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Posted to dev@hive.apache.org by "Jason Dere (JIRA)" <ji...@apache.org> on 2017/03/25 01:29:41 UTC

[jira] [Created] (HIVE-16298) Add config to specify multi-column joins have correlated columns

Jason Dere created HIVE-16298:
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             Summary: 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


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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