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https://issues.apache.org/jira/browse/HIVE-15227?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15672817#comment-15672817
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Ashutosh Chauhan commented on HIVE-15227:
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yes.. there is. You may note (from the plan in attached patch) that Gby is only
in mapper, not in reducer. This is possible since LSJ operator understands the
semantics, such that GBy in reducer is obviated. Net perf win here is to not
compute GBy on reducer side.
> Optimize join + gby into semijoin
> ---------------------------------
>
> Key: HIVE-15227
> URL: https://issues.apache.org/jira/browse/HIVE-15227
> Project: Hive
> Issue Type: Bug
> Components: Logical Optimizer
> Reporter: Ashutosh Chauhan
> Assignee: Ashutosh Chauhan
> Attachments: HIVE-15227.patch
>
>
> Calcite has a rule which can do this transformation. Lets take advantage of
> this since Hive has native Left semi join operator.
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