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https://issues.apache.org/jira/browse/HIVE-16298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15941475#comment-15941475
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Prasanth Jayachandran commented on HIVE-16298:
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lgtm, +1
> Add config to specify multi-column joins have correlated columns
> ----------------------------------------------------------------
>
> Key: HIVE-16298
> URL: https://issues.apache.org/jira/browse/HIVE-16298
> Project: Hive
> Issue Type: Bug
> Reporter: Jason Dere
> Assignee: Jason Dere
> Attachments: HIVE-16298.1.patch
>
>
> The default row estimation for multi-key joins divides the row estimate by
> the product of the NDVs for each join column, which can cause the row
> estimate to be low. Try adding a config to assume the columns are correlated,
> where we only divide the row estimate by the largest NDV.
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