observer(subscriber) Design Pattern on Web?

Question

I'm been trying to get caught up on web 2.0 practices, and recently ran into a article about polling for changes in a database to keep a webpage up to date asynchronously (for a purpose similar to the way stack overflow tells you when a new answer has been added).

This got me thinking if it was possible to implement an subscribe/update relationship on the web. Does anyone know if this is possible and if so can maybe link to a good article about it?

Also does anyone know how stack overflow implements their async update system? Polling seems very inefficiency for a site with as much traffic as stackoverflow.

Answer 1

There are currently no other solutions than polling and WebSockets that has sufficient browser support. Stack Overflow implements this with a technique called long polling, described here:

WebSockets vs Server-Sent Events vs Long-polling