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https://issues.apache.org/jira/browse/HBASE-9272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13760723#comment-13760723
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Ted Yu commented on HBASE-9272:
-------------------------------
{code}
+ for (Iterator<Map.Entry<HRegionLocation, Queue<Scan>>> it =
tasks.entrySet().iterator(); it.hasNext();) {
+ Scan next = it.next().getValue().poll();
+ if (next == null) {
+ it.remove();
{code}
If there is more than 1 Scan for a Queue (for some HRegionLocation), would the
second and sequent Scan's be skipped due to call to it.next() above ?
> 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, 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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