PubSubHubbub (also known as PuSH) provides a way for services to subscribe to new entries in feeds (RSS & Atom) when they are published. This allows for new content to be distributed in a rapid fashion and reduces the need to regularly poll feeds to check for new content.
To subscribe to updates you must sent a request to a hub. The information about the hub is included in the feed itself, using an
atom:link tag with a
rel='hub' attribute. Here’s an example, the entry from the feed for http://en.blog.wordpress.com/
<atom:link rel='hub' href='http://en.blog.wordpress.com/?pushpress=hub'/>
The href attribute is the URL used when sending in a subscription request. The details of making a subscription request are covered in the PuSH specification, section 6.1. Subscriber Sends Subscription Request.
When you publish a new post WordPress.com gathers up the lists of PuSH subscribers for the feed and sends out the new content to them directly. Because the content of the new post is sent directly to the subscriber they aren’t required to fetch a copy of the feed to get the new data.
Frequently Asked Questions
How do I enable this for my WordPress.com blog?
It already is! Every site hosted on WordPress.com includes supports for PubSubHubbub.
How long does it take from the time I hit the publish button until the notifications get sent out?
Our observations have been that they go out with in a second or two.
Also see rssCloud.