[jira] [Created] (YARN-2410) Nodemanager ShuffleHandler can easily exhaust file descriptors

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

Nathan Roberts created YARN-2410:
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             Summary: 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
            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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