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https://issues.apache.org/jira/browse/HIVE-18819?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16379900#comment-16379900
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Matt McCline commented on HIVE-18819:
-------------------------------------
Also, it looks like they way we custom instantiate the
IfExprColumn{Null|CondExpr}, IfExprCondExprCondExpr,
IfExprCondExpr{Null|Column} we don't reuse the scratch columns... You can see
this by the higher column numbers in the EXPLAIN VECTORIZATION DETAIL display.
> Vectorization: Optimize IF statement expression evaluation of THEN/ELSE
> -----------------------------------------------------------------------
>
> Key: HIVE-18819
> URL: https://issues.apache.org/jira/browse/HIVE-18819
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Affects Versions: 3.0.0
> Reporter: Matt McCline
> Assignee: Matt McCline
> Priority: Critical
> Attachments: HIVE-18819.01.patch
>
>
> Currently, all the rows of a batch are evaluated for the THEN and ELSE
> expressions even though only a value from one of them is needed for any
> particular row.
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