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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-7180) RegionScannerImpl.next() is inefficient.
Date Sun, 18 Nov 2012 06:40:12 GMT
Lars Hofhansl created HBASE-7180:
------------------------------------

             Summary: RegionScannerImpl.next() is inefficient.
                 Key: HBASE-7180
                 URL: https://issues.apache.org/jira/browse/HBASE-7180
             Project: HBase
          Issue Type: Bug
            Reporter: Lars Hofhansl


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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