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Re: [rss-public] Re: Profile Section on TTL

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  • James Holderness
    I have some more info on ttl usage now. I haven t tested every aggregator in my collection, but I ve at least done all the ones currently listed in the profile
    Message 1 of 8 , May 31, 2007
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      I have some more info on ttl usage now. I haven't tested every aggregator in
      my collection, but I've at least done all the ones currently listed in the
      profile (except for MyYahoo! which can't subscribe to anything at my
      domain). I figure this should be enough to clarify the situation.

      For anyone that wants to double check my results, these are the test feeds I

      The first one is just a baseline test with no ttl to check the default
      refresh time. The second has a ttl of 15 to test whether aggregators would
      treat the ttl as the minimum refresh frequency. The last one has a ttl of
      150 to test whether aggregators would treat the ttl as the maximum refresh

      For the tests to work the aggregator's default refresh frequency needs to be
      greater than 15 and less than 150. For most this isn't a problem, but
      Internet Explorer uses 24 hours by default, Opera and Googler Reader use 3
      hours, and JetBrains Omea uses 4 hours. For IE and Omea I set the default
      refresh time to 60 before testing. For Opera I set the individual refresh
      times for each feed as I subscribed. For Google Reader I used a special test
      feed with a ttl of 210 (same as the urls above - just change the number on
      the end).

      All of the following aggregators appeared to ignore ttl completely. In other
      words, all feeds refreshed at the same default frequency.

      BlogBridge 4.0.1
      Bloglines 2007-05-31
      Google Reader 2007-05-31
      JetBrains Omea Reader 2.2
      NewsGator Online 2007-05-31

      The next lot of aggregators appeared to treat ttl as the maximum refresh
      frequency. The ttl150 feed would refresh every 150 minutes (180 in some
      cases, but never more frequently than 150). The ttl15 feed refreshed at the
      default frequency.

      BottomFeeder 4.2
      CITA RSS Aggregator 2.6
      IE 7.0.5730.11
      NewzCrawler 1.8.0
      Opera 9.02 (8585)
      Snarfer 0.8.0

      The odd one out was FeedDemon (both version and, which
      basically treated ttl as a recommended rate. When you subscribe to a feed,
      FeedDemon will set the refresh rate for that feed to the current ttl. So the
      ttl150 feed's initial refresh rate was set to 150 minutes; the ttl15 rate
      was set to 15. Those values could be overridden though - they didn't
      actually limit the refresh rate in any way.

      It's also worth noting that the ttl15 feed only actually refreshed every 30
      minutes, despite being set to 15. I'm not sure if that is a limit of the
      FeedDemon trial version, a bug, or there's some other reason for it.

      Some other things you should know if you want to run these tests yourself.
      GreatNews will sometimes force a refresh just by clicking on a feed to view
      the results, so it's best to leave it alone for a day while the results
      accumulate. Some aggregators (especially the online ones) will behave
      unpredictably for the first refresh or two - sometimes they'll refresh
      sooner than expected, sometimes later. Once again, it's best to leave them
      for a day and let the results accumulate.

      The tests rely on an aggregator supporting etags, or archiving results so
      you can see a history of all the refreshes that have happened. There are
      some that can do neither. These tests won't work very well for such

      Bottom line: it seems most aggregators either ignore ttl or treat it as the
      maximum refresh frequency (i.e. the aggregator won't refresh more often than
      specified). We have one aggregator that is known to treat ttl as a
      recommended refresh frequency. We still do not know of any that treat it as
      a minimum refresh frequency.

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