[jira] [Commented] (MAPREDUCE-6474) ShuffleHandler can possibly exhaust nodemanager file descriptors

["Hudson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6474?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14739033#comment-14739033 ] 

Hudson commented on MAPREDUCE-6474:
-----------------------------------

FAILURE: Integrated in Hadoop-trunk-Commit #8429 (See [https://builds.apache.org/job/Hadoop-trunk-Commit/8429/])
MAPREDUCE-6474. ShuffleHandler can possibly exhaust nodemanager file descriptors. Contributed by Kuhu Shukla (jlowe: rev 8e615588d5216394d0251a9c97bd706537856c6d)
* hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/main/java/org/apache/hadoop/mapred/ShuffleHandler.java
* hadoop-mapreduce-project/CHANGES.txt
* hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-shuffle/src/test/java/org/apache/hadoop/mapred/TestShuffleHandler.java


> 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
>             Fix For: 2.7.2
>
>         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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