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https://issues.apache.org/jira/browse/ZOOKEEPER-3144?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Han resolved ZOOKEEPER-3144.
------------------------------------
Resolution: Fixed
Issue resolved by pull request 621
[https://github.com/apache/zookeeper/pull/621]
> Potential ephemeral nodes inconsistent due to global session inconsistent
> with fuzzy snapshot
> ---------------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3144
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3144
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.5.4, 3.6.0, 3.4.13
> Reporter: Fangmin Lv
> Assignee: Fangmin Lv
> Priority: Critical
> Labels: pull-request-available
> Fix For: 3.6.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Found this issue recently when checking another prod issue, the problem is
> that the current code will update lastProcessedZxid before it's actually
> making change for the global sessions in the DataTree.
>
> In case there is a snapshot taking in progress, and there is a small time
> stall between set lastProcessedZxid and update the session in DataTree due to
> reasons like thread context switch or GC, etc, then it's possible the
> lastProcessedZxid is actually set to the future which doesn't include the
> global session change (add or remove).
>
> When reload this snapshot and it's txns, it will replay txns from
> lastProcessedZxid + 1, so it won't create the global session anymore, which
> could cause data inconsistent.
>
> When global sessions are inconsistent, it might have ephemeral inconsistent
> as well, since the leader will delete all the ephemerals locally if there is
> no global sessions associated with it, and if someone have snapshot sync with
> it then that server will not have that ephemeral as well, but others will. It
> will also have global session renew issue for that problematic session.
>
> The same issue exist for the closeSession txn, we need to move these global
> session update logic before processTxn, so the lastProcessedZxid will not
> miss the global session here.
>
>
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