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Date: Thu, 10 Sep 2015 15:59:46 +0000 (UTC)
From: "Jason Lowe (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Message-ID: <JIRA.12733524.1407858960000.303163.1441900786663@Atlassian.JIRA>
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Subject: [jira] [Updated] (MAPREDUCE-6474) ShuffleHandler can possibly
 exhaust nodemanager file descriptors
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     [ https://issues.apache.org/jira/browse/MAPREDUCE-6474?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Lowe updated MAPREDUCE-6474:
----------------------------------
    Summary: ShuffleHandler can possibly exhaust nodemanager file descriptors  (was: Nodemanager ShuffleHandler can possible exhaust file descriptors)

> ShuffleHandler can possibly exhaust nodemanager file descriptors
> ----------------------------------------------------------------
>
>                 Key: MAPREDUCE-6474
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6474
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2, nodemanager
>    Affects Versions: 2.5.0
>            Reporter: Nathan Roberts
>            Assignee: Kuhu Shukla
>         Attachments: YARN-2410-v1.patch, YARN-2410-v10.patch, YARN-2410-v11.patch, YARN-2410-v2.patch, YARN-2410-v3.patch, YARN-2410-v4.patch, YARN-2410-v5.patch, YARN-2410-v6.patch, YARN-2410-v7.patch, YARN-2410-v8.patch, YARN-2410-v9.patch
>
>
> The async nature of the shufflehandler can cause it to open a huge number of
> file descriptors, when it runs out it crashes.
> Scenario:
> Job with 6K reduces, slow start set to 0.95, about 40 map outputs per node.
> Let's say all 6K reduces hit a node at about same time asking for their
> outputs. Each reducer will ask for all 40 map outputs over a single socket in a
> single request (not necessarily all 40 at once, but with coalescing it is
> likely to be a large number).
> sendMapOutput() will open the file for random reading and then perform an async transfer of the particular portion of this file(). This will theoretically
> happen 6000*40=240000 times which will run the NM out of file descriptors and cause it to crash.
> The algorithm should be refactored a little to not open the fds until they're
> actually needed. 


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