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https://issues.apache.org/jira/browse/YARN-4287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14979560#comment-14979560
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Wangda Tan commented on YARN-4287:
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Hi [~nroberts],
bq. One argument for sticking with the scaling approach is the fact that we
basically do it today in a simpler fashion. If you specify node-locality-delay
of 5000 on a 3000 node cluster, it gets automatically scaled down to 3000
without informing the user. So I'd say scale it but don't try to explain it in
user documentation.
I still think scaling down is not a straightforward way to support the problem
you mentioned (user isn't clear about size of cluster). Instead, I think we can
use percentage. User can say, I want node locality delay to 300 OR 10% of
cluster size. And same to rack locality delay. Scheduler will compute what's
the actual delay at runtime. With this, I think we can safely cap delay by
cluster size. Does this make sense to you?
Thanks,
> Capacity Scheduler: Rack Locality improvement
> ---------------------------------------------
>
> Key: YARN-4287
> URL: https://issues.apache.org/jira/browse/YARN-4287
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: capacityscheduler
> Affects Versions: 2.7.1
> Reporter: Nathan Roberts
> Assignee: Nathan Roberts
> Attachments: YARN-4287-minimal.patch, YARN-4287-v2.patch,
> YARN-4287-v3.patch, YARN-4287-v4.patch, YARN-4287.patch
>
>
> YARN-4189 does an excellent job describing the issues with the current delay
> scheduling algorithms within the capacity scheduler. The design proposal also
> seems like a good direction.
> This jira proposes a simple interim solution to the key issue we've been
> experiencing on a regular basis:
> - rackLocal assignments trickle out due to nodeLocalityDelay. This can have
> significant impact on things like CombineFileInputFormat which targets very
> specific nodes in its split calculations.
> I'm not sure when YARN-4189 will become reality so I thought a simple interim
> patch might make sense. The basic idea is simple:
> 1) Separate delays for rackLocal, and OffSwitch (today there is only 1)
> 2) When we're getting rackLocal assignments, subsequent rackLocal assignments
> should not be delayed
> Patch will be uploaded shortly. No big deal if the consensus is to go
> straight to YARN-4189.
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