[jira] [Commented] (RATIS-2311) Allow TransferLeadership#isFollowerUpToDate to wait for appliedIndex

["Elia Renzoni (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/RATIS-2311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18110642#comment-18110642 ] 

Elia Renzoni commented on RATIS-2311:
-------------------------------------

[~szetszwo] [~ivanandika] I'd like to work on this issue if it's still open and relevant. Could you assign it to me? Thanks!

> Allow TransferLeadership#isFollowerUpToDate to wait for appliedIndex
> --------------------------------------------------------------------
>
>                 Key: RATIS-2311
>                 URL: https://issues.apache.org/jira/browse/RATIS-2311
>             Project: Ratis
>          Issue Type: Improvement
>          Components: Leader
>            Reporter: Ivan Andika
>            Assignee: Tsz-wo Sze
>            Priority: Major
>
> Currently TransferLeadership#isFollowerUpToDate only waits for the up-to-date matchIndex before triggering election on the target Ratis server.
> However, if the target Ratis server appliedIndex is way below the matchIndex, once the Ratis server is promoted to a leader, it might take a while for it to catch up to the current appliedIndex and acknowlegding the requests. This can have a noticeable effect on the latency and throughput of the Raft group.
> We might make the transfer leadership check to be more strict by ensuring that leader and follower appliedIndex gap is within a certain acceptable threshold (e.g 10,000) so that the leader catch up would be less noticeable.



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