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https://issues.apache.org/jira/browse/YARN-6344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15926830#comment-15926830
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Konstantinos Karanasos edited comment on YARN-6344 at 3/15/17 9:41 PM:
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The described issue was observed together with [~asuresh] and [~curino], while
examining some of our internal applications that request containers in small
batches.
We also brought it to the attention of [~jlowe].
One way to solve the problem is to introduce an additional parameter, namely
{{rack-locality-delay}}, which will work similarly to the
{{node-locality-delay}}, and will therefore bypass the locality wait factor.
This way we will attempt assigning off-switch containers after
{{rack-locality-delay}} missed opportunities.
Thoughts?
[~arun.sur...@gmail.com]
was (Author: kkaranasos):
The described issue was observed together with [~asuresh] and [~curino], while
examining some of our internal applications that request containers in small
batches.
We also brought it to the attention of [~jlowe].
One way to solve the problem is to introduce an additional parameter, namely
{{rack-locality-delay}}, which will work similarly to the
{{node-locality-delay}}, and will therefore bypass the locality wait factor.
This way we will attempt assigning off-switch containers after
{{rack-locality-delay}} missed opportunities.
Thoughts?
> 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
>
> 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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