Software for an online social service receives a request for a newsfeed from a user. The newsfeed depends at least in part on a memory-cached list of social friends of the user and on a memory-cached list of events associated with each social friend. The software refreshes a memory-cached copy of the list of social friends from a corresponding list in a persistent data store, based upon a determination of a utility associated with the user. And the software refreshes a memory-cached copy of a list of events associated with a social friend from a corresponding list of events in a persistent data store, based upon a determination of a utility associated with the social friend. Then the software causes the newsfeed to be displayed to the user.