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https://issues.apache.org/jira/browse/HBASE-9272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13745205#comment-13745205
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Lars Hofhansl commented on HBASE-9272:
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More like a MultiGet that farms requests out to multiple RegionServers at the
same time, although I am using a different threading model (fixed number of
threads and an unbounded waiting queue, rather than the reverse).
There are a lot of options. Right now each region becomes a task and is
scheduled on a threadpool. Could also group by regionserver.
Obviously this only makes sense when the scan will touch a "reasonable" number
of a regions.
> 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
> Priority: Minor
>
> 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 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 scanner, 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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