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https://issues.apache.org/jira/browse/ZOOKEEPER-2746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15956067#comment-15956067
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ASF GitHub Bot commented on ZOOKEEPER-2746:
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GitHub user hanm opened a pull request:
https://github.com/apache/zookeeper/pull/213
ZOOKEEPER-2746: remove the check on the new leader after a dynamic re…
…config operation.
This check might not always hold because the nominated leader could fail to
lead the quorum during sync phase - for example if sync time out [when waiting
for quorum
ack](https://github.com/apache/zookeeper/blob/master/src/java/main/org/apache/zookeeper/server/quorum/Leader.java#L1232).
I am thinking we should just remove this instead of fixing it because the
nominated leader is not an interface level contract / guarantee but a best
effort / implementation level details.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hanm/zookeeper ZOOKEEPER-2746
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/zookeeper/pull/213.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #213
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commit 9e367d6f46811233b4bac169f5abb58ff1777273
Author: Michael Han <[email protected]>
Date: 2017-04-04T23:41:09Z
ZOOKEEPER-2746: remove the check on the new leader after a dynamic reconfig
operation.
----
> 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. 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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