My Erlang Factory keynote also goes into the design considerations and PubSub layer optimizations that sits underneath Phoenix.Presence:
<a href="https://www.youtube.com/watch?v=XJ9ckqCMiKk&feature=youtu.be" rel="nofollow">https://www.youtube.com/watch?v=XJ9ckqCMiKk&feature=youtu.be</a>