Hello, I'd like to take up this Jira ticket <https://issues.apache.org/jira/browse/KAFKA-4680>. This is an old ticket, marked as a Kafka bug.
Before moving forward, I'd like to open a discussion on what would be the best approach to take on when doing the validation, as well as discuss about possible edge cases we should consider. Basically, at the moment, it is possible to specify min.insync.replicas > replication factor. When this happens, it is not possible to produce on a topic when acks=all as client callback returns NOT_ENOUGH_REPLICAS, and the broker logs error messages on each request. As suggested in the Jira, the validation should happen much earlier in the process, eg. at topic creation/configuration setup. Regarding the approach to use on validating the configuration; do we want, for instance, to: 1. print a WARN about the mismatch in the configuration 2. make the request FAIL 3. or print a more specific message on produce Options 1 and 2 anticipate the validation on topic creation / configuration change. These require to validate the configuration in more than one place: at topic creation, at configuration setup/update (both for min.insync.replicas and the default.replication.factor), at partition reassignment (when reducing replication factor). Don't know about consequences Option 3 is simpler; it does not anticipate the validation, but at least improves the visibility over the issue on the client side. I'd be in favor of a softer approach, which might include both printing a warning on topic creation/configuration-update and eventually a more specific message when producing on the topic. On the other end, this does not solve the problem, as we would allow anyway the mismatch in the configuration. Option 2 would solve the problem with an harder validation (eg blocking topic creation or configuration setup), but this requires to validate any possible edge case (eg. how do we prevent a change in min.insync.replicas if we have already created topic with lower replication factor?). Let me know what's your opinion on this, and if there is any other scenario we should consider for the validation (for instance, what's the impact on internal topics?). Thanks, Paolo
