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https://issues.apache.org/jira/browse/YARN-4287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14980886#comment-14980886
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MENG DING commented on YARN-4287:
---------------------------------
Looking at this issue, I have to admit that I had been frustrated with the
existing {{getLocalityWaitFactor}}, and had the same question as [~nroberts]:
bq. This made no sense to me - Accept OFF-SWITCH without delay, yet don't
accept RACK-LOCAL??
IMHO, although it makes sense to introduce a configurable rack-locality delay,
it doesn't help when the cluster is really busy as described in YARN-4189 and
YARN-3309. As an interim solution, I am in favor of the
YARN-4287-minimal.patch, but I think the default configuration of
DEFAULT_RACK_LOCALITY_FULL_RESET should be set to true to be backward
compatible.
> 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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