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https://issues.apache.org/jira/browse/HIVE-549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13841408#comment-13841408
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Ashutosh Chauhan commented on HIVE-549:
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This should be turned on by default. [~asimjalis] Would you like to create a
jira to change the default value for this config?
> Parallel Execution Mechanism
> ----------------------------
>
> Key: HIVE-549
> URL: https://issues.apache.org/jira/browse/HIVE-549
> Project: Hive
> Issue Type: New Feature
> Components: Query Processor
> Reporter: Adam Kramer
> Assignee: Chaitanya Mishra
> Labels: hive-appu
> Fix For: 0.5.0
>
> Attachments: HIVE549-v7.patch
>
>
> 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?
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