A social data aggregator generates entries of action data describing actions taken by users of a social networking system. The entries are archived in a number of remote data hosts, with a portion of the entries stored in an action cache to expedite retrieval. The action cache is modified to include relevant entries of action data by selecting the most relevant entries from proxy data aggregators, which identify sets of entries from remote data hosts coupled to the proxy data aggregators based on the relevance of the entries in the remote data hosts. The relevance of an entry is based on an associated engagement score indicating a likelihood of a user requesting content interacting with a notification based on an entry.