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https://issues.apache.org/jira/browse/SPARK-8964?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Davies Liu resolved SPARK-8964.
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Resolution: Fixed
Fix Version/s: 2.0.0
Issue resolved by pull request 7334
[https://github.com/apache/spark/pull/7334]
> Use Exchange in limit operations (per partition limit -> exchange to one
> partition -> per partition limit)
> ----------------------------------------------------------------------------------------------------------
>
> Key: SPARK-8964
> URL: https://issues.apache.org/jira/browse/SPARK-8964
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Reporter: Josh Rosen
> Fix For: 2.0.0
>
>
> Spark SQL's physical Limit operator currently performs its own shuffle rather
> than using Exchange to perform the shuffling. This is less efficient since
> this non-exchange shuffle path won't be able to benefit from SQL-specific
> shuffling optimizations, such as SQLSerializer2. It also involves additional
> unnecessary row copying.
> Instead, I think that we should rewrite Limit to expand into three physical
> operators:
> PerParititonLimit -> Exchange to one partition -> PerPartitionLimit
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