Hello Community, I noticed Kafka allows the replication factor of a topic and "min.insync.replicas" to be set such that "min.insync.replicas" > the topic's replication factor.
As a consequences, the JMX beans kafka.cluster:type=Partition,name=UnderReplicated and kafka.cluster:type=Partition,name=UnderMinIsr can report diverging views on the replication for a topic. The former can report no under replicated partition, while the second will report under in-sync replicas. Even worse, consumption of topics which exhibit this behaviour seems to fail, the Kafka broker throwing a NotEnoughReplicasException. [2019-07-22 10:44:29,913] ERROR [ReplicaManager broker=0] Error processing > append operation on partition __consumer_offsets-0 > (kafka.server.ReplicaManager) > org.apache.kafka.common.errors.NotEnoughReplicasException: The size of the > current ISR Set(0) is insufficient to satisfy the min.isr requirement of 2 > for partition __consumer_offsets-0 In order to avoid this scenario, one possibility would be to check the values of "min.insync.replicas" and "default.replication.factor" when the broker starts, and "min.insync.replicas" and the replication factor given to a topic at creation time, and refuses to create the topic if those are inconsistently set. This was reproduced with Kafka 2.1.0, 2.2.0 and 2.3.0. What do you think? Alexandre
