Wangda Tan commented on YARN-3434:

bq. All you would be using it for is passing it down to assignContainer and 
then it would be out of date. If someone else started looking at that value 
assuming it was up to date then it would be wrong (unless of course we started 
updating it as stated above). But it would only be for a single user, not all 
users unless again we changed to calculate for every user whenever something 
changed. That seems a bit excessive.
To clarify, ResourceLimits is the bridge between parent and child, parent will 
tell child "hey, this is the limit you can use", LeafQueue will do the same 
thing to app, ParentQueue doesn't compute/pass-down user-limit to LeafQueue at 
all, LeafQueue will do that and make sure it get updated for every allocation.

> Interaction between reservations and userlimit can result in significant ULF 
> violation
> --------------------------------------------------------------------------------------
>                 Key: YARN-3434
>                 URL: https://issues.apache.org/jira/browse/YARN-3434
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacityscheduler
>    Affects Versions: 2.6.0
>            Reporter: Thomas Graves
>            Assignee: Thomas Graves
>         Attachments: YARN-3434.patch
> ULF was set to 1.0
> User was able to consume 1.4X queue capacity.
> It looks like when this application launched, it reserved about 1000 
> containers, each 8G each, within about 5 seconds. I think this allowed the 
> logic in assignToUser() to allow the userlimit to be surpassed.

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