Have you tried to join a crowded room on Matrix on a young server where you are the first to do so ? It's... slow. It will manage eventually but you can make your favorite beverage in the meantime.

Hopefully the Matrix and Synapse people has been at work this year to substantially improve that, and this talk will present you the details about it. Our journey will begin with presenting the needed specs changes, and then go through the various implementation foot-guns that we had to dodge.