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https://issues.apache.org/jira/browse/HIVE-15234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15690721#comment-15690721
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Jesus Camacho Rodriguez commented on HIVE-15234:
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[~ashutoshc], patch looks good in general.
I have only one question. Why don't we use HiveSemiJoin in all cases? I think
we are always generating HiveSemiJoin instances in any case if we are using the
right builders (or we probably should).
> Semijoin cardinality estimation can be improved
> -----------------------------------------------
>
> Key: HIVE-15234
> URL: https://issues.apache.org/jira/browse/HIVE-15234
> Project: Hive
> Issue Type: Bug
> Components: CBO, Logical Optimizer
> Affects Versions: 2.0.0, 2.1.0
> Reporter: Ashutosh Chauhan
> Assignee: Ashutosh Chauhan
> Attachments: HIVE-15234.1.patch, HIVE-15234.2.patch, HIVE-15234.patch
>
>
> Currently calcite optimization rules rely on (Hive)SemiJoin to represent semi
> join node, whereas Stats estimate use {{leftSemiJoin}} field of Join to
> estimate stats. As a result semi-join specific stats calculation logic is
> never hit since at plan generation time HiveSemiJoin is created and
> leftSemiJoin field of Join is never set.
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