Status

Current state: "Under Discussion"Accepted

Discussion thread: here

JIRA:

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1. In the current protocol, when the follower sends OffsetForLeaderEpoch request for the partition to the leader, the request includes the latest Leader Epoch in the follower's Leader Epoch Sequence. This step and steps before that are the same as described in KIP-101. 
2. The leader responds with the largest epoch less than or equal to the requested epoch (LeaderEpoch) and the end offset of this epoch (LastOffset).
3. If the follower has LeaderEpoch received from the leader in its Leader Epoch Sequence file, then we go to step 4. Otherwise, 
   1. The follower truncates to the end offset of the largest epoch less than LeaderEpoch, and
   2. The follower sends OffsetForLeaderEpoch request with the largest epoch less than LeaderEpoch, and
   steps
   2.  Steps 2 and 3 repeat until the follower receives the epoch it knows about (the epoch is in the follower's Leader Epoch Sequence file).
4. The By following steps 2 and 3, the follower truncates all offsets with epochs larger than the epoch received from the leader (LeaderEpoch), and then . In this step, the follower truncates its log to the leader's LastOffset, if leader's LastOffset is smaller than follower's Log End Offset.
5. The follower starts fetching from the leader and the remainder of the protocol remains unchanged.

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