[HIVE-549] Parallel Execution Mechanism

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.5.0
• Component/s: Query Processor
• Labels: hive-appu
• Hadoop Flags: Reviewed
• Release Note: Adds the feature of launching multiple map-reduce tasks that are not dependent on each other in parallel. Examples of queries affected would be those including union-alls, and trees of join operators.
• Assignee: Chaitanya Mishra
• Reporter: Adam Kramer
• Created: 08/Jun/09 07:45
• Updated: 06/Dec/13 16:52
• Resolved: 04/Dec/09 02:22

Description

In a massively parallel database system, it would be awesome to also parallelize some of the mapreduce phases that our data needs to go through.

One example that just occurred to me is UNION ALL: when you union two SELECT statements, effectively you could run those statements in parallel. There's no situation (that I can think of, but I don't have a formal proof) in which the left statement would rely on the right statement, or vice versa. So, they could be run at the same time...and perhaps they should be. Or, perhaps there should be a way to make this happen...PARALLEL UNION ALL? PUNION ALL?

Issue Links

• relates to: PIG-1734 Pig needs a more efficient DAG execution
• relates to: HIVE-1033 change default value of hive.exec.parallel to true