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From "Eric Payne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-4606) CapacityScheduler: applications could get starved because computation of #activeUsers considers pending apps
Date Mon, 07 May 2018 16:44:02 GMT

    [ https://issues.apache.org/jira/browse/YARN-4606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16466136#comment-16466136

Eric Payne commented on YARN-4606:

Thanks [~manirajv06@gmail.com] for your consistent and continuing efforts to fix this problem.

I am doing an in-depth review, but I would like to address a few things first regarding method
names and comments. I feel that it is important to be accurate in these areas in order to
eliminate confusion for those maintaining this code.

- All occurrences of "atleast" should be "at least"
- Comment for {{AbstractUsersManager#getNumActiveUsers}}:
-   * Get number of active users i.e. users with applications which have pending
-   * resource requests.
+   * Get number of active users i.e. users with atleast 1 active applications
For this comment, I would say "Get number of active users i.e. users with at least 1 running
application and and applications requesting resources"
- I would prefer it if the name of {{ActiveUsersOfPendingApps}} was changed everywhere to
{{ActiveUsersWithOnlyPendingApps}}. This is kind of a nit, but I do feel that the rename would
be more descriptive.
- {{AbstractUsersManager#incrNumActiveUsersOfPendingApps}}, {{decrNumActiveUsersOfPendingApps}},
and {{getNumActiveUsersOfPendingApps}}
Change description to "number of users with only pending apps"
- {{UsersManager#activateApplication}} and {{deactivateApplication}}
Change "Active users which has atleast 1 pending apps:" to "Active users which have at least
1 pending app:"

> 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,
> 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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