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https://issues.apache.org/jira/browse/KAFKA-14608?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Grant updated KAFKA-14608:
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Summary: Look into when reassignment should be completed in KRaft mode
(was: Make sure reassignment does not cause under min ISR)
> Look into when reassignment should be completed in KRaft mode
> -------------------------------------------------------------
>
> Key: KAFKA-14608
> URL: https://issues.apache.org/jira/browse/KAFKA-14608
> Project: Kafka
> Issue Type: Improvement
> Reporter: Andrew Grant
> Assignee: Andrew Grant
> Priority: Major
>
> In KRaft mode we complete reassignments when the adding replicas have been
> added to the ISR - see
> [https://github.com/apache/kafka/blob/trunk/metadata/src/main/java/org/apache/kafka/controller/PartitionChangeBuilder.java#L288.]
> As a result its possible for the partition to be under min ISR if the number
> of adding replicas is less than the topic's under min ISR config and some
> other target replicas are not in the ISR for whatever reason.
> This behavior differs to ZK mode where we require all target replicas to be
> in the ISR for the reassignment to complete - see
> [https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/controller/KafkaController.scala#L1003].
>
> I thought more about it and I only think the reassignment can be completed
> *and* we are under min ISR if either 1) we were already under min ISR in the
> first place or 2) the replication factor decreases. So in practice I dont
> think this is a severe issue.
> It seems there are two options. One is to match the ZK behavior and only
> complete reassignments when all target replicas are in the ISR. The second is
> to complete reassignments when enough target replicas are in the ISR such
> that we're above under min ISR. So if the under min ISR config for a topic is
> two, then we would complete reassignments when at least two target replicas
> are in the ISR.
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