[jira] [Resolved] (ZOOKEEPER-1912) Leader election lets 2 leaders happen

["Flavio Junqueira (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-1912?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Flavio Junqueira resolved ZOOKEEPER-1912.
-----------------------------------------
    Resolution: Not A Problem

> 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
>            Assignee: Flavio Junqueira
>            Priority: Critical
>         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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