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From "Jason Lowe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-6689) MapReduce job can infinitely increase number of reducer resource requests
Date Fri, 06 May 2016 16:09:13 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15274277#comment-15274277
] 

Jason Lowe commented on MAPREDUCE-6689:
---------------------------------------

+1 lgtm.  Will commit this later today if there are no objections.

> MapReduce job can infinitely increase number of reducer resource requests
> -------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-6689
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6689
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Wangda Tan
>            Assignee: Wangda Tan
>            Priority: Blocker
>         Attachments: MAPREDUCE-6689.1.patch
>
>
> We have seen this issue from one of our clusters: when running terasort map-reduce job,
some mappers failed after reducer started, and then MR AM tries to preempt reducers to schedule
these failed mappers.
> After that, MR AM enters an infinite loop, for every RMContainerAllocator#heartbeat run,
it:
> - In {{preemptReducesIfNeeded}}, it cancels all scheduled reducer requests. (total scheduled
reducers = 1024)
> - Then, in {{scheduleReduces}}, it ramps up all reducers (total = 1024).
> As a result, we can see total #requested-containers increased 1024 for every MRAM-RM
heartbeat (1 sec per heartbeat). The AM is hanging for 18+ hours, so we get 18 * 3600 * 1024
~ 66M+ requested containers in RM side.
> And this bug also triggered YARN-4844, which makes RM stop scheduling anything.
> Thanks to [~sidharta-s] for helping with analysis. 



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