Craig Welch commented on YARN-1198:

Sorry, the above was off - the conversation happened offline, here was the 
tweak to .7 that Jian suggested:

Hi Craig, I looked at your patch again. It's similar to what I thought. One 
thing is that now that headRoom is not application specific, it doesn't belong 
to application any more. We may make a member of LeafQueue#User. From 
CapacityScheduler#allocate, directly call LeafQueue #getAndCalculateHeadRoom , 
not going through SchedulerApplicationAttempt route to get the HeadRoom. I 
think this is simpler. do you think this will work?

> We may make a member of LeafQueue#User. To clarify: make the headRoom a 
> variable of LeafQueue#User, and remove that from SchedulerAttempt

we might, in this approach, do what we are doing in .7 but without the 
HeadroomProvider at all... I'm going to give a go at this...

> Capacity Scheduler headroom calculation does not work as expected
> -----------------------------------------------------------------
>                 Key: YARN-1198
>                 URL: https://issues.apache.org/jira/browse/YARN-1198
>             Project: Hadoop YARN
>          Issue Type: Bug
>            Reporter: Omkar Vinit Joshi
>            Assignee: Craig Welch
>         Attachments: YARN-1198.1.patch, YARN-1198.2.patch, YARN-1198.3.patch, 
> YARN-1198.4.patch, YARN-1198.5.patch, YARN-1198.6.patch, YARN-1198.7.patch, 
> YARN-1198.8.patch
> Today headroom calculation (for the app) takes place only when
> * New node is added/removed from the cluster
> * New container is getting assigned to the application.
> However there are potentially lot of situations which are not considered for 
> this calculation
> * If a container finishes then headroom for that application will change and 
> should be notified to the AM accordingly.
> * If a single user has submitted multiple applications (app1 and app2) to the 
> same queue then
> ** If app1's container finishes then not only app1's but also app2's AM 
> should be notified about the change in headroom.
> ** Similarly if a container is assigned to any applications app1/app2 then 
> both AM should be notified about their headroom.
> ** To simplify the whole communication process it is ideal to keep headroom 
> per User per LeafQueue so that everyone gets the same picture (apps belonging 
> to same user and submitted in same queue).
> * If a new user submits an application to the queue then all applications 
> submitted by all users in that queue should be notified of the headroom 
> change.
> * Also today headroom is an absolute number ( I think it should be normalized 
> but then this is going to be not backward compatible..)
> * Also  when admin user refreshes queue headroom has to be updated.
> These all are the potential bugs in headroom calculations

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