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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9272) A simple parallel, unordered scanner
Date Sat, 07 Sep 2013 00:44:53 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13760813#comment-13760813
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Lars Hofhansl commented on HBASE-9272:
--------------------------------------

Thanks Ted.
The thread pool is always passes in, so ParallelClientScanner does not manage that in any
event. Yeah, interrupted status should be restored.
Also need a way to kill the other threads running when one threads throws an exception. Previously
I was using an exclusive thread pool, but now it is shared.

Will make a trunk patch too.
                
> A simple parallel, unordered scanner
> ------------------------------------
>
>                 Key: HBASE-9272
>                 URL: https://issues.apache.org/jira/browse/HBASE-9272
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>            Priority: Minor
>         Attachments: 9272-0.94.txt, 9272-0.94-v2.txt, ParallelClientScanner.java, ParallelClientScanner.java
>
>
> The contract of ClientScanner is to return rows in sort order. That limits the order
in which region can be scanned.
> I propose a simple ParallelScanner that does not have this requirement and queries regions
in parallel, return whatever gets returned first.
> This is generally useful for scans that filter a lot of data on the server, or in cases
where the client can very quickly react to the returned data.
> I have a simple prototype (doesn't do error handling right, and might be a bit heavy
on the synchronization side - it used a BlockingQueue to hand data between the client using
the scanner and the threads doing the scanning, it also could potentially starve some scanners
long enugh to time out at the server).
> On the plus side, it's only a 130 lines of code. :)

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