GitHub user AjithShetty2489 opened a pull request:

    https://github.com/apache/spark/pull/20770

    [SPARK-23626][CORE] DAGScheduler blocked due to JobSubmitted event

    ## What changes were proposed in this pull request?
    
    DAGScheduler becomes a bottleneck in cluster when multiple JobSubmitted 
events has to be processed as DAGSchedulerEventProcessLoop is single threaded 
and it will block other tasks in queue like TaskCompletion.
    The JobSubmitted event is time consuming depending on the nature of the job 
(Example: calculating parent stage dependencies, shuffle dependencies, 
partitions) and thus it blocks all the events to be processed.
    
    Similarly in my cluster some jobs partition calculation is time consuming 
(Similar to stack at SPARK-2647) hence it slows down the spark 
DAGSchedulerEventProcessLoop which results in user jobs to slowdown, even if 
its tasks are finished within seconds, as TaskCompletion Events are processed 
at a slower rate due to blockage.
    
    Move the ResultStage creation to call site thread, which will avoid 
blocking of DAGScheduler thread for other events
    
    Refer: 
http://apache-spark-developers-list.1001551.n3.nabble.com/Spark-Scheduler-Spark-DAGScheduler-scheduling-performance-hindered-on-JobSubmitted-Event-td23562.html
    
    ## How was this patch tested?
    
    Manual test to verify blockage before and after applying patch.


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/AjithShetty2489/spark sparkDag

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/spark/pull/20770.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #20770
    
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commit 34cc4dc035f7262678b6561700511e81fe8a368a
Author: Ajith <ajith2489@...>
Date:   2018-03-07T13:37:50Z

    DAGScheduler blocked due to JobSubmitted event

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