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https://issues.apache.org/jira/browse/ZOOKEEPER-569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12829326#action_12829326
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Hadoop QA commented on ZOOKEEPER-569:
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+1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12434729/zookeeper-569.patch
against trunk revision 903483.
+1 @author. The patch does not contain any @author tags.
+1 tests included. The patch appears to include 5 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 warnings.
+1 release audit. The applied patch does not increase the total number of
release audit warnings.
+1 core tests. The patch passed core unit tests.
+1 contrib tests. The patch passed contrib unit tests.
Test results:
http://hudson.zones.apache.org/hudson/job/Zookeeper-Patch-h7.grid.sp2.yahoo.net/65/testReport/
Findbugs warnings:
http://hudson.zones.apache.org/hudson/job/Zookeeper-Patch-h7.grid.sp2.yahoo.net/65/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output:
http://hudson.zones.apache.org/hudson/job/Zookeeper-Patch-h7.grid.sp2.yahoo.net/65/console
This message is automatically generated.
> Failure of elected leader can lead to never-ending leader election
> ------------------------------------------------------------------
>
> Key: ZOOKEEPER-569
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-569
> Project: Zookeeper
> Issue Type: Bug
> Reporter: Henry Robinson
> Assignee: Henry Robinson
> Fix For: 3.3.0
>
> Attachments: zookeeper-569.patch, zookeeper-569.patch,
> zookeeper-569.patch
>
>
> It is possible for basic LeaderElection to enter a situation where it never
> terminates.
> As an example, consider a three node cluster A, B and C.
> 1. In the first round, A votes for A, B votes for B and C votes for C
> 2. Since C > B > A, all nodes resolve to vote for C in the second round as
> there is no first round winner
> 3. A, B vote for C, but C fails.
> 4. C is not elected because neither A nor B hear from it, and so votes for it
> are discarded
> 5. A and B never reset their votes, despite not hearing from C, so continue
> to vote for it ad infinitum.
> Step 5 is the bug. If A and B reset their votes to themselves in the case
> where the heard-from vote set is empty, leader election will continue.
> I do not know if this affects running ZK clusters, as it is possible that the
> out-of-band failure detection protocols may cause leader election to be
> restarted anyhow, but I've certainly seen this in tests.
> I have a trivial patch which fixes it, but it needs a test (and tests for
> race conditions are hard to write!)
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