[jira] [Resolved] (KAFKA-10706) Liveness bug in truncation protocol can lead to indefinite URP

["Jason Gustafson (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-10706?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Gustafson resolved KAFKA-10706.
-------------------------------------
    Fix Version/s: 2.7.1
                   2.6.1
                   2.5.2
                   2.4.2
       Resolution: Fixed

> Liveness bug in truncation protocol can lead to indefinite URP
> --------------------------------------------------------------
>
>                 Key: KAFKA-10706
>                 URL: https://issues.apache.org/jira/browse/KAFKA-10706
>             Project: Kafka
>          Issue Type: Bug
>            Reporter: Jason Gustafson
>            Assignee: Jason Gustafson
>            Priority: Major
>             Fix For: 2.4.2, 2.5.2, 2.6.1, 2.7.1
>
>
> We hit an interesting liveness condition in the truncation protocol. Broker A was leader in epoch 7, broker B was leader in epoch 8, and then broker A was leader in epoch 9 again.
> On broker A, we had the following state in the epoch cache:
> {code}
> epoch 4, start offset 3953
> epoch 7, start offset 3983
> epoch 9, start offset 3988
> {code}
> On broker B, we had the following:
> {code}
> epoch 4, start offset 3953
> epoch 8, start offset 3983
> {code}
> After A was elected, broker B sent epoch 8 in OffsetsForLeaderEpoch. Broker A correctly responded with epoch 7 ending at offset 3988. The end offset on broker B was in fact 3983, so this truncation had no effect. Broker B then retried with epoch 8 again and replication was stuck. 
> When a replica becomes leader, it first inserts an entry into the epoch cache with the current log end offset. This ensures that that it has a larger epoch in the cache than any epoch that could be requested by a valid replica. However, I think it is incorrect to turn around and use this epoch when becoming a follower. It seems like we need symmetric logic after becoming a follower to remove this epoch entry.



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