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Posted to mapreduce-issues@hadoop.apache.org by "Arun C Murthy (JIRA)" <ji...@apache.org> on 2012/12/04 14:50:58 UTC

[jira] [Updated] (MAPREDUCE-4842) Shuffle race can hang reducer

     [ https://issues.apache.org/jira/browse/MAPREDUCE-4842?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Arun C Murthy updated MAPREDUCE-4842:
-------------------------------------

    Attachment: MAPREDUCE-4842.patch

Great catch Jason! Thanks!

It seems like we are missing a hook in MergeThread.run to re-check the condition and trigger another merge at the end of the merge itself.

Here is an illustrative patch.

Thoughts?
                
> Shuffle race can hang reducer
> -----------------------------
>
>                 Key: MAPREDUCE-4842
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4842
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 2.0.3-alpha, 0.23.5
>            Reporter: Jason Lowe
>         Attachments: MAPREDUCE-4842.patch
>
>
> Saw an instance where the shuffle caused multiple reducers in a job to hang.  It looked similar to the problem described in MAPREDUCE-3721, where the fetchers were all being told to WAIT by the MergeManager but no merge was taking place.

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