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https://issues.apache.org/jira/browse/SPARK-23626?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16390825#comment-16390825
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Apache Spark commented on SPARK-23626:
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User 'AjithShetty2489' has created a pull request for this issue:
https://github.com/apache/spark/pull/20770

> Spark DAGScheduler scheduling performance hindered on JobSubmitted Event
> ------------------------------------------------------------------------
>
>                 Key: SPARK-23626
>                 URL: https://issues.apache.org/jira/browse/SPARK-23626
>             Project: Spark
>          Issue Type: Bug
>          Components: Scheduler
>    Affects Versions: 2.2.1
>            Reporter: Ajith S
>            Priority: Major
>
> 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.
>  
> I see multiple JIRA referring to this behavior
> https://issues.apache.org/jira/browse/SPARK-2647
> https://issues.apache.org/jira/browse/SPARK-4961
>  
> 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.



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