Metrics UnderReplicated and UnderMinSir are diverging when configuration is inconsistent

[Alexandre Dupriez]

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

[jira] [Created] (KAFKA-8695) Metrics UnderReplicated and UnderMinSir are diverging when configuration is inconsistent

[Alexandre Dupriez (JIRA)]

Alexandre Dupriez created KAFKA-8695:


 Summary: Metrics UnderReplicated and UnderMinSir are diverging 
when configuration is inconsistent
 Key: KAFKA-8695
 URL: https://issues.apache.org/jira/browse/KAFKA-8695
 Project: Kafka
  Issue Type: Bug
  Components: core
Affects Versions: 2.3.0, 2.1.1, 2.2.0, 2.1.0
Reporter: Alexandre Dupriez


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 consequences, the JMX beans
{code:java}
kafka.cluster:type=Partition,name=UnderReplicated{code}
and 
{code:java}
kafka.cluster:type=Partition,name=UnderMinIsr{code}
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.

 

 
{code:java}
[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{code}
 

 

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.

 



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