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https://issues.apache.org/jira/browse/ZOOKEEPER-2307?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Arshad Mohammad updated ZOOKEEPER-2307:
---------------------------------------
    Attachment: ZOOKEEPER-2307-01.patch

Submitting test patch ZOOKEEPER-2307-01.patch to reproduce the scenario, also 
to have better understanding of the scenario. Please review the proposed 
solution.

> ZooKeeper not starting because acceptedEpoch is less than the currentEpoch
> --------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2307
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2307
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>            Reporter: Arshad Mohammad
>            Assignee: Arshad Mohammad
>            Priority: Critical
>             Fix For: 3.5.2, 3.6.0
>
>         Attachments: ZOOKEEPER-2307-01.patch
>
>
> This issue occurred in one of our test environment where disk was being 
> changed to read only very frequently.
> The the scenario is as follows:
> # Configure three node ZooKeeper cluster, lets say nodes are A, B and C
> # Start A and B. Both A and B start successfully, quorum is running.
> # Start C, because of IO error C fails to update acceptedEpoch file. But C 
> also starts successfully, joins the quorum as follower
> # Stop C
> # Start C, bellow exception with message "The accepted epoch, 0 is less than 
> the current epoch, 1" is thrown
> {code}
> 2015-10-29 16:52:32,942 [myid:3] - ERROR [main:QuorumPeer@784] - Unable to 
> load database on disk
> java.io.IOException: The accepted epoch, 0 is less than the current epoch, 1
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeer.loadDataBase(QuorumPeer.java:781)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeer.start(QuorumPeer.java:720)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeerMain.runFromConfig(QuorumPeerMain.java:202)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeerMain.initializeAndRun(QuorumPeerMain.java:139)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeerMain.main(QuorumPeerMain.java:88)
> 2015-10-29 16:52:32,946 [myid:3] - ERROR [main:QuorumPeerMain@111] - 
> Unexpected exception, exiting abnormally
> java.lang.RuntimeException: Unable to run quorum server 
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeer.loadDataBase(QuorumPeer.java:785)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeer.start(QuorumPeer.java:720)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeerMain.runFromConfig(QuorumPeerMain.java:202)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeerMain.initializeAndRun(QuorumPeerMain.java:139)
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeerMain.main(QuorumPeerMain.java:88)
> Caused by: java.io.IOException: The accepted epoch, 0 is less than the 
> current epoch, 1
>       at 
> org.apache.zookeeper.server.quorum.QuorumPeer.loadDataBase(QuorumPeer.java:781)
> {code}



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