Faster joins: audit code paths that do state queries

[richvdh]

Check that all the code paths that do state queries are happy with partial state. There are a bunch of things that call get_filtered_current_state_ids which really aren’t; there may well be others.

[erikjohnston]

What do people think of indirecting all calls to DataStore.get_current_state_ids and co via the StateStorage, and then updating PartialStateEventsTracker to also track current state?

The downside to this approach is that it'll be easy for people to muscle memory using store.get_current_state_ids() and so bypassing the checks. That is true of the equivalent state group functions today I guess

[richvdh]

To summarise what was said in chat:

• when erik says StateStorage, he means StateGroupStorage.
• PartialStateEventsTracker feels like the wrong place (better put it in a separate class)
• indirecting current_state etc through StateGroupStorage (and renaming it to StateStorage) seems sensible.

[erikjohnston]

#12872 and #12964 will have sorted out a bunch of places that we check current_state_events, but someone should go through and audit if there are any other queries

[richvdh]

I've been through the things that call methods in StateGroupWorkerStore and RoomMemberWorkerStore and opened a few issues, but mostly it's just "presence and device lists are going to be a nightmare", and they are covered by #13008 and #12993 respectively. I don't think further staring is going to be particularly fruitful and instead we should just file new issues as we find them.