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Posted to issues@hive.apache.org by "Jason Dere (JIRA)" <ji...@apache.org> on 2017/09/21 18:12:00 UTC

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

     [ https://issues.apache.org/jira/browse/HIVE-16298?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Dere updated HIVE-16298:
------------------------------
    Fix Version/s:     (was: 2.3.0)
                   3.0.0

> 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: 3.0.0
>
>         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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