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Posted to issues@spark.apache.org by "Reynold Xin (JIRA)" <ji...@apache.org> on 2017/02/07 09:14:41 UTC
[jira] [Updated] (SPARK-18967) Locality preferences should be used
when scheduling even when delay scheduling is turned off
[ https://issues.apache.org/jira/browse/SPARK-18967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Reynold Xin updated SPARK-18967:
--------------------------------
Fix Version/s: (was: 2.2)
2.2.0
> 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: 2.2.0
>
>
> 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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