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https://issues.apache.org/jira/browse/YARN-4606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16466541#comment-16466541
 ] 

Eric Payne commented on YARN-4606:
----------------------------------

{code:title=AppSchedulingInfo#updatePendingResources}
if(! hasActiveUsersOfPendingAppsDecremented.get()) {
    abstractUsersManager.decrNumActiveUsersOfPendingApps();
    hasActiveUsersOfPendingAppsDecremented.set(true);
}
{code}

Does {{hasActiveUsersOfPendingAppsDecremented}} need to be atomic? What is the 
benefit?

> CapacityScheduler: applications could get starved because computation of 
> #activeUsers considers pending apps 
> -------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-4606
>                 URL: https://issues.apache.org/jira/browse/YARN-4606
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacity scheduler, capacityscheduler
>    Affects Versions: 2.8.0, 2.7.1
>            Reporter: Karam Singh
>            Assignee: Manikandan R
>            Priority: Critical
>         Attachments: YARN-4606.001.patch, YARN-4606.1.poc.patch, 
> YARN-4606.POC.2.patch, YARN-4606.POC.patch
>
>
> Currently, if all applications belong to same user in LeafQueue are pending 
> (caused by max-am-percent, etc.), ActiveUsersManager still considers the user 
> is an active user. This could lead to starvation of active applications, for 
> example:
> - App1(belongs to user1)/app2(belongs to user2) are active, app3(belongs to 
> user3)/app4(belongs to user4) are pending
> - ActiveUsersManager returns #active-users=4
> - However, there're only two users (user1/user2) are able to allocate new 
> resources. So computed user-limit-resource could be lower than expected.



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