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https://issues.apache.org/jira/browse/YARN-9770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16917958#comment-16917958
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Jonathan Hung commented on YARN-9770:
-------------------------------------

I see, thanks [~leftnoteasy] for the comments. I think in practice A may be 
able to recover some of its preempted resources, but some of it will be 
acquired by B.

Also as long as we keep default queue ordering policy 
QUEUE_UTILIZATION_ORDERING_POLICY, underutilized queues should still be able to 
quickly acquire resources from preempted queues.

Thoughts on this?

> Create a queue ordering policy which picks child queues with equal probability
> ------------------------------------------------------------------------------
>
>                 Key: YARN-9770
>                 URL: https://issues.apache.org/jira/browse/YARN-9770
>             Project: Hadoop YARN
>          Issue Type: Improvement
>            Reporter: Jonathan Hung
>            Assignee: Jonathan Hung
>            Priority: Major
>              Labels: release-blocker
>         Attachments: YARN-9770.001.patch, YARN-9770.002.patch, 
> YARN-9770.003.patch
>
>
> Ran some simulations with the default queue_utilization_ordering_policy:
> An underutilized queue which receives an application with many (thousands) 
> resource requests will hog scheduler allocations for a long time (on the 
> order of a minute). In the meantime apps are getting submitted to all other 
> queues, which increases activeUsers in these queues, which drops user limit 
> in these queues to small values if minimum-user-limit-percent is configured 
> to small values (e.g. 10%).
> To avoid this issue, we assign to queues with equal probability, to avoid 
> scenarios where queues don't get allocations for a long time.



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