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From "Jesus Camacho Rodriguez (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-13982) Extension to limit push down through order by & group by
Date Thu, 09 Jun 2016 18:29:21 GMT
Jesus Camacho Rodriguez created HIVE-13982:
----------------------------------------------

             Summary: Extension to limit push down through order by & group by
                 Key: HIVE-13982
                 URL: https://issues.apache.org/jira/browse/HIVE-13982
             Project: Hive
          Issue Type: Improvement
          Components: Physical Optimizer
    Affects Versions: 2.2.0
            Reporter: Jesus Camacho Rodriguez
            Assignee: Jesus Camacho Rodriguez
         Attachments: HIVE-13982.patch

Queries which follow the format are not optimal with map-side aggregation, because the Map
1 does not have TopN in the reduce sink.

These queries shuffle 100% of the aggregate in cases where the reduce de-dup does not kick
in. 

As input data grows, it falls off a cliff of performance after 4 reducers.

{code}
select state, city, sum(sales) from table
group by state, city
order by state, city
limit 10;
{code}

{code}
select state, city, sum(sales) from table
group by city, state
order by state, city
limit 10;
{code}

{code}
select state, city, sum(sales) from table
group by city, state
order by state desc, city
limit 10;
{code}



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