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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-9272) A simple parallel, unordered scanner
Date Wed, 21 Aug 2013 21:06:53 GMT

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

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

    Attachment: ParallelClientScanner.java

A little cleanup. Deals with exceptions now (retrows only the first one).

Note: This is client side only, using only public HBase interfaces, so this does not need
to be part of HBase.

Also re: the 1.5% this happens only when you use ParallelScanner with a single thread, should
use ClientScanner (what HTable.getScanner returns) in that case anyway.

                
> 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: 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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