[jira] [Commented] (MAPREDUCE-6501) Improve reducer preemption

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

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15435690#comment-15435690 ] 

Haibo Chen commented on MAPREDUCE-6501:
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Task 2 is already implemented with taskAttemptProgress, that is, SHUFFLE phase is expressed in terms of progress, and preemption also tries to preempt reducers that are of least progress.
Task 3 is inapplicable since reducer preemption never kicks in if there is one mapper can run.

> Improve reducer preemption
> --------------------------
>
>                 Key: MAPREDUCE-6501
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6501
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: applicationmaster
>    Affects Versions: 2.7.1
>            Reporter: Karthik Kambatla
>            Assignee: Haibo Chen
>
> As discussed on MAPREDUCE-6302, we could improve the reducer preemption as follows:
> # preempt enough reducers so there are enough mappers to match slowstart 
> # prioritize preempting reducers that are still in SHUFFLE phase
> # add an option to not preempt reducers that are past SHUFFLE phase irrespective of slowstart as long as one mapper can run
> We could do it all in one patch or create subtasks as necessary. 



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