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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-549) Parallel Execution Mechanism
Date Tue, 01 Dec 2009 20:27:20 GMT

    [ https://issues.apache.org/jira/browse/HIVE-549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12784400#action_12784400
] 

Zheng Shao commented on HIVE-549:
---------------------------------

We cannot use JobControl because not all Hive tasks are map-reduce jobs.

In some sense, Driver is reimplementing JobControl to accomodate all different types of Hive
tasks. The alternative is to extend JobControl.
I think implementing Driver from scratch (as we already did) is more flexible at this point
of time.

This is good information though. At some point we should revisit Driver and JobControl to
see how we can refactor the code better.


> Parallel Execution Mechanism
> ----------------------------
>
>                 Key: HIVE-549
>                 URL: https://issues.apache.org/jira/browse/HIVE-549
>             Project: Hadoop Hive
>          Issue Type: Wish
>          Components: Query Processor
>    Affects Versions: 0.3.0
>            Reporter: Adam Kramer
>            Assignee: Chaitanya Mishra
>         Attachments: HIVE549-v6.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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