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From "jay vyas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-2410) Nodemanager ShuffleHandler can easily exhaust file descriptors
Date Wed, 13 Aug 2014 18:08:17 GMT

    [ https://issues.apache.org/jira/browse/YARN-2410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14095824#comment-14095824
] 

jay vyas commented on YARN-2410:
--------------------------------

Adding this as a part of BIGTOP-1403 also.  hopefully we can have some smoke tests which induce
this bug.  

If you have a code snippet or patch to contribute that generates this , feel free to attach
it there, we can help you to refine it.

> Nodemanager ShuffleHandler can easily 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: Chen He
>            Priority: Critical
>
> 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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