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https://issues.apache.org/jira/browse/YARN-2410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14738773#comment-14738773
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Nathan Roberts commented on YARN-2410:
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Thanks for the additional code comments. +1
> Nodemanager ShuffleHandler can possible exhaust file descriptors
> ----------------------------------------------------------------
>
> Key: YARN-2410
> URL: https://issues.apache.org/jira/browse/YARN-2410
> Project: Hadoop YARN
> Issue Type: Bug
> Components: 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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