Wangda Tan commented on YARN-2022:

I've revisited code,
(1) getMaxAMResourcePerQueuePercent with getAbsoluteMaximumCapacity is used to 
check if an app can be active when considering total #application within a 
(2) getMaxAMResourcePerQueuePercent with getAbsoluteCapacity is used to check 
if an app can be active when considering total #application under a user within 
a queue.

bq. Could I go along by changing maxAMCapacity w.r.t getAbsoluteCapacity?
IMO, I'd prefer use (1) instead of (2). And (2) can be used when we considering 
user-limit when do preemption, which is the scope of YARN-2069.

And I think [~sunilg]'s solution should be correct.

> Preempting an Application Master container can be kept as least priority when 
> multiple applications are marked for preemption by 
> ProportionalCapacityPreemptionPolicy
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------
>                 Key: YARN-2022
>                 URL: https://issues.apache.org/jira/browse/YARN-2022
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: resourcemanager
>    Affects Versions: 2.4.0
>            Reporter: Sunil G
>            Assignee: Sunil G
>         Attachments: YARN-2022-DesignDraft.docx, YARN-2022.2.patch, 
> YARN-2022.3.patch, YARN-2022.4.patch, YARN-2022.5.patch, YARN-2022.6.patch, 
> YARN-2022.7.patch, Yarn-2022.1.patch
> Cluster Size = 16GB [2NM's]
> Queue A Capacity = 50%
> Queue B Capacity = 50%
> Consider there are 3 applications running in Queue A which has taken the full 
> cluster capacity. 
> J1 = 2GB AM + 1GB * 4 Maps
> J2 = 2GB AM + 1GB * 4 Maps
> J3 = 2GB AM + 1GB * 2 Maps
> Another Job J4 is submitted in Queue B [J4 needs a 2GB AM + 1GB * 2 Maps ].
> Currently in this scenario, Jobs J3 will get killed including its AM.
> It is better if AM can be given least priority among multiple applications. 
> In this same scenario, map tasks from J3 and J2 can be preempted.
> Later when cluster is free, maps can be allocated to these Jobs.

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