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https://issues.apache.org/jira/browse/MAHOUT-881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13149111#comment-13149111
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Yonik Seeley commented on MAHOUT-881:
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bq. Why are there fewer operations? Both seem to do an insert if the new item
is known to be among the new top-N, and not otherwise.
Assuming a full priority queue, you have an add() and a poll() per competitive
entry (I don't think there's a way to get around that using Java's PQ).
Lucene's PQ can rebalance the heap once per competitive entry.
bq. I have an unfounded suspicion that the implicit heap sort here is slower in
practice here than a simple quicksort, since that is generally the case.
Heapsort is generally slower than quicksort... but since we already have a
built heap, we're only doing half-a-heapsort?
> 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: 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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