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https://issues.apache.org/jira/browse/HBASE-1935?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770087#action_12770087
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Jonathan Gray commented on HBASE-1935:
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Went over the patch twice. Looks pretty good.
There is some cross-over with work done in Multi operations (MultiGet,
MultiDelete, etc..). I think the first thing to decide is if we want to create
some unified threading system or take passed-in ExecutorServices as is done
with the patch. And do we need a special ParallelHTable, or should the normal
HTable support threading? I believe the latter.
At either the HCM or HTable level, I think we should have a local, bounded
ExecutorService pool. You would be able to modify its size through the
constructor, but default settings would come from something in the conf like
hbase.client.threads.
One thing I do like (at least for early versions of threaded clients) is just
failing immediately when encountering a problem like a split. Properly
handling this is one of the hardest parts about this (and other things like
stateful filters), and retries are tricky and imperfect. With batched/parallel
reads (get or scan) we should just fail-fast and throw exceptions to let the
client deal. With batched/parallel writes (put or delete) we should process
what we can and return back to the client what was not completed.
Another thing I'm a little confused about... this seems to be designed for
completely out-of-order receipt of results. Rather than aggregating up a list
of Futures, and then waiting for them to complete in order, this uses a
ExecutorCompletionService which returns things as they finish. I can see in
certain use cases this would make sense, but is a bit more limited. However, I
don't see why we can't support both using two different task completion-waiting
paths and with very small changes to the constructor APIs.
> Scan in parallel
> ----------------
>
> Key: HBASE-1935
> URL: https://issues.apache.org/jira/browse/HBASE-1935
> Project: Hadoop HBase
> Issue Type: New Feature
> Reporter: stack
> Attachments: pscanner.patch
>
>
> A scanner that rather than scan in series, instead scanned multiple regions
> in parallell would be more involved but could complete much faster
> partiularly if results are sparse.
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