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https://issues.apache.org/jira/browse/HBASE-9272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13751855#comment-13751855
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Lars Hofhansl commented on HBASE-9272:
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So what do folks want to see from this? I have a version now that does RS round
robin and also reduces synchronization a bit by passing Exceptions as Result
subclasses through the Queue between the scanners and the reader thread.
I get the fairest scheduling by submitting single region tasks in RS round
robin order to a thread pool. The only down side is that the with this kind of
scheduling the outbounded pools used for other HTable operations cannot be used
here. I can work around that by pulling doing the task queuing myself outside
of the Threadpool.
Lastly a theme similar to this can be efficiently used for a sorted prefetching
scanner - one just spawnes off N threads this time in Region order, each
writing into their own queues, and then read them in order.
> 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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