Sandy Ryza commented on YARN-2430:

I believe #3 is the best approach as it's more performant than #1 and #2 has 
correctness issues.  I actually implemented it a little while ago as part of 
YARN-1297 and will try to get that in.

> FairShareComparator: cache the results of getResourceUsage()
> ------------------------------------------------------------
>                 Key: YARN-2430
>                 URL: https://issues.apache.org/jira/browse/YARN-2430
>             Project: Hadoop YARN
>          Issue Type: Improvement
>            Reporter: Maysam Yabandeh
>            Assignee: Maysam Yabandeh
> The compare of FairShareComparator has 3 invocation of  getResourceUsage per 
> comparable object. In the case of queues, the implementation of 
> getResourceUsage requires iterating over the apps and adding up their current 
> usage. The compare method can reuse the result of getResourceUsage to reduce 
> the load by third. However, to further reduce the load the result of 
> getResourceUsage can be cached in FSLeafQueue. This would be more efficient 
> since the invocation of compare method on each Comparable object is >= 1.

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