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Posted to issues@spark.apache.org by "Cheng Su (Jira)" <ji...@apache.org> on 2020/08/18 06:15:00 UTC
[jira] [Commented] (SPARK-32649) Optimize BHJ/SHJ inner and semi
join with empty hashed relation
[ https://issues.apache.org/jira/browse/SPARK-32649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17179385#comment-17179385 ]
Cheng Su commented on SPARK-32649:
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[~cloud_fan] - sorry for ping as this is not major improvement. Could you let me know if this is worth adding in upstream? The code change is pretty minor. If yes, I can work on a PR for it. cc [~leanken] as well FYI thanks.
> Optimize BHJ/SHJ inner and semi join with empty hashed relation
> ---------------------------------------------------------------
>
> Key: SPARK-32649
> URL: https://issues.apache.org/jira/browse/SPARK-32649
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 3.1.0
> Reporter: Cheng Su
> Priority: Trivial
>
> With `EmptyHashedRelation` introduced in [https://github.com/apache/spark/pull/29389], it inspired me that there's a minor optimization we can apply to broadcast hash join and shuffled hash join if build side hashed relation is empty.
> If build side hashed relation is empty (i.e. build side is empty)
> 1.inner join: we don't need to execute stream side at all, just return an empty iterator - [https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/joins/HashJoin.scala#L152]
> 2.semi join: we don't need to execute stream side at all, just return an empty iterator - [https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/joins/HashJoin.scala#L227] .
> This is not common that build side is empty, but in case it is, we can leverage it to not execute stream side at all for better query CPU/IO performance.
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