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https://issues.apache.org/jira/browse/KAFKA-7040?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16590634#comment-16590634
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Lucas Wang commented on KAFKA-7040:
-----------------------------------

[~lindong] Sure, I will own this ticket and work on the fix.

> The replica fetcher thread may truncate accepted messages during multiple 
> fast leadership transitions
> -----------------------------------------------------------------------------------------------------
>
>                 Key: KAFKA-7040
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7040
>             Project: Kafka
>          Issue Type: Bug
>          Components: replication
>            Reporter: Lucas Wang
>            Priority: Minor
>
> Problem Statement:
> Consider the scenario where there are two brokers, broker0, and broker1, and 
> there are two partitions "t1p0", and "t1p1"[1], both of which have broker1 as 
> the leader and broker0 as the follower. The following sequence of events 
> happened on broker0
> 1. The replica fetcher thread on a broker0 issues a LeaderEpoch request to 
> broker1, and awaits to get the response
> 2. A LeaderAndISR request causes broker0 to become the leader for one 
> partition t1p0, which in turn will remove the partition t1p0 from the replica 
> fetcher thread
> 3. Broker0 accepts some messages from a producer
> 4. A 2nd LeaderAndISR request causes broker1 to become the leader, and 
> broker0 to become the follower for partition t1p0. This will cause the 
> partition t1p0 to be added back to the replica fetcher thread on broker0.
> 5. The replica fetcher thread on broker0 receives a response for the 
> LeaderEpoch request issued in step 1, and truncates the accepted messages in 
> step3.
> The issue can be reproduced with the test from 
> https://github.com/gitlw/kafka/commit/8956e743f0e432cc05648da08c81fc1167b31bea
> [1] Initially we set up broker0 to be the follower of two partitions instead 
> of just one, to avoid the shutting down of the replica fetcher thread when it 
> becomes idle.



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