Hadoop QA commented on ZOOKEEPER-569:

+1 overall.  Here are the results of testing the latest attachment 
  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: 
Findbugs warnings: 
Console output: 

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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