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https://issues.apache.org/jira/browse/ZOOKEEPER-582?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benjamin Reed updated ZOOKEEPER-582:
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Hadoop Flags: [Reviewed]
+1 great job mahadev!
> ZooKeeper can revert to old data when a snapshot is created outside of normal
> processing
> ----------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-582
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-582
> Project: Zookeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.1.1, 3.2.1
> Reporter: Benjamin Reed
> Assignee: Mahadev konar
> Priority: Blocker
> Fix For: 3.1.2, 3.2.2, 3.3.0
>
> Attachments: test.patch, ZOOKEEPER-582.patch, ZOOKEEPER-582.patch,
> ZOOKEEPER-582.patch, ZOOKEEPER-582.patch, ZOOKEEPER-582.patch,
> ZOOKEEPER-582_3.1.patch, ZOOKEEPER-582_3.2.patch, ZOOKEEPER-582_3.2.patch
>
>
> when zookeeper starts up it will restore the most recent state (latest zxid)
> it finds in the data directory. unfortunately, in the quorum version of
> zookeeper updates are logged using an epoch based on the latest log file in a
> directory. if there is a snapshot with a higher epoch than the log files, the
> zookeeper server will start logging using an epoch one higher than the
> highest log file.
> so if a data directory has a snapshot with an epoch of 27 and there are no
> log files, zookeeper will start logging changes using epoch 1. if the cluster
> restarts the state will be restored from the snapshot with the epoch of 27,
> which in effect, restores old data.
> normal operation of zookeeper will never result in this situation.
> this does not effect standalone zookeeper.
> a fix should make sure to use an epoch one higher than the current state,
> whether it comes from the snapshot or log, and should include a sanity check
> to make sure that a follower never connects to a leader that has a lower
> epoch than its own.
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