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From "Yin Huai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3562) Some limit can be pushed down to map stage
Date Fri, 23 Aug 2013 16:31:51 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13748683#comment-13748683
] 

Yin Huai commented on HIVE-3562:
--------------------------------

Implementing RSHash as an operator sounds good. We can also use it in front of the RS of the
right table of left semi join. Right now, there is a GBY. It is not straightforward in the
query plan.
                
> Some limit can be pushed down to map stage
> ------------------------------------------
>
>                 Key: HIVE-3562
>                 URL: https://issues.apache.org/jira/browse/HIVE-3562
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Navis
>            Assignee: Navis
>            Priority: Trivial
>         Attachments: HIVE-3562.D5967.1.patch, HIVE-3562.D5967.2.patch, HIVE-3562.D5967.3.patch,
HIVE-3562.D5967.4.patch, HIVE-3562.D5967.5.patch, HIVE-3562.D5967.6.patch
>
>
> Queries with limit clause (with reasonable number), for example
> {noformat}
> select * from src order by key limit 10;
> {noformat}
> makes operator tree, 
> TS-SEL-RS-EXT-LIMIT-FS
> But LIMIT can be partially calculated in RS, reducing size of shuffling.
> TS-SEL-RS(TOP-N)-EXT-LIMIT-FS

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