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https://issues.apache.org/jira/browse/YARN-2009?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15504991#comment-15504991
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Wangda Tan commented on YARN-2009:
----------------------------------

And one additional note about why balancing user-usage only in preemption logic 
will cause excessive preemption.

Continue above 3-users example.

If the preemption policy compute and set 4 (4 = 12 / 3) for ideal allocation of 
user A/B/C. So it may preempt some resource from A/B to make room for C. But 
when scheduler doing allocation. because A/B sit in front of the queue, 
resource will come back to A/B again.


> Priority support for preemption in ProportionalCapacityPreemptionPolicy
> -----------------------------------------------------------------------
>
>                 Key: YARN-2009
>                 URL: https://issues.apache.org/jira/browse/YARN-2009
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: capacityscheduler
>            Reporter: Devaraj K
>            Assignee: Sunil G
>         Attachments: YARN-2009.0001.patch
>
>
> While preempting containers based on the queue ideal assignment, we may need 
> to consider preempting the low priority application containers first.



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