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