[jira] [Commented] (MAPREDUCE-6541) Exclude scheduled reducer memory when calculating available mapper slots from headroom to avoid deadlock

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

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6541?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14996998#comment-14996998 ] 

Wangda Tan commented on MAPREDUCE-6541:
---------------------------------------

[~varun_saxena], yes you're correct, updated title/desc.

Thanks,

> Exclude scheduled reducer memory when calculating available mapper slots from headroom to avoid deadlock 
> ---------------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-6541
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6541
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Wangda Tan
>            Assignee: Varun Saxena
>
> We saw a MR deadlock recently:
> - When NM restarted by framework without enable recovery, containers running on these nodes will be identified as "ABORTED", and MR AM will try to reschedule "ABORTED" mapper containers.
> - Since such lost mappers are "ABORTED" container, MR AM gives normal mapper priority (priority=20) to such mapper requests. If there's any pending reducer (priority=10) at the same time, mapper requests need to wait for reducer requests satisfied.
> - In our test, one mapper needs 700+ MB, reducer needs 1000+ MB, and RM available resource = mapper-request = (700+ MB), only one job was running in the system so scheduler cannot allocate more reducer containers AND MR-AM thinks there're enough headroom for mapper so reducer containers will not be preempted.
> MAPREDUCE-6302 can solve most of the problems, but in the other hand, I think we may need to exclude scheduled reducers resource when calculating #available-mapper-slots from headroom. Which we can avoid excessive reducer preemption.



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