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https://issues.apache.org/jira/browse/HIVE-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13577502#comment-13577502
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Navis commented on HIVE-3972:
-----------------------------
[~ashutoshc] Above query has two RSs which means it consists of two MRs
(without HIVE-2340). And second MR still can be a target of top-K optimization.
But I've realized by your comment that this issue and HIVE-3562 are
complementary and should be merged into another one. Thanks.
And.. the limit configuration on fetch task is still active, which means
early-exit on fetch task is still possible without HIVE-3562. It's merge sort
on sorted streams, so it would not demand much of memory.
> 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
>
>
> 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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