Mentioned in internal doc about speeding up /messages. Also see "2. Loading tons of events" in #13356

get_bundled_aggregations takes a few seconds even when there is no relations. This happens at the end of every /messages request.

For 500 messages that have 0 relations, reactions, threads, redactions, it takes 1 second to process. This is reproduced by running the many users, many messages Complement test I have in matrix-org/complement#443

Bunch of get_annotations_for_event and get_relations_for_event calls for each message:

Potential solutions

Batch up the lookups. It looks like most are just the magnitude of the round-trip to and from the database for each of the messages.