[GitHub] [kafka] hachikuji commented on pull request #12499: KAFKA-14154; Ensure AlterPartition not sent to stale controller

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hachikuji commented on PR #12499:
URL: https://github.com/apache/kafka/pull/12499#issuecomment-1211245795

   > So we prevent sending the request if the epoch is lower? And is it the case, that there is always a controller with an epoch at least as large? Or in some cases would we need to wait/retry until such a controller exists?
   
   @jolshan Yes, that is right. Ensuring some level of monotonicity seems like a good general change even outside the original bug. It is weird to allow the broker to send requests to a controller that it knows for sure is stale, and it makes the system harder to reason about. 
   
   One thing I have been trying to think through is how this bug affects kraft. The kraft controller will also return `FENCED_LEADER_EPOCH` if the leader epoch is higher than what it has in its cache. But does kraft give us a stronger guarantee to work with? I think it could, but at the moment, we do not proactively reset the controller in `BrokerToControllerChannelManager` after we discover a new controller. We only reset it after we receive a `NOT_CONTROLLER` error in a request. So it seems to me that we could still hit the same problem with kraft. As a matter of fact, I think this patch does not fix the kraft problem because we do not propagate the controller epoch down to `Partition` so that it can be used in `AlterPartition` requests. cc @jsancio 


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