On Tue, Jan 17, 2017 at 6:17 PM, Apurva Mehta <apu...@confluent.io> wrote:
> Hi Jun, > > Some answers in line. > > > 109. Could you describe when Producer.send() will receive an Unrecognized > > MessageException? > > > This exception will be thrown if the producer sends a sequence number > which is greater than the sequence number expected by the broker (ie. more > than 1 greater than the previously sent sequence number). This can happen > in two cases: > > a) If there is a bug in the producer where sequence numbers are > incremented more than once per message. So the producer itself will send > messages with gaps in sequence numbers. > b) The broker somehow lost a previous message. In a cluster configured for > durability (ie. no unclean leader elections, replication factor of 3, > min.isr of 2, acks=all, etc.), this should not happened. > > So realistically, this exception will only be thrown in clusters > configured for high availability where brokers could lose messages. > > Becket raised the question if we should throw this exception at all in > case b: it indicates a problem with a previously sent message and hence the > semantics are counter intuitive. We are still discussing this point, and > suggestions are most welcome! > > I updated the KIP wiki to clarify when this exception will be raised. First of all, I renamed this to OutOfOrderSequenceException. Based on Jay's suggestion, this is a more precise name that is easier to understand. Secondly, I updated the proposed API so that the send call will never raise this exception directly. Instead this exception will be returned in the future or passed with the callback, if any. Further, since this is a fatal exception, any _future_ invocations of send() or other data generating methods in the producer will raise an IllegalStateException. I think this makes the semantics clearer and addresses the feedback on this part of the API update. Thanks, Apurva
