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https://issues.apache.org/jira/browse/HIVE-23723?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17142863#comment-17142863
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Attila Magyar edited comment on HIVE-23723 at 6/23/20, 5:14 PM:
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[~jcamachorodriguez],
??Concerning your patch, it seems you are removing the original limit on top of
the left outer join? Note that you cannot remove it : If you have 5 input rows
on the left side, you know the LOJ will produce at least 5 rows, however you
cannot guarantee the join will produce 5 rows at most.??
Got it, that should be kept indeed. However reason why additional reducers are
introduced by the limittranspose implementation is not fully clear to me.
Do you think we should drop this patch as it's already implemented by the
limittranspose, and focus on tweaking the existing implementation?
cc: [~ashutoshc]
was (Author: amagyar):
[~jcamachorodriguez],
??Concerning your patch, it seems you are removing the original limit on top of
the left outer join? Note that you cannot remove it : If you have 5 input rows
on the left side, you know the LOJ will produce at least 5 rows, however you
cannot guarantee the join will produce 5 rows at most.??
Got it, that should be kept indeed. However reason why additional reducers are
introduced by the limittranspose implementation is not fully clear to me.
Do you think we should drop this patch as it's already implemented by the
limittranspose, and focus on tweaking the existing implementation?
> Limit operator pushdown through LOJ
> -----------------------------------
>
> Key: HIVE-23723
> URL: https://issues.apache.org/jira/browse/HIVE-23723
> Project: Hive
> Issue Type: Improvement
> Components: Hive
> Reporter: Attila Magyar
> Assignee: Attila Magyar
> Priority: Major
> Fix For: 4.0.0
>
> Attachments: HIVE-23723.1.patch
>
>
> Limit operator (without an order by) can be pushed through SELECTS and LEFT
> OUTER JOINs.
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