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https://issues.apache.org/jira/browse/ZOOKEEPER-3471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16953222#comment-16953222
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Michael Han commented on ZOOKEEPER-3471:
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Thanks [~lvfangmin] for getting back on this. Your reply explained well on the
race condition. My initial understanding after reading problem description was
that this was a quorum level problem (where my confusions came from) but it
actually is a local (learner specific) problem, which now makes sense to me.
> Potential lock unavailable due to dangling ephemeral nodes left during local
> session upgrading
> ----------------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3471
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3471
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.6.0
> Reporter: Fangmin Lv
> Assignee: Fangmin Lv
> Priority: Critical
> Labels: pull-request-available
> Fix For: 3.6.0
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> There is a race condition which might be triggered if the client create
> session, upgrading the session with ephemeral node, then immediately issued
> close session request before it's removed from local session tracker.
>
> The close session request will be treated as a local session close request
> since it still exists in the local session tracker, which goes through the ZK
> pipeline and delete the session from both local and global session tracker.
> Since the session is not tracked anymore, it will leave the ephemeral nodes
> there.
>
>
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