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From "Kay Ousterhout (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (SPARK-18967) Locality preferences should be used when scheduling even when delay scheduling is turned off
Date Tue, 07 Feb 2017 06:39:41 GMT

     [ https://issues.apache.org/jira/browse/SPARK-18967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kay Ousterhout resolved SPARK-18967.
------------------------------------
       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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