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https://issues.apache.org/jira/browse/SPARK-2294?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045433#comment-14045433
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Mridul Muralidharan commented on SPARK-2294:
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I agree; We should bump no locality pref and speculative tasks to NODE_LOCAL
level after NODE_LOCAL tasks have been scheduled (if available), and not check
for them at PROCESS_LOCAL max locality. So they get scheduled before RACK_LOCAL
but after NODE_LOCAL.
This is an artifact of the design when there was no PROCESS_LOCAL and
NODE_LOCAL was the best schedule possible (without explicitly having these
level : we had node and any).
> TaskSchedulerImpl and TaskSetManager do not properly prioritize which tasks
> get assigned to an executor
> -------------------------------------------------------------------------------------------------------
>
> Key: SPARK-2294
> URL: https://issues.apache.org/jira/browse/SPARK-2294
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 1.0.0, 1.0.1
> Reporter: Kay Ousterhout
>
> If an executor E is free, a task may be speculatively assigned to E when
> there are other tasks in the job that have not been launched (at all) yet.
> Similarly, a task without any locality preferences may be assigned to E when
> there was another NODE_LOCAL task that could have been scheduled.
> This happens because TaskSchedulerImpl calls TaskSetManager.resourceOffer
> (which in turn calls TaskSetManager.findTask) with increasing locality
> levels, beginning with PROCESS_LOCAL, followed by NODE_LOCAL, and so on until
> the highest currently allowed level. Now, supposed NODE_LOCAL is the highest
> currently allowed locality level. The first time findTask is called, it will
> be called with max level PROCESS_LOCAL; if it cannot find any PROCESS_LOCAL
> tasks, it will try to schedule tasks with no locality preferences or
> speculative tasks. As a result, speculative tasks or tasks with no
> preferences may be scheduled instead of NODE_LOCAL tasks.
> cc [~matei]
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