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Date: Wed, 8 Dec 2010 06:48:00 -0500 (EST)
From: "Kristian Waagan (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Resolved: (DERBY-4928) Deadlock-prone synchronization in
 BasicDependencyManager
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     [ https://issues.apache.org/jira/browse/DERBY-4928?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kristian Waagan resolved DERBY-4928.
------------------------------------

          Resolution: Fixed
       Fix Version/s: 10.8.0.0
    Issue & fix info:   (was: [Patch Available])

Thanks for the review, Knut.
I fixed the comment before committing patch 1a to trunk with revision 1043367.

I don't plan to backport this fix, at least not now. We don't have any reports for this problem for earlier versions, so I'd rather see that the changes go through more testing before backporting.
For the record, it was the automatic index statistics update feature that triggered the bug.

> Deadlock-prone synchronization in BasicDependencyManager
> --------------------------------------------------------
>
>                 Key: DERBY-4928
>                 URL: https://issues.apache.org/jira/browse/DERBY-4928
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.8.0.0
>            Reporter: Kristian Waagan
>            Assignee: Kristian Waagan
>             Fix For: 10.8.0.0
>
>         Attachments: derby-4928-1a-depman_sync_and_cleanup.diff
>
>
> The synchronization in BasicDependencyManager is prone to deadlock, because database locks are obtained while holding the monitor on "this".
> Problem observed when testing the automatic index statistics update prototype.
> There are comments in the file suggesting that in-memory dependencies should be accessed while holding the Java monitor, but the monitor should not be held when accessing stored dependencies. The implementation is breaking this rule/suggestion.

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