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From "Jesus Camacho Rodriguez (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-17043) Remove non unique columns from group by keys if not referenced later
Date Sat, 06 Oct 2018 22:43:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-17043?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16640892#comment-16640892
] 

Jesus Camacho Rodriguez commented on HIVE-17043:
------------------------------------------------

[~vgarg], I left three minor comments in RB, could you take a look? I think other than that,
patch LGTM.

> Remove non unique columns from group by keys if not referenced later
> --------------------------------------------------------------------
>
>                 Key: HIVE-17043
>                 URL: https://issues.apache.org/jira/browse/HIVE-17043
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Logical Optimizer
>    Affects Versions: 3.0.0
>            Reporter: Ashutosh Chauhan
>            Assignee: Vineet Garg
>            Priority: Major
>         Attachments: HIVE-17043.1.patch, HIVE-17043.10.patch, HIVE-17043.11.patch, HIVE-17043.2.patch,
HIVE-17043.3.patch, HIVE-17043.4.patch, HIVE-17043.5.patch, HIVE-17043.6.patch, HIVE-17043.7.patch,
HIVE-17043.8.patch, HIVE-17043.9.patch
>
>
> Group by keys may be a mix of unique (or primary) keys and regular columns. In such cases
presence of regular column won't alter cardinality of groups. So, if regular columns are not
referenced later, they can be dropped from group by keys. Depending on operator tree may result
in those columns not being read at all from disk in best case. In worst case, we will avoid
shuffling and sorting regular columns from mapper to reducer, which still could be substantial
CPU and network savings.



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