[jira] [Resolved] (KAFKA-13837) Return error for Fetch requests from unrecognized followers

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

     [ https://issues.apache.org/jira/browse/KAFKA-13837?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Gustafson resolved KAFKA-13837.
-------------------------------------
    Fix Version/s: 3.3.0
       Resolution: Fixed

> Return error for Fetch requests from unrecognized followers
> -----------------------------------------------------------
>
>                 Key: KAFKA-13837
>                 URL: https://issues.apache.org/jira/browse/KAFKA-13837
>             Project: Kafka
>          Issue Type: Bug
>            Reporter: Jason Gustafson
>            Assignee: Jason Gustafson
>            Priority: Major
>             Fix For: 3.3.0
>
>
> If the leader of a partition receives a request from a replica which is not in the current replica set, we currently return an empty fetch response with no error. I think the rationale for this is that the leader may not have received the latest `LeaderAndIsr` update which adds the replica, so we just want the follower to retry. The problem with this is that if the `LeaderAndIsr` request never arrives, then there might not be an external indication of a problem. This probably was the only reasonable option before we added the leader epoch to the `Fetch` request API. Now that we have it, it would be clearer to return an `UNKNOWN_LEADER_EPOCH` error to indicate that the (replicaId, leaderEpoch) tuple is not recognized. 



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