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https://issues.apache.org/jira/browse/DRILL-6755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16626641#comment-16626641
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Boaz Ben-Zvi commented on DRILL-6755:
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More precisely, when the probe side does not even return a schema, just NONE.
When the probe side does first return a schema (i.e. OK_NEW_SCHEMA), then the
Hash Tables are built, as the code does not "sniff" further into the probe side
to check if actual data is coming.
> HashJoin should not build hash tables when probe side is empty.
> ---------------------------------------------------------------
>
> Key: DRILL-6755
> URL: https://issues.apache.org/jira/browse/DRILL-6755
> Project: Apache Drill
> Issue Type: Improvement
> Reporter: Timothy Farkas
> Assignee: Boaz Ben-Zvi
> Priority: Major
>
> Currently when doing an Inner or a Right join we still build hashtables when
> the probe side is empty. A performance optimization would be to not build
> them.
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