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https://issues.apache.org/jira/browse/HIVE-9392?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mostafa Mokhtar updated HIVE-9392:
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Summary: JoinStatsRule miscalculates join cardinality as incorrect NDV is
used due to column names having duplicated fqColumnName (was: Hive :
JoinStatsRule overwrites the column statistics in HashMap because column names
have duplicate fqColumnName)
> 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
> Fix For: 0.15.0
>
>
> 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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