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https://issues.apache.org/jira/browse/ZOOKEEPER-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17893167#comment-17893167
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Kezhu Wang commented on ZOOKEEPER-4882:
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The leader branch might be a little complicated as it take a clean snapshot
before leading. But once it is restarted, it has no much difference to the
follower case.
> Data loss after restarting an node experienced temporary disk error and rejoin
> ------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-4882
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4882
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.8.4, 3.9.3
> Reporter: Kezhu Wang
> Priority: Major
>
> The cause is multifold:
> 1. Leader will commit a proposal once quorum acked.
> 2. Proposal is able to be committed in node's memory even if it has not
> been written to that node's disk.
> 3. In case of disk error, the txn log could lag behind memory database.
> The above applies to both leader and follower. I have not verified leader
> branch, let's consider only follower for now.
> f4. A follower experienced temporary disk error will have hole in txn log
> after re-join.
> f5. Restarted follower will lose the data. Worse, it is able to win
> election and propagate data loss to whole cluster.
> I authored commits in my repo to expose this.
> https://github.com/kezhuw/zookeeper/commits/data-loss-temporary-sync-disk-error/
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