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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2746) Leader hand off during dynamic reconfig is a best effort, not a guarantee, when none trivial changes happen on current leader.
Date Tue, 04 Apr 2017 23:53:41 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15956074#comment-15956074
] 

ASF GitHub Bot commented on ZOOKEEPER-2746:
-------------------------------------------

Github user shralex commented on the issue:

    https://github.com/apache/zookeeper/pull/213
  
    LGTM


> Leader hand off during dynamic reconfig is a best effort, not a guarantee, when none
trivial changes happen on current leader.
> ------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2746
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2746
>             Project: ZooKeeper
>          Issue Type: Test
>    Affects Versions: 3.5.2
>            Reporter: Michael Han
>            Assignee: Michael Han
>
> When none trivial config change happens on the leader (e.g. port change, role change)
to minimize disruption of quorum we do leader hand off by having the current leader nominate
the next leader instead of kicking off a full leader election.
> However this is a best effort and not a guarantee that the new leader of the quorum will
be the nominated leader: it is possible that the nominated leader fail to establish the leadership
during sync phase, which leads to new election rounds and a different leader elected. 
> In ReconfigTest.testPortChange one check is the new leader after dynamic reconfig of
the current leader has to be a different leader; based on what described earlier this is not
always the case as the nominated leader might fail to get a quorum to ack its leadership during
sync phase, and the old leader might end up as the new leader. We could either fixed the test
by removing the check, or always guarantee that the new leader after dynamic reconfig is the
nominated leader (which does not make much sense given the nominated leader also has a possibility
to crash.).



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