The Simple Update Protocol is one of the very first protocols that was built to help feed polling. It makes it easy to find the most appropriate time to fetch a feed.
Created by the FriendFeed team, the idea is, for a publisher, to keep track of all the feeds that have been updated in a sup file. Then, a subscriber instead of querying the feed over and over again, just have to query this sup file. If a poller is just polling one feed, that’s not better, but if you’re tracking 1000 feeds, instead of polling them all, you just need to poll that specific SUP file.
One of the issues is that it’s not immediate, these SUP feed have a “period” and contain all the feeds that have been updated in that given period. The standard is 60sec though, so it shouldn’t be too “late”! Another issue is that these SUP can contain a LOT of feeds, so if you don’t have an very fast and efficient way to compare all the entries in this file to see if you’re actually tracking a specific feed, it may be quite “complex” to be sure to get all the updates.
Anyway, I have no idea why I’m telling you this, because, as a matter of fact, you don’t need to implement SUP, because Superfeedr does it for you. Give us a SUP enabled feed (from BackType, Disqus, Friendfeed, 12seconds.tv… etc), and we’ll fetch the right SUP file and you’ll get your content in a “close to real-time” fashion, via PubSubHubbub or XMPP, exactly like we did for RSSCloud!