Hello, I just want to summarize where we are in this discussion
There are two major points of contention: should we have acks=1 or acsk=all by default? and how to cap max.in.flight.requests.per.connection? 1) acks=1 vs acks=all1 Here are the tradeoffs of each: If you have replication-factor=N, your data is resilient N-1 to disk failures. For N>1, here is the tradeoff between acks=1 and acks=all. With proposed defaults and acks=all, the stock Kafka producer and the default broker settings would guarantee that ack'd messages would be in the log exactly once. With the proposed defaults and acks=1, the stock Kafka producer and the default broker settings would guarantee that 'retained ack'd messages would be in the log exactly once. But all ack'd messages may not be retained'. If you leave replication-factor=1, acks=1 and acks=all have identical semantics and performance, but you are resilient to 0 disk failures. I think the measured cost (again the performance details are in the wiki) of acks=all is well worth the much clearer semantics. What does the rest of the community think? 2) capping max.in.flight at 5 when idempotence is enabled. We need to limit the max.in.flight for the broker to de-duplicate messages properly. The limitation would only apply when idempotence is enabled. The shared numbers show that when the client-broker latency is low, there is no performance gain for max.inflight > 2. Further, it is highly debatable that max.in.flight=500 is significantly better than max.in.flight=5 for a really high latency client-broker link, and so far there are no hard numbers one way or another. However, assuming that max.in.flight=500 is significantly better than max.inflight=5 in some niche use case, the user would have to sacrifice idempotence for throughput. In this extreme corner case, I think it is an acceptable tradeoff. What does the community think? Thanks, Apurva
