[jira] Updated: (HADOOP-4139) [Hive] multi group by statement is not optimized

["Namit Jain (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-4139?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Namit Jain updated HADOOP-4139:
-------------------------------

    Component/s: contrib/hive

> [Hive] multi group by statement is not optimized
> ------------------------------------------------
>
>                 Key: HADOOP-4139
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4139
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: contrib/hive
>            Reporter: Namit Jain
>            Assignee: Namit Jain
>         Attachments: patch1
>
>
> A simple multi-group by statement is not optimized. A simple statement like:
> FROM SRC
> INSERT OVERWRITE TABLE DEST1 SELECT SRC.key, count(distinct  SUBSTR(SRC.value,4)) GROUP BY SRC.key
> INSERT OVERWRITE TABLE DEST2 SELECT SRC.key, count(distinct  SUBSTR(SRC.value,4)) GROUP BY SRC.key;
> results in making 2 copies of the data (SRC). Instead, the data can be first partially aggregated on the distinct value and then aggregated. 
> The first step can be common to all group bys.

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