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https://issues.apache.org/jira/browse/HIVE-20370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16577838#comment-16577838
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Gopal V commented on HIVE-20370:
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Zero rows on the outer side is often found within MERGE statements with the
dynamic semi-join enabled (i.e all rows are new primary keys and there's no
rows to update).
> Vectorization: Add Native Vector MapJoin hash table optimization for
> Left/Right Outer Joins when there are no Small Table values
> --------------------------------------------------------------------------------------------------------------------------------
>
> Key: HIVE-20370
> URL: https://issues.apache.org/jira/browse/HIVE-20370
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Reporter: Matt McCline
> Assignee: Matt McCline
> Priority: Critical
> Attachments: HIVE-20370.01.patch
>
>
> Similar to Native Vector MapJoin's InnerBigOnly optimization that uses an
> efficient Hash Multi-Set with a counter instead of a Hash Map with an empty
> value, do the same for Outer joins.
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