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https://issues.apache.org/jira/browse/SPARK-22683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16289101#comment-16289101
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Julien Cuquemelle commented on SPARK-22683:
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Hi [~srowen],
Just a small remark about the use of schedulerBacklogTimeout to slow down the
build up of executors:
We have recently experienced an issue where the executors allocation by Yarn
was slow; this resulted in the first executors having done a lot of tasks
(hence storing a lot of blocks), and become a contention point in the
subsequent stage, when all executors have finally been allocated and try to
access the first exe's blocks remotely.
So I guess the fact that the schedulerBacklogTimeout is very short and allows
to quicky ramp up the number of executors is not trivial to alter if we don't
want to create a too big imbalance in blocks stored by executors.
So I don't think that using this parameter to alter resource usage by the
dynamic allocation is a good choice, for this very reason and also because of
the fact that it is highly dependant on the wall clock time of the job.
> DynamicAllocation wastes resources by allocating containers that will barely
> be used
> ------------------------------------------------------------------------------------
>
> Key: SPARK-22683
> URL: https://issues.apache.org/jira/browse/SPARK-22683
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.1.0, 2.2.0
> Reporter: Julien Cuquemelle
> Labels: pull-request-available
>
> let's say an executor has spark.executor.cores / spark.task.cpus taskSlots
> The current dynamic allocation policy allocates enough executors
> to have each taskSlot execute a single task, which minimizes latency,
> but wastes resources when tasks are small regarding executor allocation
> and idling overhead.
> By adding the tasksPerExecutorSlot, it is made possible to specify how many
> tasks
> a single slot should ideally execute to mitigate the overhead of executor
> allocation.
> PR: https://github.com/apache/spark/pull/19881
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