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https://issues.apache.org/jira/browse/HIVE-3086?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13457891#comment-13457891
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Nadeem Moidu commented on HIVE-3086:
------------------------------------

@Yin Huai: The join operator for skewed keys is automatically converted to map 
join when the map join optimization is performed. That is not included in this 
patch.
                
> Skewed Join Optimization
> ------------------------
>
>                 Key: HIVE-3086
>                 URL: https://issues.apache.org/jira/browse/HIVE-3086
>             Project: Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Nadeem Moidu
>            Assignee: Namit Jain
>             Fix For: 0.10.0
>
>         Attachments: hive.3086.1.patch, hive.3086.2.patch, hive.3086.3.patch, 
> hive.3086.4.patch, hive.3086.5.patch, hive.3086.6.patch
>
>
> During a join operation, if one of the columns has a skewed key, it can cause 
> that particular reducer to become the bottleneck. The following feature will 
> address it:
> https://cwiki.apache.org/confluence/display/Hive/Skewed+Join+Optimization

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