I think I suggested to Brett in person at some point that the hub could use a per-subscription or per-feed counter that subscribers could keep track of. If the hub fails to send a message (or multiple messages) to the subscriber, but one eventually does get through, then the subscriber would be able to detect the message loss.
For example: Hub sends Message 1, Counter 1, subscriber receives it, sets Counter = 1. Hub sends Message 2, Counter 2, subscriber receives it, sets Counter = 2. Hub fails to send Message 3, Counter 3. Hub sends Message 4, Counter 4, subscriber receives it, detects that 2+1 != 4, goes back to feed to find the missing message., sets Counter = 4. Hub manages to re-send Message 3, Counter 3, subscribe receives it, notes that 3 < 4, does not reset counter[1]. Obviously, this does not help in the case where you're just not receiving any messages at all. I think the only way you can fix that is a low-frequency poll; if the hub has counters, it could be as simple as querying the hub for the current counter value, rather than going to the feed and trying to find new entries. In the case where a single feed notification is being sent, Section 7.1 of the spec could be updated to include the parameter "hub.counter"; for multiple feed notifications it might be more difficult to do, since the hub.url parameter is simply repeated, and there's no way to guarantee ordering. [1] If the hub would prefer to not have to maintain any sorts of guarantees that the counter will always increment, the spec could dictate that if the counter is less than a previously-recieved value, it should make a request to the hub to find the current counter value. Thoughts? b. 2010/1/8 noriguard <[email protected]>: > Hi, smart guys :-) > > I have get notifications for some blogs, but recently I recognized a > little loss of notifications. > (For example, yesterday, for a blog, 1 posts was not notified, while > other 4 posts are notified.) > I already checked my server but I cannot find any problematic setting > in my server, including max apache connection etc. > > My question is... > Is it possible that a hub (such as pubsubhubbub.appspot.com) does not > give all the notifications to every subscriber? > > If the answer is YES, I want to know how to minimize loss of such > kind, and/or when PubSubHubbub will be completely stabilized. > If the answer is ABSOLUTELY NO, I need to review all the setting in my > server again. :-( > > Thank you in advance. > > Happy new year! >
