[jira] [Commented] (FLINK-4233) Simplify leader election / leader session ID assignment

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

    [ https://issues.apache.org/jira/browse/FLINK-4233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16933879#comment-16933879 ] 

TisonKun commented on FLINK-4233:
---------------------------------

Thanks for picking up this topic! I'm thinking of something similar to this one recently.

Basically it requires a new ZKLeaderRetrievalService that works like {{PathChildrenCache}} in Curator(or we just reuse it) to monitoring leader latch registry. In this way, retriever will automatic treat the latch with the smallest sequential number as the leader info node and retrieve the information. As side effects, leader needs not to "publish" its leader information any more.

The downside would be overhead so-called {{PathChildrenCache}} costs. However, given that there is typically 1 or 2 latch at the same time and leader changes(after we tolerate SUSPENDED a.k.a CONNECTIONLOSS) is rare event, hopefully it doesn't impact too much.

> Simplify leader election / leader session ID assignment
> -------------------------------------------------------
>
>                 Key: FLINK-4233
>                 URL: https://issues.apache.org/jira/browse/FLINK-4233
>             Project: Flink
>          Issue Type: Improvement
>          Components: Runtime / Coordination
>    Affects Versions: 1.0.3
>            Reporter: Stephan Ewen
>            Priority: Major
>
> Currently, there are two separate actions and znodes involved in leader election and communication of the leader session ID and leader URL.
> This leads to some quite elaborate code that tries to make sure that the leader session ID and leader URL always eventually converge to those of the leader.
> It is simpler to just encode both the ID and the URL into an id-string that is attached to the leader latch znode. One would have to create a new leader latch each time a contender re-applies for leadership.



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