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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2746) Leader hand-off during dynamic reconfig is best effort, while test always expects it
Date Wed, 05 Apr 2017 00:04:41 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15956083#comment-15956083

Hadoop QA commented on ZOOKEEPER-2746:

-1 overall.  GitHub Pull Request  Build

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 3 new or modified tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 3.0.1) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit

    -1 core tests.  The patch failed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/503//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/503//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/503//console

This message is automatically generated.

> Leader hand-off during dynamic reconfig is best effort, while test always expects it
> ------------------------------------------------------------------------------------
>                 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
>             Fix For: 3.6.0
> When non-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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