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https://issues.apache.org/jira/browse/YARN-2990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14280238#comment-14280238
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Karthik Kambatla commented on YARN-2990:
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Handling rack-local requests the same way could be much more involved than 
handling off-switch requests. ResourceRequest has hostName, the RM/scheduler 
has mapping of NodeId -> SchedulerNode. Checking whether the hostName 
corresponds to a node or rack can't be achieved through a simple 
map.containsKey() and requires iterating through all racks/nodes which can be 
quite expensive.

How about we handle off-switch requests here and work on the rack-local 
requests in a follow-up JIRA? This lets us take care of the AM container which 
is very common. 


> FairScheduler's delay-scheduling always waits for node-local and rack-local 
> delays, even for off-rack-only requests
> -------------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-2990
>                 URL: https://issues.apache.org/jira/browse/YARN-2990
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: fairscheduler
>    Affects Versions: 2.6.0
>            Reporter: Karthik Kambatla
>            Assignee: Karthik Kambatla
>         Attachments: yarn-2990-0.patch, yarn-2990-test.patch
>
>
> Looking at the FairScheduler, it appears the node/rack locality delays are 
> used for all requests, even those that are only off-rack. 
> More details in comments. 



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