[tylerchurch]

It's all about a persistent connection between the client and server, with the server pushing updates to the client as new data/events come in.

If you don't have a good async model, you're down to a thread/process per connection, which can get very expensive since you will have a thread for every user on your site.

You need something like Erlang's lightweight internal "processes", golang's coroutines, or maybe even Node.js evented I/O async model to handle this well.