[jira] [Commented] (HIVE-3562) Some limit can be pushed down to map stage

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

    [ https://issues.apache.org/jira/browse/HIVE-3562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13511402#comment-13511402 ] 

Namit Jain commented on HIVE-3562:
----------------------------------

I think it would be simple to keep it a hive only change.
I agree that Hadoop change is more general, but it may be painful/time-consuming to backport.
In most of the cases, k would be small, and it makes perfect sense to put a limit on k, as you suggested above.

What do you think ?
Should we go with the hive-only change ?
                
> 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
>
>
> 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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