Jason Lowe commented on YARN-4165:

Something must be amiss then, since the capacity scheduler should not be making 
reservations when the node has insufficient memory to ever fill the request 
after YARN-957.

As for reservations in general, the capacity scheduler applies reservations 
against the user limits within the queue.  If the user has the ability to fully 
use the queue then yes, reservations can stall other applications within the 
queue since the user is allowed to fill the queue.  Without that behavior the 
application with large requests could end up in a situation where it never runs 
due to indefinite postponement problems.

> An outstanding container request makes all nodes to be reserved causing all 
> jobs pending
> ----------------------------------------------------------------------------------------
>                 Key: YARN-4165
>                 URL: https://issues.apache.org/jira/browse/YARN-4165
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: capacity scheduler, resourcemanager, scheduler
>    Affects Versions: 2.7.1
>            Reporter: Weiwei Yang
>            Assignee: Weiwei Yang
> We have a long running service in YARN, it has a outstanding container 
> request that YARN cannot satisfy (require more memory that nodemanager can 
> supply). Then YARN reserves all nodes for this application, when I submit 
> other jobs (require relative small memory that nodemanager can supply), all 
> jobs are pending because YARN skips scheduling containers on the nodes that 
> have been reserved.

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