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https://issues.apache.org/jira/browse/YARN-6344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15957849#comment-15957849
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Jason Lowe commented on YARN-6344:
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I'd prefer a configured rack locality delay of zero means no additional rack
delay, but I see that is semantically different than disabling it altogether.
Specifying a rack locality delay of zero means it will _not_ scale the node
locality delay based on the request/cluster sizes like it does today, whereas
setting it to -1 will. In that sense it's not purely an additional delay.
Given I don't know the complete backstory on the reasoning behind why it
behaves the way it does for node locality delay, I can see the desire to leave
the existing behavior unchanged when this new setting isn't configured.
Patch looks good to me.
> Rethinking OFF_SWITCH locality in CapacityScheduler
> ---------------------------------------------------
>
> Key: YARN-6344
> URL: https://issues.apache.org/jira/browse/YARN-6344
> Project: Hadoop YARN
> Issue Type: Bug
> Components: capacityscheduler
> Reporter: Konstantinos Karanasos
> Assignee: Konstantinos Karanasos
> Attachments: YARN-6344.001.patch, YARN-6344.002.patch,
> YARN-6344.003.patch, YARN-6344.004.patch
>
>
> When relaxing locality from node to rack, the {{node-locality-parameter}} is
> used: when scheduling opportunities for a scheduler key are more than the
> value of this parameter, we relax locality and try to assign the container to
> a node in the corresponding rack.
> On the other hand, when relaxing locality to off-switch (i.e., assign the
> container anywhere in the cluster), we are using a {{localityWaitFactor}},
> which is computed based on the number of outstanding requests for a specific
> scheduler key, which is divided by the size of the cluster.
> In case of applications that request containers in big batches (e.g.,
> traditional MR jobs), and for relatively small clusters, the
> localityWaitFactor does not affect relaxing locality much.
> However, in case of applications that request containers in small batches,
> this load factor takes a very small value, which leads to assigning
> off-switch containers too soon. This situation is even more pronounced in big
> clusters.
> For example, if an application requests only one container per request, the
> locality will be relaxed after a single missed scheduling opportunity.
> The purpose of this JIRA is to rethink the way we are relaxing locality for
> off-switch assignments.
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