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https://issues.apache.org/jira/browse/KAFKA-15021?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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José Armando García Sancio resolved KAFKA-15021.
------------------------------------------------
Resolution: Fixed
> KRaft controller increases leader epoch when shrinking ISR
> ----------------------------------------------------------
>
> Key: KAFKA-15021
> URL: https://issues.apache.org/jira/browse/KAFKA-15021
> Project: Kafka
> Issue Type: Bug
> Components: controller, kraft
> Reporter: José Armando García Sancio
> Assignee: José Armando García Sancio
> Priority: Major
>
> When the KRaft controller shrinks the ISR it also forces the leader epoch to
> increase. This is unnecessary and cases all of the follower replica fetches
> to get invalidated.
> Here is an example trace of this behavior after replica 8 was shutdown:
> {code:java}
> kafka-dump-log --cluster-metadata-decoder --files
> __cluster_metadata-0/00000000000038589501.log | grep Pd7wMb4lSkKI00--SrWNXw
> ...
> | offset: 38655592 CreateTime: 1683849857362 keySize: -1 valueSize: 41
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":7,"topicId":"Pd7wMb4lSkKI00--SrWNXw","isr":[3,1],"leader":1}}
> | offset: 38655593 CreateTime: 1683849857362 keySize: -1 valueSize: 41
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":5,"topicId":"Pd7wMb4lSkKI00--SrWNXw","isr":[0,4],"leader":4}}
> | offset: 38655594 CreateTime: 1683849857362 keySize: -1 valueSize: 41
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":6,"topicId":"Pd7wMb4lSkKI00--SrWNXw","isr":[0,1],"leader":0}}
> | offset: 38656159 CreateTime: 1683849974945 keySize: -1 valueSize: 39
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":7,"topicId":"Pd7wMb4lSkKI00--SrWNXw","isr":[3,1,8]}}
> | offset: 38656256 CreateTime: 1683849994297 keySize: -1 valueSize: 39
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":5,"topicId":"Pd7wMb4lSkKI00--SrWNXw","isr":[0,4,8]}}
> | offset: 38656299 CreateTime: 1683849997139 keySize: -1 valueSize: 39
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":6,"topicId":"Pd7wMb4lSkKI00--SrWNXw","isr":[0,1,8]}}
> | offset: 38657003 CreateTime: 1683850157379 keySize: -1 valueSize: 30
> sequence: -1 headerKeys: [] payload:
> {"type":"PARTITION_CHANGE_RECORD","version":0,"data":{"partitionId":7,"topicId":"Pd7wMb4lSkKI00--SrWNXw","leader":8}}
> {code}
> Also, notice how the leader epoch was not increased when the ISR was expanded.
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