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Date: Sun, 21 Feb 2010 20:21:28 +0000 (UTC)
From: "Matei Zaharia (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Commented: (MAPREDUCE-1436) Deadlock in preemption code in
 fair scheduler
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-1436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12836438#action_12836438 ] 

Matei Zaharia commented on MAPREDUCE-1436:
------------------------------------------

You're right Todd, it looks like with the new job retiring process, the JT lock is always grabbed before the fair scheduler lock, and neither of the two deadlocks I pointed out could occur. MAPREDUCE-870 seems to be in both trunk and 0.21, so everything should be fine. However, the issue in MAPREDUCE-1499 does affect Hadoop 0.20 and should be fixed.

> Deadlock in preemption code in fair scheduler
> ---------------------------------------------
>
>                 Key: MAPREDUCE-1436
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1436
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: contrib/fair-share
>    Affects Versions: 0.21.0, 0.22.0
>            Reporter: Matei Zaharia
>            Assignee: Matei Zaharia
>            Priority: Blocker
>         Attachments: deadlock.png, mapreduce-1436-v2.patch, mapreduce-1436.patch
>
>
> In testing the fair scheduler with preemption, I found a deadlock between updatePreemptionVariables and some code in the JobTracker. This was found while testing a backport of the fair scheduler to Hadoop 0.20, but it looks like it could also happen in trunk and 0.21. Details are in a comment below.

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