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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-9272) A simple parallel, unordered scanner
Date Tue, 10 Sep 2013 21:42:53 GMT

     [ https://issues.apache.org/jira/browse/HBASE-9272?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Lars Hofhansl updated HBASE-9272:
---------------------------------

    Attachment: 9272-0.94-v3.txt

Patch with fewer API changes.
Still need to do exception handling.
I'll probably go back to the earlier version of having a dedicated threadpool for a parallel
scanner, for three reasons:
# It's easy to kill all outstanding tasks on dedicated pool
# This is for long running scans anyway, so the cost of a dedicated pool is amortized nicely.
# The scanning does not interfere with the other (more latency sensitive - such as MultiGet)
operations.

Will also make a trunk patch soon. Promised.
                
> 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, 9272-0.94-v3.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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