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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-549) UNION ALL statements should be run in parallel
Date Mon, 08 Jun 2009 18:26:07 GMT

    [ https://issues.apache.org/jira/browse/HIVE-549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12717354#action_12717354
] 

Namit Jain commented on HIVE-549:
---------------------------------

I agree completely - What I was trying to get at is
1. It is not specific to union all.
2. It does not need a change in compiler - just the scheduler change should be good enough.

> UNION ALL statements should be run in parallel
> ----------------------------------------------
>
>                 Key: HIVE-549
>                 URL: https://issues.apache.org/jira/browse/HIVE-549
>             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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