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https://issues.apache.org/jira/browse/ZOOKEEPER-1912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13969360#comment-13969360
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Flavio Junqueira commented on ZOOKEEPER-1912:
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Thanks for reporting this. Having two servers thinking they could be leaders is
not really a bug. It is a bug if we have two servers leading and both having
quorums of supporters concurrently, which your case doesn't seem to imply.
If you can find a way of reducing the amount of time we have concurrent
leaders, then fine with me, but in my experience it doesn't happen often.
Your tool sounds like a cool one!
> Leader election lets 2 leaders happen
> -------------------------------------
>
> Key: ZOOKEEPER-1912
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1912
> Project: ZooKeeper
> Issue Type: Bug
> Components: leaderElection
> Affects Versions: 3.4.6
> Environment: Ubuntu 12.04, OpenJDK 1.6
> Reporter: Tanakorn Leesatapornwongsa
> Priority: Minor
> Attachments: conf.zip, log.zip
>
>
> In 3-node cluster, when there are 2 nodes die and reboot during leader
> election, it might lead to the case that there are 2 leaders happen in the
> system. Eventually, a leader that does not has follower supports and quit
> being leader, but it makes us lose some availability.
> I am building a tools that can reorder messages and disk write, and also
> inject node crash to the system and found this bug.
> These are the step of events that my tools execute in sequence that lead to 2
> leaders at the end.
> My zookeeper nodes have id = 0,1,2
> packetsend from=0 to=1 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=0 to=2 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=2 to=0 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=2 to=1 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=1 to=0 state=0 leader=1 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=1 to=2 state=0 leader=1 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=1 to=0 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=0 to=1 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=1 to=2 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=0 to=2 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> diskwrite nodeId=0 write=currentEpoch
> nodecrash id=0
> nodecrash id=1
> nodestart id=0
> nodestart id=1
> diskwrite nodeId=2 write=currentEpoch
> packetsend from=2 to=0 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=0 to=2 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=1 state=0 leader=2 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=0 to=1 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=0 state=0 leader=1 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=1 to=2 state=0 leader=1 zxid=0 electionEpoch=1 peerEpoch=0
> packetsend from=2 to=0 state=2 leader=2 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=0 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=1 state=2 leader=2 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=2 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=1 state=2 leader=2 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=0 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=2 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=0 to=1 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=1 state=2 leader=2 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=0 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=2 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=0 to=1 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=1 state=2 leader=2 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=0 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=1 to=2 state=0 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=0 to=1 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=0 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=2 to=1 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=0 to=2 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=0 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=1 to=0 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=1 to=2 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=2 to=1 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=0 to=2 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=0 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=0 to=1 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> packetsend from=2 to=1 state=0 leader=2 zxid=0 electionEpoch=2 peerEpoch=1
> packetsend from=0 to=2 state=2 leader=0 zxid=0 electionEpoch=1 peerEpoch=1
> diskwrite nodeId=2 write=currentEpoch
> diskwrite nodeId=1 write=currentEpoch
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