[HIVE-3972] Support using multiple reducer for fetching order by results

• Type: Improvement
• Status: Patch Available
• Priority: Minor
• Resolution: Unresolved
• Component/s: Query Processor
• Assignee: Navis Ryu
• Reporter: Navis Ryu
• Created: 01/Feb/13 07:44
• Updated: 07/Jan/15 08:01

Description

Queries for fetching results which have lastly "order by" clause make final MR run with single reducer, which can be too much. For example,

select value, sum(key) as sum from src group by value order by sum;

If number of reducer is reasonable, multiple result files could be merged into single sorted stream in the fetcher level.