[jira] [Updated] (HIVE-2621) Allow multiple group bys with the same input data and spray keys to be run on the same reducer.

["He Yongqiang (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-2621?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

He Yongqiang updated HIVE-2621:
-------------------------------

    Resolution: Fixed
        Status: Resolved  (was: Patch Available)

committed, thanks Kevin!
                
> Allow multiple group bys with the same input data and spray keys to be run on the same reducer.
> -----------------------------------------------------------------------------------------------
>
>                 Key: HIVE-2621
>                 URL: https://issues.apache.org/jira/browse/HIVE-2621
>             Project: Hive
>          Issue Type: New Feature
>            Reporter: Kevin Wilfong
>            Assignee: Kevin Wilfong
>         Attachments: HIVE-2621.1.patch.txt, HIVE-2621.D567.1.patch, HIVE-2621.D567.2.patch, HIVE-2621.D567.3.patch, HIVE-2621.D567.4.patch
>
>
> Currently, when a user runs a query, such as a multi-insert, where each insertion subclause consists of a simple query followed by a group by, the group bys for each clause are run on a separate reducer.  This requires writing the data for each group by clause to an intermediate file, and then reading it back.  This uses a significant amount of the total CPU consumed by the query for an otherwise simple query.
> If the subclauses are grouped by their distinct expressions and group by keys, with all of the group by expressions for a group of subclauses run on a single reducer, this would reduce the amount of reading/writing to intermediate files for some queries.
> To do this, for each group of subclauses, in the mapper we would execute a the filters for each subclause 'or'd together (provided each subclause has a filter) followed by a reduce sink.  In the reducer, the child operators would be each subclauses filter followed by the group by and any subsequent operations.
> Note that this would require turning off map aggregation, so we would need to make using this type of plan configurable.

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