Lately, we have been receiving reports of the appearances of duplicate articles of previously read items. Ironically, this is due to a code change we have made to prevent the possibility of duplication in the future. Feeds do not always publish articles in a consistent order. Often times, they publish older items on their RSS feeds. When this happens, we need a way to prevent these duplicates from appearing in the reader. In order to do this, we need to cache some identifying information about the articles processed, so that we can cross check new articles with previously processed ones. If a newly grabbed article matches a previously processed one, we won't allow it to be reprocessed. However, we need to allow identifiers to expire after set amount of time or the cache will grow indefinitely, we chose 7 days because it worked well with our cache size.
Every time a feed is processed we update the expiration date on articles that are still in the feed and in theory this would prevent the possibility of duplication under normal circumstances. Of course, nothing is that simple, and this is where Etags and last modified come in. Etags and last modified are bits of information that are used on websites to let you know if anything has changed since the last time you downloaded it. At Aol/Reader we use etags and last modified to save publishers bandwidth and us processing. When a publisher publishes infrequently (greater than 7days) and they provide us etags/last modified there is a possibility that articles could expire from the cache before a feed is reprocessed. This (on rare occasions) could cause duplicates. To address this we are taking several steps, the first of which is to add a lifetime to our etags/last modified that is shorter than our cache expiration. The unfortunate side affect of this is that all feeds that have had no updates in the last 7 days will duplicate the current articles in their feeds exactly once. The good news is that it is far less likely that articles will duplicate in the future. Thanks for bearing with us while we make Aol Reader even better.
We've just released this patch, so you should no longer see this happening, unless the feed is not updated within the week, as stated previously. We have also fixed a couple of bugs since the previous update:
- We have fixed the loading issue. You should no longer have trouble with loading the reader.
- When in full view, you were unable to use the n/p shortcuts unless you first scrolled. You can no use them freely.
If you continue to see any of these problems feel free to contact us at help.reader.aol.com