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From "Sunil G (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-4280) CapacityScheduler reservations may not prevent indefinite postponement on a busy cluster
Date Wed, 22 Jun 2016 18:01:16 GMT

    [ https://issues.apache.org/jira/browse/YARN-4280?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15344888#comment-15344888
] 

Sunil G commented on YARN-4280:
-------------------------------

Thanks [~kshukla] for the patch and its an interesting problem.

I have one doubt here.
One queue is under served and it has  a single pending demand for 8GB (but there is no headroom).
If this request is served, then this queue will no longer be underserved. There are other
queues and has pending demands for 2GB. With this approach, I think allocations will be skipped
for other queues untill this 8GB is served. I might be missing something here, pls help to
correct me if I m wrong.

> CapacityScheduler reservations may not prevent indefinite postponement on a busy cluster
> ----------------------------------------------------------------------------------------
>
>                 Key: YARN-4280
>                 URL: https://issues.apache.org/jira/browse/YARN-4280
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacity scheduler
>    Affects Versions: 2.6.1, 2.8.0, 2.7.1
>            Reporter: Kuhu Shukla
>            Assignee: Kuhu Shukla
>         Attachments: YARN-4280.001.patch, YARN-4280.002.patch, YARN-4280.003.patch, YARN-4280.004.patch
>
>
> Consider the following scenario:
> There are 2 queues A(25% of the total capacity) and B(75%), both can run at total cluster
capacity. There are 2 applications, appX that runs on Queue A, always asking for 1G containers(non-AM)
and appY runs on Queue B asking for 2 GB containers.
> The user limit is high enough for the application to reach 100% of the cluster resource.

> appX is running at total cluster capacity, full with 1G containers releasing only one
container at a time. appY comes in with a request of 2GB container but only 1 GB is free.
Ideally, since appY is in the underserved queue, it has higher priority and should reserve
for its 2 GB request. Since this request puts the alloc+reserve above total capacity of the
cluster, reservation is not made. appX comes in with a 1GB request and since 1GB is still
available, the request is allocated. 
> This can continue indefinitely causing priority inversion.



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