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https://issues.apache.org/jira/browse/KAFKA-15353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17759179#comment-17759179
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Calvin Liu commented on KAFKA-15353:
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[~mimaison]
If I understand correctly, in ZK mode, the leader can send AlterPartition
request to empty the ISR. But the leader will continue to serve as the leader.
If the leader stays alive, the previous ISR members except itself will be added
back. I guess the partition will stay in this wield "leader not in ISR" state
until the leadership is changed.
If the leader fails before any followers can be added to the ISR, an unclean
leader election will be required.
> Empty ISR returned from controller after AlterPartition request
> ---------------------------------------------------------------
>
> Key: KAFKA-15353
> URL: https://issues.apache.org/jira/browse/KAFKA-15353
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 3.5.0
> Reporter: Luke Chen
> Assignee: Calvin Liu
> Priority: Blocker
> Fix For: 3.6.0, 3.5.2
>
>
> In
> [KIP-903|https://cwiki.apache.org/confluence/display/KAFKA/KIP-903%3A+Replicas+with+stale+broker+epoch+should+not+be+allowed+to+join+the+ISR],
> (more specifically this [PR|https://github.com/apache/kafka/pull/13408]), we
> bumped the AlterPartitionRequest version to 3 to use `NewIsrWithEpochs` field
> instead of `NewIsr` one. And when building the request for older version,
> we'll manually convert/downgrade the request into the older version for
> backward compatibility
> [here|https://github.com/apache/kafka/blob/6bd17419b76f8cf8d7e4a11c071494dfaa72cd50/clients/src/main/java/org/apache/kafka/common/requests/AlterPartitionRequest.java#L85-L96],
> to extract ISR info from `NewIsrWithEpochs` and then fill in the `NewIsr`
> field, and then clear the `NewIsrWithEpochs` field.
>
> The problem is, when the AlterPartitionRequest sent out for the first time,
> if there's some transient error (ex: NOT_CONTROLLER), we'll retry. On the
> retry, we'll build the AlterPartitionRequest again. But this time, the
> request data is the one that already converted above. At this point, when we
> try to extract the ISR from `NewIsrWithEpochs`, we'll get empty. So, we'll
> send out an AlterPartition request with empty ISR, and impacting the kafka
> availability.
>
> From the log, I can see this:
> {code:java}
> [2023-08-16 03:57:55,122] INFO [Partition test_topic-1 broker=3] ISR updated
> to (under-min-isr) and version updated to 9 (kafka.cluster.Partition)
> ...
> [2023-08-16 03:57:55,157] ERROR [ReplicaManager broker=3] Error processing
> append operation on partition test_topic-1
> (kafka.server.ReplicaManager)org.apache.kafka.common.errors.NotEnoughReplicasException:
> The size of the current ISR Set() is insufficient to satisfy the min.isr
> requirement of 2 for partition test_topic-1 {code}
>
> h4. *Impact:*
> This will happen when users trying to upgrade from versions < 3.5.0 to 3.5.0
> or later. During the rolling upgrade, there will be some nodes in v3.5.0, and
> some are not. So, for the node in v3.5.0 will try to build an old version of
> AlterPartitionRequest. And then, if it happen to have some transient error
> during the AlterPartitionRequest send, the ISR will be empty and no producers
> will be able to write data to the partitions.
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