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https://issues.apache.org/jira/browse/ZOOKEEPER-1653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15094048#comment-15094048
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Arshad Mohammad commented on ZOOKEEPER-1653:
--------------------------------------------
Created new jira ZOOKEEPER-2354 for merging this important fix to master and
3.5 branch.
> zookeeper fails to start because of inconsistent epoch
> ------------------------------------------------------
>
> Key: ZOOKEEPER-1653
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1653
> Project: ZooKeeper
> Issue Type: Bug
> Components: quorum
> Affects Versions: 3.4.5
> Reporter: Michi Mutsuzaki
> Assignee: Michi Mutsuzaki
> Priority: Blocker
> Fix For: 3.4.6
>
> Attachments: ZOOKEEPER-1653.3.4.patch, ZOOKEEPER-1653.3.4.patch,
> ZOOKEEPER-1653.3.4.patch, ZOOKEEPER-1653.patch, ZOOKEEPER-1653.patch
>
>
> It looks like QuorumPeer.loadDataBase() could fail if the server was
> restarted after zk.takeSnapshot() but before finishing
> self.setCurrentEpoch(newEpoch) in Learner.java.
> {code:java}
> case Leader.NEWLEADER: // it will be NEWLEADER in v1.0
> zk.takeSnapshot();
> self.setCurrentEpoch(newEpoch); // <<< got restarted here
> snapshotTaken = true;
> writePacket(new QuorumPacket(Leader.ACK, newLeaderZxid, null, null),
> true);
> break;
> {code}
> The server fails to start because currentEpoch is still 1 but the last
> processed zkid from the snapshot has been updated.
> {noformat}
> 2013-02-20 13:45:02,733 5543 [pool-1-thread-1] ERROR
> org.apache.zookeeper.server.quorum.QuorumPeer - Unable to load database on
> disk
> java.io.IOException: The current epoch, 1, is older than the last zxid,
> 8589934592
> at
> org.apache.zookeeper.server.quorum.QuorumPeer.loadDataBase(QuorumPeer.java:439)
> at
> org.apache.zookeeper.server.quorum.QuorumPeer.start(QuorumPeer.java:413)
> ...
> {noformat}
> {noformat}
> $ find datadir
> datadir
> datadir/version-2
> datadir/version-2/currentEpoch.tmp
> datadir/version-2/acceptedEpoch
> datadir/version-2/snapshot.0
> datadir/version-2/currentEpoch
> datadir/version-2/snapshot.200000000
> $ cat datadir/version-2/currentEpoch.tmp
> 2%
> $ cat datadir/version-2/acceptedEpoch
> 2%
> $ cat datadir/version-2/currentEpoch
> 1%
> {noformat}
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