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From "Navis (JIRA)" <>
Subject [jira] [Commented] (HIVE-3972) Support using multiple reducer for fetching order by results
Date Mon, 30 Sep 2013 06:48:27 GMT


Navis commented on HIVE-3972:

[~ashutoshc] A little. It can be an alternative way to acquire ordered result without sampling.
If this would be included, simple select queries can use this by default, because it's simpler
than HIVE-3562 and number of reducer also can be calculated automatically in a same way with
normal MR. HIVE-3562 would be still useful for making final output files in totally-ordered

HIVE-3972 is HIVE-4002 for order-by.

> Support using multiple reducer for fetching order by results
> ------------------------------------------------------------
>                 Key: HIVE-3972
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Navis
>            Assignee: Navis
>            Priority: Minor
>         Attachments: HIVE-3972.D8349.1.patch, HIVE-3972.D8349.2.patch, HIVE-3972.D8349.3.patch,
> Queries for fetching results which have lastly "order by" clause make final MR run with
single reducer, which can be too much. For example, 
> {code}
> select value, sum(key) as sum from src group by value order by sum;
> {code}
> If number of reducer is reasonable, multiple result files could be merged into single
sorted stream in the fetcher level.

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