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https://issues.apache.org/jira/browse/YARN-3508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14574935#comment-14574935
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Jian He commented on YARN-3508:
-------------------------------

I think this make sense to move preemption events from main dispatcher to the 
scheduler dispatcher. Otherwise, any non-scheduler events on main dispatcher 
will be waiting for the preemption events to grab the scheduler lock, which is 
unnecessary. 

> Preemption processing occuring on the main RM dispatcher
> --------------------------------------------------------
>
>                 Key: YARN-3508
>                 URL: https://issues.apache.org/jira/browse/YARN-3508
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: resourcemanager, scheduler
>    Affects Versions: 2.6.0
>            Reporter: Jason Lowe
>            Assignee: Varun Saxena
>         Attachments: YARN-3508.002.patch, YARN-3508.01.patch
>
>
> We recently saw the RM for a large cluster lag far behind on the 
> AsyncDispacher event queue.  The AsyncDispatcher thread was consistently 
> blocked on the highly-contended CapacityScheduler lock trying to dispatch 
> preemption-related events for RMContainerPreemptEventDispatcher.  Preemption 
> processing should occur on the scheduler event dispatcher thread or a 
> separate thread to avoid delaying the processing of other events in the 
> primary dispatcher queue.



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