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https://issues.apache.org/jira/browse/SPARK-18967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kay Ousterhout resolved SPARK-18967.
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Resolution: Fixed
Fix Version/s: 2.2
> Locality preferences should be used when scheduling even when delay
> scheduling is turned off
> --------------------------------------------------------------------------------------------
>
> Key: SPARK-18967
> URL: https://issues.apache.org/jira/browse/SPARK-18967
> Project: Spark
> Issue Type: Bug
> Components: Scheduler
> Affects Versions: 2.1.0
> Reporter: Imran Rashid
> Assignee: Imran Rashid
> Fix For: 2.2
>
>
> If you turn delay scheduling off by setting {{spark.locality.wait=0}}, you
> effectively turn off the use the of locality preferences when there is a bulk
> scheduling event. {{TaskSchedulerImpl}} will use resources based on whatever
> random order it decides to shuffle them, rather than taking advantage of the
> most local options.
> This happens because {{TaskSchedulerImpl}} offers resources to a
> {{TaskSetManager}} one at a time, each time subject to a maxLocality
> constraint. However, that constraint doesn't move through all possible
> locality levels -- it uses [{{tsm.myLocalityLevels}}
> |https://github.com/apache/spark/blob/1a64388973711b4e567f25fa33d752066a018b49/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala#L360].
> And {{tsm.myLocalityLevels}} [skips locality levels completely if the wait
> == 0 |
> https://github.com/apache/spark/blob/1a64388973711b4e567f25fa33d752066a018b49/core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala#L953].
> So with delay scheduling off, {{TaskSchedulerImpl}} immediately jumps to
> giving tsms the offers with {{maxLocality = ANY}}.
> *WORKAROUND*: instead of setting {{spark.locality.wait=0}}, use
> {{spark.locality.wait=1ms}}. The one downside of this is if you have tasks
> that actually take less than 1ms. You could even run into SPARK-18886. But
> that is a relatively unlikely scenario for real workloads.
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