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https://issues.apache.org/jira/browse/SPARK-22408?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Patrick Woody updated SPARK-22408:
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Summary: RelationalGroupedDataset's distinct pivot value calculation
launches unnecessary stages (was: RelationalGroupedDataset's distinct pivot
value calculation can launch many stages)
> RelationalGroupedDataset's distinct pivot value calculation launches
> unnecessary stages
> ---------------------------------------------------------------------------------------
>
> Key: SPARK-22408
> URL: https://issues.apache.org/jira/browse/SPARK-22408
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.2.0
> Reporter: Patrick Woody
>
> When calculating the distinct values for a pivot in RelationalGroupedDataset
> (https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala#L322),
> we sort before doing a take(maxValues + 1).
> We should be able to improve this by adding a global limit before the sort,
> which should reduce the work of the sort, and by simply doing a collect to
> avoid multiple launching multiple stages as a part of the take.
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