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https://issues.apache.org/jira/browse/SPARK-37652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17459911#comment-17459911
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Apache Spark commented on SPARK-37652:
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User 'mcdull-zhang' has created a pull request for this issue:
https://github.com/apache/spark/pull/34908
> Support optimize skewed join through union
> ------------------------------------------
>
> Key: SPARK-37652
> URL: https://issues.apache.org/jira/browse/SPARK-37652
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: mcdull_zhang
> Priority: Minor
>
> `OptimizeSkewedJoin` rule will take effect only when the plan has two
> ShuffleQueryStageExec。
> With `Union`, it might break the assumption. For example, the following plans
> *scenes 1*
> {noformat}
> Union
> SMJ
> ShuffleQueryStage
> ShuffleQueryStage
> SMJ
> ShuffleQueryStage
> ShuffleQueryStage
> {noformat}
> *scenes 2*
> {noformat}
> Union
> SMJ
> ShuffleQueryStage
> ShuffleQueryStage
> HashAggregate
> {noformat}
> when one or more of the SMJ data in the above plan is skewed, it cannot be
> processed at present.
> It's better to support partial optimize with Union.
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