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From "He Yongqiang (JIRA)" <>
Subject [jira] Commented: (HIVE-549) UNION ALL statements should be run in parallel
Date Mon, 08 Jun 2009 17:48:07 GMT


He Yongqiang commented on HIVE-549:

Since the generated tasks plan/task stages is a DAG, the user can get results more quickly
if we submitting tasks in parallel (two jobs can be submmitted in parallel if they/their parents
does not rely on each other)?  We can let hadoop scheduler how to run the jobs for better
cluster usage etc.

> UNION ALL statements should be run in parallel
> ----------------------------------------------
>                 Key: HIVE-549
>                 URL:
>             Project: Hadoop Hive
>          Issue Type: Wish
>          Components: Query Processor
>            Reporter: Adam Kramer
> 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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