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https://issues.apache.org/jira/browse/HIVE-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13781628#comment-13781628
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Navis commented on HIVE-3972:
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[~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 form.
HIVE-3972 is HIVE-4002 for order-by.
> Support using multiple reducer for fetching order by results
> ------------------------------------------------------------
>
> Key: HIVE-3972
> URL: https://issues.apache.org/jira/browse/HIVE-3972
> 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, HIVE-3972.D8349.4.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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