RSS: Time to Live (TTL)
I recently fielded a question on the ROME users list about using ttl for RSS 2.0, and it touches on something I have had to research for an upcoming O’Reilly piece….
ttl (Time to Live) is an element in RSS 2.0 that is intended to inform aggregators “how long a channel can be cached before refreshing” the feed.
Some people interpret this as a minimum poll time. Others interpret this as a maximum poll time. Some people think that you should use ttl + pubDate to determine how long content should be displayed. (Time to live, after all, implies the content literally expires.)
The RSS Advisory Board has had recent conversations on the spotty support for ttl among RSS readers…. It appears that half of the big aggregators don’t support it, and the other half don’t all use ttl the same way. For example, Sean Lyndersay (Microsoft) says this about IE7: “IE7’s default update schedule is 24 hours. If you set ttl lower than 24 hours, then the default update schedule will take precedence because it is higher.”
These are the informal findings of people on the public forums for the RSS Advisory Board:
Don’t support
ttl:
Bloglines, FeedDemon, NewsGator Online, My Yahoo, Firefox 1.5Support
ttl, but not necessarily the same way:
BottomFeeder, GreatNews, IE7, NewzCrawler, Snarfer, Opera 9
The moral of the story, at least from my perspective, is that ttl’s usefulness is limited; for the moment don’t count on it being used the way you intend.
If you think one of the aggregators above is incorrectly listed, or have others to add, feel free to comment accordingly.
August 31st, 2006 at 17:08
Let me stress that TTL does work, but only with half the clients. But it does work. So, if you want your RSS to be more real-time, you can set the TTL to 5 minutes and for many clients, you’ll be the freshess feed. If you are getting killed with bandwidth, you can set the TTL to 24 hours and this will reduce bandwidth, just not as much as it should. It’s not perfect. But it does work.
August 31st, 2006 at 22:10
Randy and I continue the conversation here: http://groups.yahoo.com/group/rss-public/message/882
September 6th, 2006 at 04:15
Randy: properly supporting If-Modified-Since and Cache-Control headers should generally have the same effect. The best thing is, most bloggers don’t usually have to do anything to support ‘em.