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From "Manikandan R (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-4606) CapacityScheduler: applications could get starved because computation of #activeUsers considers pending apps
Date Tue, 30 Jan 2018 18:08:00 GMT

    [ https://issues.apache.org/jira/browse/YARN-4606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16345536#comment-16345536

Manikandan R commented on YARN-4606:

[~leftnoteasy] Based on my understanding, as of now {{ActiveUsersManager#getNumActiveUsers}}
has been used only in {{LeafQueue#getUserAMResourceLimitPerPartition}} to compute the userAMLimit.
Given this, ensuring active users count increments only after app activation is sufficient
to fix this JIRA? Something like,

 1. Introduce a new method {{activeApplication()}} in {{AppSchedulingInfo}} to set new private
boolean variable "isActivated" to true.
 2. Call #1 from {{LeafQueue#activateApplications}} after {{application.updateAMContainerDiagnostics(AMState.ACTIVATED,
null);}} similar to changes in earlier POC patch.
 3. Ensure {{abstractUsersManager.activateApplication(user, applicationId);}} in {{AppSchedulingInfo#updatePendingResources}}
executes only when isActivate is true.

Please share your views.

> 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: Wangda Tan
>            Priority: Critical
>         Attachments: YARN-4606.1.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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