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https://issues.apache.org/jira/browse/YARN-2410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14626717#comment-14626717
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Hadoop QA commented on YARN-2410:
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:red}-1{color} | patch |   0m  0s | The patch command could not apply 
the patch during dryrun. |
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|| Subsystem || Report/Notes ||
| Patch URL | 
http://issues.apache.org/jira/secure/attachment/12745290/YARN-2410-v2.patch |
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / 4084eaf |
| Console output | 
https://builds.apache.org/job/PreCommit-YARN-Build/8533/console |


This message was automatically generated.

> 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
>             Fix For: 2.7.2
>
>         Attachments: YARN-2410-v1.patch, YARN-2410-v2.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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