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https://issues.apache.org/jira/browse/HIVE-2340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13566902#comment-13566902
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Gunther Hagleitner commented on HIVE-2340:
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Partial review on phabricator. Biggest question is around 
"hive.optimize.reducededuplication.min.reducer". That basically disables the 
"orderby followed by groupby" optimization which was the original motivation 
for the jira. Navis, can you explain this some more?

Might be another ticket, but would it be possible to optimize group by/sort by 
as well with this?
                
> optimize orderby followed by a groupby
> --------------------------------------
>
>                 Key: HIVE-2340
>                 URL: https://issues.apache.org/jira/browse/HIVE-2340
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Query Processor
>            Reporter: Navis
>            Assignee: Navis
>            Priority: Minor
>              Labels: perfomance
>         Attachments: ASF.LICENSE.NOT.GRANTED--HIVE-2340.D1209.1.patch, 
> ASF.LICENSE.NOT.GRANTED--HIVE-2340.D1209.2.patch, 
> ASF.LICENSE.NOT.GRANTED--HIVE-2340.D1209.3.patch, 
> ASF.LICENSE.NOT.GRANTED--HIVE-2340.D1209.4.patch, 
> ASF.LICENSE.NOT.GRANTED--HIVE-2340.D1209.5.patch, HIVE-2340.1.patch.txt, 
> HIVE-2340.D1209.6.patch, HIVE-2340.D1209.7.patch, HIVE-2340.D1209.8.patch, 
> HIVE-2340.D1209.9.patch, testclidriver.txt
>
>
> Before implementing optimizer for JOIN-GBY, try to implement RS-GBY 
> optimizer(cluster-by following group-by).

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