How RSS and ATOM inform client about updates? long polling or polling or something else?

Question

I read that RSS and ATOM are HTTP-based using XML format. So how an RSS or Atom reader get informed about content updates if HTTP doesn't support connections? Do they need to poll the server periodically? I'm interested in using it in a real time web application but I heard that "polling doesn't scale".

Answer 1

This is pretty similar to this question. Please read my answer there.

There is no currently long polling for RSS feeds. The technology you're looking for is PubSubHubbub : it will allow the feed publisher to push you the content when it's available.