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https://issues.apache.org/jira/browse/ZOOKEEPER-3471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16905643#comment-16905643
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Michael Han commented on ZOOKEEPER-3471:
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[~lvfangmin] I feel I get the race condition you described at a high level, but
I had a hard time to actually construct a conceptual model on the race that
maps to the code (due to the convoluted session handling codes).
Do you mind to provide a little bit more concrete examples on where exactly the
race happening? In particular:
bq. delete the session from both local and global session tracker
Does this happen before or after the session upgrade finish? As we know, the
session upgrade finishing by commit a session in quorum, so if this delete from
session tracker finishes before session upgrading finish, then the commit
session will re-add the session back; if this delete is finished after session
upgrading finish, then we still have the session on other quorum servers. So
every case seems ok?
> 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: 0.5h
> 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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