history of places that they are on the verge of becoming mayors to in ram, (you are one day away from becoming mayor of xyz) and that you can calculate offline, and all you need to do is see if onedayaway:xyz:user_id => true on checkins, which you can keep in memcache