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https://issues.apache.org/jira/browse/HBASE-7180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13499911#comment-13499911
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Lars Hofhansl commented on HBASE-7180:
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With this patch a RegionObserver wrapping a RegionScanner in preScannerOpen can
handle the readpoint and start/close region operation itself and then call the
cheaper next() on the wrapped scanner when needed.
> RegionScannerImpl.next() is inefficient.
> ----------------------------------------
>
> Key: HBASE-7180
> URL: https://issues.apache.org/jira/browse/HBASE-7180
> Project: HBase
> Issue Type: Bug
> Reporter: Lars Hofhansl
> Attachments: 7180-0.94-SKETCH.txt
>
>
> We just came across a special scenario.
> For our Phoenix project (SQL runtime for HBase), we push a lot of work into
> HBase via coprocessors. One method is to wrap RegionScanner in coprocessor
> hooks and then do processing in the hook to avoid returning a lot of data to
> the client unnecessarily.
> In this specific case this is pretty bad. Since the wrapped RegionScanner's
> next() does not "know" that it is called this way is still does all of this
> on each invocation:
> # Starts a RegionOperation
> # Increments the request count
> # set the current read point on a thread local (because generally each call
> could come from a different thread)
> # Finally does the next on its StoreScanner(s)
> # Ends the RegionOperation
> When this is done in a tight loop millions of times (as is the case for us)
> it starts to become significant.
> Not sure what to do about this, really. Opening this issue for discussion.
> One way is to extend the RegionScanner with an "internal" next() method of
> sorts, so that all this overhead can be avoided. The coprocessor could call
> the regular next() methods once and then just call the cheaper internal
> version.
> Are there better/cleaner ways?
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