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From "Thomas Graves (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4842) Shuffle race can hang reducer
Date Tue, 18 Dec 2012 02:24:15 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4842?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13534547#comment-13534547
] 

Thomas Graves commented on MAPREDUCE-4842:
------------------------------------------

I ran some shuffle and sort tests and on the shuffle test job times were ~90 seconds worse
with Asokan's patch then without, with that time being take by reducers. Sort test was showing
a wide variation.  One run took 680 seconds, the next 770 seconds. I don't normally see that
much difference between runs. The runs without the patch were 680 and 700 seconds.
                
> 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: 2.0.2-alpha, 0.23.5
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>            Priority: Blocker
>         Attachments: mapreduce-4842.patch, MAPREDUCE-4842.patch, MAPREDUCE-4842.patch,
MAPREDUCE-4842.patch, 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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