Hi Hopefully this is the correct email address and forum for this. I asked this question on stack overflow, but did not get an answer: https://stackoverflow.com/questions/50689177/kafka-ack-all-and-min-isr
*Summary* The docs and code comments for Kafka suggest that when the producer setting acks is set to allthen an ack will only be sent to the producer when *all in-sync replicas have caught up*, but the code (Partition.Scala, checkEnoughReplicasReachOffset) seems to suggest that the ack is sent as soon as *min in-sync replicas have caught up*. *Details* The kafka docs have this: acks=all This means the leader will wait for the full set of in-sync replicas to acknowledge the record. source <https://kafka.apache.org/documentation/> Also, looking at the Kafka source code - partition.scala checkEnoughReplicasReachOffset() has the following comment (emphasis mine): Note that this method will only be called if requiredAcks = -1 and we are waiting for *all replicas*in ISR to be fully caught up to the (local) leader's offset corresponding to this produce request before we acknowledge the produce request. Finally, this answer <https://stackoverflow.com/a/45783921/746754> on Stack Overflow (emphasis mine again) Also the min in-sync replica setting specifies the minimum number of replicas that need to be in-sync for the partition to remain available for writes. When a producer specifies ack (-1 / all config) it will still wait for acks from *all in sync replicas* at that moment (independent of the setting for min in-sync replicas). But when I look at the code in Partition.Scala (note minIsr < curInSyncReplicas.size): def checkEnoughReplicasReachOffset(requiredOffset: Long): (Boolean, Errors) = { ... val minIsr = leaderReplica.log.get.config.minInSyncReplicas if (leaderReplica.highWatermark.messageOffset >= requiredOffset) { if (minIsr <= curInSyncReplicas.size) (true, Errors.NONE) The code that calls this returns the ack: if (error != Errors.NONE || hasEnough) { status.acksPending = false status.responseStatus.error = error } So, the code looks like it returns an ack as soon as the in-sync replica set are greater than min in-sync replicas. However, the documentation and comments suggest that the ack is only sent once all in-sync replicas have caught up. What am I missing? At the very least, the comment above checkEnoughReplicasReachOffset looks like it should be changed. Regards, Carl
