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https://issues.apache.org/jira/browse/SPARK-30417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17007694#comment-17007694
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Thomas Graves commented on SPARK-30417:
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[~yuchen.huo] is this something you could work on?
> SPARK-29976 calculation of slots wrong for Standalone Mode
> ----------------------------------------------------------
>
> Key: SPARK-30417
> URL: https://issues.apache.org/jira/browse/SPARK-30417
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 3.0.0
> Reporter: Thomas Graves
> Priority: Major
>
> In SPARK-29976 we added a config to determine if we should allow speculation
> when the number of tasks is less then the number of slots on a single
> executor. The problem is that for standalone mode (and mesos coarse
> grained) the EXECUTOR_CORES config is not set properly by default. In those
> modes the number of executor cores is all the cores of the Worker. The
> default of EXECUTOR_CORES is 1.
> The calculation:
> {color:#000080}val {color}{color:#660e7a}speculationTasksLessEqToSlots
> {color}= {color:#660e7a}numTasks {color}<=
> ({color:#660e7a}conf{color}.get({color:#660e7a}EXECUTOR_CORES{color}) /
> sched.{color:#660e7a}CPUS_PER_TASK{color})
> If someone set the cpus per task > 1 then this would end up being false even
> if 1 task. Note that the default case where cpus per task is 1 and executor
> cores is 1 it works out ok but is only applied if 1 task vs number of slots
> on the executor.
> Here we really don't know the number of executor cores for standalone mode or
> mesos so I think a decent solution is to just use 1 in those cases and
> document the difference.
> Something like
> max({color:#660e7a}conf{color}.get({color:#660e7a}EXECUTOR_CORES{color}) /
> sched.{color:#660e7a}CPUS_PER_TASK{color}, 1)
>
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