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Date: Fri, 25 Jul 2014 16:40:40 +0000 (UTC)
From: "Ashwin Shankar (JIRA)" <jira@apache.org>
To: yarn-issues@hadoop.apache.org
Message-ID: <JIRA.12723751.1403731756885.45576.1406306440171@arcas>
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Subject: [jira] [Commented] (YARN-2214) FairScheduler:
 preemptContainerPreCheck() in FSParentQueue delays convergence towards
 fairness
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    [ https://issues.apache.org/jira/browse/YARN-2214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14074548#comment-14074548 ] 

Ashwin Shankar commented on YARN-2214:
--------------------------------------

Thanks Karthik !

> FairScheduler: preemptContainerPreCheck() in FSParentQueue delays convergence towards fairness
> ----------------------------------------------------------------------------------------------
>
>                 Key: YARN-2214
>                 URL: https://issues.apache.org/jira/browse/YARN-2214
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: scheduler
>    Affects Versions: 2.5.0
>            Reporter: Ashwin Shankar
>            Assignee: Ashwin Shankar
>             Fix For: 2.6.0
>
>         Attachments: YARN-2214-v1.txt, YARN-2214-v2.txt
>
>
> preemptContainerPreCheck() in FSParentQueue rejects preemption requests if the parent queue is below fair share. This can cause a delay in converging towards fairness when the starved leaf queue and the queue above fairshare belong under a non-root parent queue(ie their least common ancestor is a parent queue which is not root).
> Here is an example :
> root.parent has fair share = 80% and usage = 80%
> root.parent.child1 has fair share =40% usage = 80%
> root.parent.child2 has fair share=40% usage=0%
> Now a job is submitted to child2 and the demand is 40%.
> Preemption will kick in and try to reclaim all the 40% from child1.
> When it preempts the first container from child1,the usage of root.parent will become <80%, which is less than root.parent's fair share,causing preemption to stop.So only one container gets preempted in this round although the need is a lot more. child2 would eventually get to half its fair share but only after multiple rounds of preemption.
> Solution is to remove preemptContainerPreCheck() in FSParentQueue and keep it only in FSLeafQueue(which is already there).


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