[jira] [Commented] (YARN-3243) CapacityScheduler should pass headroom from parent to children to make sure ParentQueue obey its capacity limits.

["Thomas Graves (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/YARN-3243?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14521580#comment-14521580 ] 

Thomas Graves commented on YARN-3243:
-------------------------------------

[~leftnoteasy] Can we pull this back into the branch-2.7?  

> CapacityScheduler should pass headroom from parent to children to make sure ParentQueue obey its capacity limits.
> -----------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-3243
>                 URL: https://issues.apache.org/jira/browse/YARN-3243
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacityscheduler, resourcemanager
>            Reporter: Wangda Tan
>            Assignee: Wangda Tan
>             Fix For: 2.8.0
>
>         Attachments: YARN-3243.1.patch, YARN-3243.2.patch, YARN-3243.3.patch, YARN-3243.4.patch, YARN-3243.5.patch
>
>
> Now CapacityScheduler has some issues to make sure ParentQueue always obeys its capacity limits, for example:
> 1) When allocating container of a parent queue, it will only check parentQueue.usage < parentQueue.max. If leaf queue allocated a container.size > (parentQueue.max - parentQueue.usage), parent queue can excess its max resource limit, as following example:
> {code}
>         A  (usage=54, max=55)
>        /     \
>       A1     A2 (usage=1, max=55)
> (usage=53, max=53)
> {code}
> Queue-A2 is able to allocate container since its usage < max, but if we do that, A's usage can excess A.max.
> 2) When doing continous reservation check, parent queue will only tell children "you need unreserve *some* resource, so that I will less than my maximum resource", but it will not tell how many resource need to be unreserved. This may lead to parent queue excesses configured maximum capacity as well.
> With YARN-3099/YARN-3124, now we have {{ResourceUsage}} class in each class, *here is my proposal*:
> - ParentQueue will set its children's ResourceUsage.headroom, which means, *maximum resource its children can allocate*.
> - ParentQueue will set its children's headroom to be (saying parent's name is "qA"): min(qA.headroom, qA.max - qA.used). This will make sure qA's ancestors' capacity will be enforced as well (qA.headroom is set by qA's parent).
> - {{needToUnReserve}} is not necessary, instead, children can get how much resource need to be unreserved to keep its parent's resource limit.
> - More over, with this, YARN-3026 will make a clear boundary between LeafQueue and FiCaSchedulerApp, headroom will consider user-limit, etc.



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