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https://issues.apache.org/jira/browse/MAHOUT-881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13149270#comment-13149270
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Sean Owen commented on MAHOUT-881:
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Since it's easy, I just used jprofiler to observe the exact difference. See
attached excerpt from the call graph, before and after. Out of about 23 minutes
of CPU time spent in the getTopItems() method, the cost of queue operations did
in fact drop, from 90 microseconds to 47 microseconds. That's 0.0065% of
runtime before, or about 1 part in 15,000, so I don't think you are observing
any actual difference in runtime.
I'm not against this; I suppose that if it's not adding what we thought and is
introducing very slightly more complexity and change, I'd be very slightly
predisposed to not make such a change. Or what about addressing some of those
allocations directly that Yonik mentioned, if anything? Those are 1-liners.
In any event, I would rather not also change AbstractAverageDifferenceEvaluator
-- was that just a temp change? Or I could work in reporting those figures
differently for you. To answer your TODO: returning an array would change the
API, and cause some other difficult breakage (IIRC). It's a List on purpose. I
think you'll find however that Arrays.asList() is the better method call there,
probably avoids overhead.
> Refactor TopItems to use Lucene's PriorityQueue and remove excessive sorting
> ----------------------------------------------------------------------------
>
> Key: MAHOUT-881
> URL: https://issues.apache.org/jira/browse/MAHOUT-881
> Project: Mahout
> Issue Type: Improvement
> Affects Versions: 0.6
> Reporter: Grant Ingersoll
> Assignee: Grant Ingersoll
> Priority: Minor
> Attachments: Call_Tree.html, Call_Tree_2.html, MAHOUT-881.patch,
> MAHOUT-881.patch, MAHOUT-881.patch
>
>
> TopItems.getTop*() all do a fair number of excessive operations that can be
> replaced by switching to using Lucene's PriorityQueue implementation, which
> is more efficient and faster than Java's built in PQ implementation.
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