Right, so this looks like it could create an issue similar to what's currently being discussed in https://issues.apache.org/jira/browse/KAFKA-1649 where users now get errors under conditions when they previously wouldn't. Old clients won't even know about the error code, so besides failing they won't even be able to log any meaningful error messages.
I think there are two options for compatibility: 1. An alternative change is to remove the ack > 1 code, but silently "upgrade" requests with acks > 1 to acks = -1. This isn't the same as other changes to behavior since the interaction between the client and server remains the same, no error codes change, etc. The client might just see some increased latency since the message might need to be replicated to more brokers than they requested. 2. Split this into two patches, one that bumps the protocol version on that message to include the new error code but maintains both old (now deprecated) and new behavior, then a second that would be applied in a later release that removes the old protocol + code for handling acks > 1. 2 is probably the right thing to do. If we specify the release when we'll remove the deprecated protocol at the time of deprecation it makes things a lot easier for people writing non-java clients and could give users better predictability (e.g. if clients are at most 1 major release behind brokers, they'll remain compatible but possibly use deprecated features). On Wed, Jan 14, 2015 at 3:51 PM, Gwen Shapira <gshap...@cloudera.com> wrote: > Hi Kafka Devs, > > We are working on KAFKA-1697 - remove code related to ack>1 on the > broker. Per Neha's suggestion, I'd like to give everyone a heads up on > what these changes mean. > > Once this patch is included, any produce requests that include > request.required.acks > 1 will result in an exception. This will be > InvalidRequiredAcks in new versions (0.8.3 and up, I assume) and > UnknownException in existing versions (sorry, but I can't add error > codes retroactively). > > This behavior is already enforced by 0.8.2 producers (sync and new), > but we expect impact on users with older producers that relied on acks > > 1 and external clients (i.e python, go, etc). > > Users who relied on acks > 1 are expected to switch to using acks = -1 > and a min.isr parameter than matches their user case. > > This change was discussed in the past in the context of KAFKA-1555 > (min.isr), but let us know if you have any questions or concerns > regarding this change. > > Gwen > -- Thanks, Ewen
