massive storm of presence EDUs when joining a large room

[richvdh]

after you do your send_join to a room, all the servers in the room seem to immediately send you presence updates. Since this will often be the first contact you get from those servers, we then end up doing hundreds of server key requests, all of which end up starving out the actual join request - contribuiting to the join itself taking ages.

[richvdh]

possibly related to #2514

[ara4n]

dup #3962?

[richvdh]

dup #3962?

I don't think so. #3962 is about presence updates that we don't expect. AFAICT the EDUs referred to in this issue are expected - the problem is just that there are a lot of them, and they all arrive during the join dance and tend to block it.