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From "Chaitanya Mishra (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-549) Parallel Execution Mechanism
Date Fri, 23 Oct 2009 20:29:59 GMT

    [ https://issues.apache.org/jira/browse/HIVE-549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12769413#action_12769413
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Chaitanya Mishra commented on HIVE-549:
---------------------------------------

Zheng and I had a email-discussion on this. To launch multiple tasks from the same driver,
we'll need to launch each task as a separate thread.

The simplest solution is to extend Task to implement the Runnable Interface, but this might
affect other components... Not completely sure about this since an element that implements
runnable can still be called in a sequential fashion.

Zheng instead proposes adding a new class TaskRunner, with functions:

run(): asynchronous call
start(),
wait(long timeoutMilli),
and stop()

Most likely, if we get taskrunner to extend Thread, we get these functions; if not we can
implement runnable.

So, do we get Task to implement runnable, or add a layer of indirection as TaskRunner? 

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