Wangda Tan commented on YARN-3298:

I think I got your point now. Yes, as you said, if we enforce the limit (used + 
requred <= user-limit), and don't change the user-limit computation, queue 
cannot over its configured capacity.

Originally, this ticket trying to solve the jitter problem when we have the 
YARN-2069. However, YARN-2069 will only take effect when queue becomes 
over-satisfied, at that time, CS will not give queue more resources. So the 
jitter won't happen actually.

Jitter will happen when we have YARN-2113 (preemption will happen to balance 
usage between users when queue doesn't over its capacity), at that time, 
user-limit enforcement should be done.

Basically, I agree with your method, which is {{current_capacity = 
max(queue.used,queue.capacity)+now_required}}, it can solve the queue cannot 
over its configured capacity problem, but it seems not necessary at least for 
now. We can delay this change until YARN-2113 is required.



> User-limit should be enforced in CapacityScheduler
> --------------------------------------------------
>                 Key: YARN-3298
>                 URL: https://issues.apache.org/jira/browse/YARN-3298
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacityscheduler, yarn
>            Reporter: Wangda Tan
>            Assignee: Wangda Tan
> User-limit is not treat as a hard-limit for now, it will not consider 
> required-resource (resource of being-allocated resource request). And also, 
> when user's used resource equals to user-limit, it will still continue. This 
> will generate jitter issues when we have YARN-2069 (preemption policy kills a 
> container under an user, and scheduler allocate a container under the same 
> user soon after).
> The expected behavior should be as same as queue's capacity:
> Only when user.usage + required <= user-limit (1), queue will continue to 
> allocate container.
> (1), user-limit mentioned here is determined by following computing
> {code}
> current-capacity = queue.used + now-required (when queue.used > 
> queue.capacity)
>                    queue.capacity (when queue.used < queue.capacity)
> user-limit = min(max(current-capacity / #active-users, current-capacity * 
> user-limit / 100), queue-capacity * user-limit-factor)
> {code}

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