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https://issues.apache.org/jira/browse/KAFKA-13173?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17394319#comment-17394319
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Jason Gustafson commented on KAFKA-13173:
-----------------------------------------
I upgraded this bug to a blocker because I think it can result in data loss.
For example, in the example above, the second ISR change would be interpreted
as an expansion, but there may have been committed writes to the log between
the two ISR changes which were not reflected in the expansion.
> KRaft controller does not handle simultaneous broker expirations correctly
> --------------------------------------------------------------------------
>
> Key: KAFKA-13173
> URL: https://issues.apache.org/jira/browse/KAFKA-13173
> Project: Kafka
> Issue Type: Bug
> Reporter: Jason Gustafson
> Assignee: Niket Goel
> Priority: Blocker
> Fix For: 3.0.0
>
>
> In `ReplicationControlManager.fenceStaleBrokers`, we find all of the current
> stale replicas and attempt to remove them from the ISR. However, when
> multiple expirations occur at once, we do not properly accumulate the ISR
> changes. For example, I ran a test where the ISR of a partition was
> initialized to [1, 2, 3]. Then I triggered a timeout of replicas 2 and 3 at
> the same time. The records that were generated by `fenceStaleBrokers` were
> the following:
> {code}
> ApiMessageAndVersion(PartitionChangeRecord(partitionId=0,
> topicId=_seg8hBuSymBHUQ1sMKr2g, isr=[1, 3], leader=1, replicas=null,
> removingReplicas=null, addingReplicas=null) at version 0),
> ApiMessageAndVersion(FenceBrokerRecord(id=2, epoch=102) at version 0),
> ApiMessageAndVersion(PartitionChangeRecord(partitionId=0,
> topicId=_seg8hBuSymBHUQ1sMKr2g, isr=[1, 2], leader=1, replicas=null,
> removingReplicas=null, addingReplicas=null) at version 0),
> ApiMessageAndVersion(FenceBrokerRecord(id=3, epoch=103) at version 0)]
> {code}
> First the ISR is shrunk to [1, 3] as broker 2 is fenced. We also see the
> record to fence broker 2. Then the ISR is modified to [1, 2] as the fencing
> of broker 3 is handled. So we did not account for the fact that we had
> already fenced broker 2 in the request.
> A simple solution for now is to change the logic to handle fencing only one
> broker at a time.
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