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https://issues.apache.org/jira/browse/HIVE-9392?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14529623#comment-14529623
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Pengcheng Xiong commented on HIVE-9392:
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[~mmokhtar], could you please take a look? Thanks.
> JoinStatsRule miscalculates join cardinality as incorrect NDV is used due to
> column names having duplicated fqColumnName
> ------------------------------------------------------------------------------------------------------------------------
>
> Key: HIVE-9392
> URL: https://issues.apache.org/jira/browse/HIVE-9392
> Project: Hive
> Issue Type: Bug
> Components: Physical Optimizer
> Affects Versions: 0.14.0
> Reporter: Mostafa Mokhtar
> Assignee: Prasanth Jayachandran
> Priority: Critical
> Attachments: HIVE-9392.01.patch, HIVE-9392.1.patch, HIVE-9392.2.patch
>
>
> In JoinStatsRule.process the join column statistics are stored in HashMap
> joinedColStats, the key used which is the ColStatistics.fqColName is
> duplicated between join column in the same vertex, as a result distinctVals
> ends up having duplicated values which negatively affects the join
> cardinality estimation.
> The duplicate keys are usually named KEY.reducesinkkey0.
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