[jira] [Work started] (HIVE-13982) Extension to limit push down through order by & group by

["Jesus Camacho Rodriguez (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-13982?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on HIVE-13982 started by Jesus Camacho Rodriguez.
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> 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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