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Date: Wed, 19 Sep 2012 05:02:08 +1100 (NCT)
From: "Namit Jain (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
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Subject: [jira] [Commented] (HIVE-3086) Skewed Join Optimization
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    [ https://issues.apache.org/jira/browse/HIVE-3086?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13458005#comment-13458005 ] 

Namit Jain commented on HIVE-3086:
----------------------------------

[~yhuai], right now both the input and output tables will be scanned twice.
                
> 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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