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https://issues.apache.org/jira/browse/SPARK-18890?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15753833#comment-15753833
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Guoqiang Li commented on SPARK-18890:
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[~kayousterhout]
I ran a test having 10 million tasks, and did not see the bottleneck. Can you
provide any cases where CGSB becomes a bottleneck?
On the use of broadcast transmission tasks, broadcaset size is proportional to
the number of tasks(The location and partition of each task are different). If
the size of each serialized location is 100 bytes, then 10 million tasks
generated a broadcaset with 953M size
> Do all task serialization in CoarseGrainedExecutorBackend thread (rather than
> TaskSchedulerImpl)
> ------------------------------------------------------------------------------------------------
>
> Key: SPARK-18890
> URL: https://issues.apache.org/jira/browse/SPARK-18890
> Project: Spark
> Issue Type: Bug
> Components: Scheduler
> Affects Versions: 2.1.0
> Reporter: Kay Ousterhout
> Priority: Minor
>
> As part of benchmarking this change:
> https://github.com/apache/spark/pull/15505 and alternatives, [~shivaram] and
> I found that moving task serialization from TaskSetManager (which happens as
> part of the TaskSchedulerImpl's thread) to CoarseGranedSchedulerBackend leads
> to approximately a 10% reduction in job runtime for a job that counted 10,000
> partitions (that each had 1 int) using 20 machines. Similar performance
> improvements were reported in the pull request linked above. This would
> appear to be because the TaskSchedulerImpl thread is the bottleneck, so
> moving serialization to CGSB reduces runtime. This change may *not* improve
> runtime (and could potentially worsen runtime) in scenarios where the CGSB
> thread is the bottleneck (e.g., if tasks are very large, so calling launch to
> send the tasks to the executor blocks on the network).
> One benefit of implementing this change is that it makes it easier to
> parallelize the serialization of tasks (different tasks could be serialized
> by different threads). Another benefit is that all of the serialization
> occurs in the same place (currently, the Task is serialized in
> TaskSetManager, and the TaskDescription is serialized in CGSB).
> I'm not totally convinced we should fix this because it seems like there are
> better ways of reducing the serialization time (e.g., by re-using a single
> serialized object with the Task/jars/files and broadcasting it for each
> stage) but I wanted to open this JIRA to document the discussion.
> cc [~witgo]
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