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https://issues.apache.org/jira/browse/SPARK-27070?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen reassigned SPARK-27070:
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Assignee: Yuli Fiterman
> DefaultPartitionCoalescer can lock up driver for hours
> ------------------------------------------------------
>
> Key: SPARK-27070
> URL: https://issues.apache.org/jira/browse/SPARK-27070
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.3.1, 2.3.2, 2.4.0
> Reporter: Yuli Fiterman
> Assignee: Yuli Fiterman
> Priority: Major
>
> We're running Spark on EMR reading large datasets from S3. When trying to
> coalesce a UnionRDD of two large FileScanRDDs (each with a few million
> partitions) into around 8k partitions the driver can stall for over an hour.
>
> Profiler shows that over 90% of the time is spent in TimSort which is invoked
> by `pickBin`. This seems like a very inefficient way to find the least
> occupied PartitionGroup. IMO a better way would just using the `min` method
> on the ArrayBuffer of `PartitionGroup`s
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