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https://issues.apache.org/jira/browse/YARN-2008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14068024#comment-14068024
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Craig Welch commented on YARN-2008:
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Hmm, I don't think that we can change headroom to be just the guaranteed or
base capacity because I believe that will defeat the support for having a max
capacity above the base capacity. As I understand it that is in place so that
busy queues can grow to use more of the cluster when other queues are
underutilized - to achieve more efficient and full use of the cluster overall -
and if the application gets the low baseline headroom it will not be able to
effectively use that greater capacity. Assuming we keep support for the max
capacity, then even with pre-emption I think we will need this logic, because
preemption won't guarantee that all the queues have their max capacity
available to them, as the total max capacity can be over 100%. Preemption will
help, certainly, but I don't think it can replace this logic - I think we need
both.
> CapacityScheduler may report incorrect queueMaxCap if there is hierarchy
> queue structure
> -----------------------------------------------------------------------------------------
>
> Key: YARN-2008
> URL: https://issues.apache.org/jira/browse/YARN-2008
> Project: Hadoop YARN
> Issue Type: Sub-task
> Affects Versions: 2.3.0
> Reporter: Chen He
> Assignee: Chen He
> Attachments: YARN-2008.1.patch, YARN-2008.2.patch
>
>
> If there are two queues, both allowed to use 100% of the actual resources in
> the cluster. Q1 and Q2 currently use 50% of actual cluster's resources and
> there is not actual space available. If we use current method to get
> headroom, CapacityScheduler thinks there are still available resources for
> users in Q1 but they have been used by Q2.
> If the CapacityScheduelr has a hierarchy queue structure, it may report
> incorrect queueMaxCap. Here is a example
> || ||rootQueue|| ||
> | | / |
> \ |
> | L1ParentQueue1 | |
> L1ParentQueue2 |
> | (allowed to use up 80% of its parent) | | (allowed to use 20%
> in minimum of its parent)|
> | / | \ | |
> | L2LeafQueue1 | L2LeafQueue2 | |
> |(50% of its parent) | (50% of its parent in minimum) | |
> When we calculate headroom of a user in L2LeafQueue2, current method will
> think L2LeafQueue2 can use 40% (80%*50%) of actual rootQueue resources.
> However, without checking L1ParentQueue1, we are not sure. It is possible
> that L1ParentQueue2 have used 40% of rootQueue resources right now. Actually,
> L2LeafQueue2 can only use 30% (60%*50%).
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