[KAFKA-8695] Metrics UnderReplicated and UnderMinIsr are diverging when configuration is inconsistent

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Duplicate
• Affects Version/s: 2.1.0, 2.2.0, 2.1.1, 2.3.0
• Component/s: core
• Assignee: Alexandre Dupriez
• Reporter: Alexandre Dupriez
• Created: 22/Jul/19 15:08
• Updated: 14/Aug/19 06:03
• Resolved: 14/Aug/19 06:03

Description

As of now, 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 consequence, 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.

 

Issue Links

• duplicates: KAFKA-4680 min.insync.replicas can be set higher than replication factor