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https://issues.apache.org/jira/browse/HIVE-16298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15942194#comment-15942194
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Lefty Leverenz commented on HIVE-16298:
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[~jdere], since this was committed to master after branch-2 split off on March
23 (11:06pm PDT) the fix version should say 3.0.0. If you want it in 2.3.0
commit it to branch-2. For 2.2.0 commit to branch-2.2.
> 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: Siddharth Seth
> Labels: TODOC3.0
> Fix For: 2.2.0
>
> Attachments: HIVE-16298.1.patch, HIVE-16298.2.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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