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https://issues.apache.org/jira/browse/YARN-1959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13974456#comment-13974456
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Sandy Ryza commented on YARN-1959:
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One thing I don't understand from reading the Capacity Scheduler headroom
calculation is how it prevents apps from starving when a max capacity isn't
set. It's defined as min((userLimit, queue-max-cap) - consumed). If no max
capacities are set and two users are running in a queue, each taking up half
the queue's capacity, the headroom for each user will be half the queue's
capacity. If the cluster is saturated to the extent that the queue's usage
can't go above its capacity, the headroom is being vastly overreported.
[~jlowe], any insight on this?
> Fix headroom calculation in Fair Scheduler
> ------------------------------------------
>
> Key: YARN-1959
> URL: https://issues.apache.org/jira/browse/YARN-1959
> Project: Hadoop YARN
> Issue Type: Bug
> Reporter: Sandy Ryza
>
> The Fair Scheduler currently always sets the headroom to 0.
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