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From "Jukka Zitting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-2000) Deadlock on concurrent commits
Date Tue, 03 Mar 2009 12:40:56 GMT

    [ https://issues.apache.org/jira/browse/JCR-2000?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12678306#action_12678306
] 

Jukka Zitting commented on JCR-2000:
------------------------------------

As far as I can tell, the lockups are caused by the test case forcibly terminating long-lived
threads. The Thread.stop() call does unlock any object monitors the thread has locked, but
will leave the explicit lock objects locked.

The proposed change extends the scope of the versioning lock used in transactions, and thus
affects the performance of concurrent commits. This is probably the cause of the timeouts
of the test case being reached.

> Deadlock on concurrent commits
> ------------------------------
>
>                 Key: JCR-2000
>                 URL: https://issues.apache.org/jira/browse/JCR-2000
>             Project: Jackrabbit Content Repository
>          Issue Type: Bug
>          Components: jackrabbit-core, transactions
>    Affects Versions: 1.5.3
>            Reporter: Jukka Zitting
>            Assignee: Jukka Zitting
>             Fix For: 1.5.4
>
>         Attachments: JCR-2000.patch, JCR-2000.patch
>
>
> As reported in the followup to JCR-1979, there's a case where two transactions may be
concurrently inside a commit. This is bad as it breaks the main assumption in http://jackrabbit.apache.org/concurrency-control.html
about all transactions first acquiring the versioning write lock.
> Looking deeper into this I find that the versioning write lock is only acquired if the
transaction being committed contains versioning operations. This is incorrect as all transactions
in any case need to access the version store when checking for references.

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