On Fri, Jun 8, 2012 at 8:07 AM, gramanero <graman...@gmail.com> wrote: > > If I let the transaction rollback, then I have the message on the queue > still and then run the risk of trying to process it a second time which > will result in the same scenario and most likely end up in an endless loop. > Unless I configure the redelivery policy to only attempt to redeliver N > times as opposed to an infinite numer of times. >
With the "purgatory" pattern (best name I could think of at the time), the transaction is allowed to rollback, but the message is "blacklisted" and it sort of "bounces" back off the front of the queue. The next time the consumer grabs the message off the queue, it recognizes that it has been blacklisted and it forwards it to the purgatory queue (unless it has already been there too many times, then it goes to the DLC queue) to sort of take a "time out." There is a throttled (to keep it from thrashing) consumer on the purgatory queue that inspects each message that comes off the queue. If the message has fulfilled its timeout and it's ready to try to come back and play nice, then it sends it back to where it came from (the original input queue). If not, then it just puts it back on the purgatory queue (hence the possibility of thrashing) to be processed again in a bit. Again, at some point (hopefully today), I hope to implement a feature which would allow the original input route (which consumes from the input queue) to detect (still working on the algorithm) when it is sending too much stuff to purgatory or DLC. When that happens, it will spin off a thread to suspend it's consumer. It will also schedule a timer task to come back and wake it up in a bit when hopefully the problem (database down, web service unavailable, etc.) has been addressed and everything is happy again. The input queue itself will still continue to function and receive messages. The consumer just won't be pulling messages off the front for a little while. The one requirement we have that this does address is that messages are definitely not lost, since all of the routes are transactional.
