This is the same call that is done in access-scoped general search. The performance tests were designed to hammer this call and draw out its impact, and it wasn't terrible.

The `tr_tx_general_search_search` is the one that hits this when: a) the user session is authenticated; b) the search includes content or groups (pretty much all for case b, I think). The transaction gets 135.6 req/s (more than any other) in the weighted searches.

We could investigate the impact of using Redis as the Memberships cache instead of Cassandra.