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https://issues.apache.org/jira/browse/SPARK-21401?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16089424#comment-16089424
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Peng Meng commented on SPARK-21401:
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Hi [~srowen], for ALS optimization, the difference of using poll and sorted is
large:
When num = 20, if use sorted here, the prediction time is about 31s, if use
poll, the prediction time is about 26s. I think this difference is large. I
have tested many times. The result is about the same.
https://github.com/apache/spark/pull/18624.
I am testing LDA of changing sorted to poll.
> add poll function for BoundedPriorityQueue
> ------------------------------------------
>
> Key: SPARK-21401
> URL: https://issues.apache.org/jira/browse/SPARK-21401
> Project: Spark
> Issue Type: Improvement
> Components: ML, MLlib
> Affects Versions: 2.3.0
> Reporter: Peng Meng
> Priority: Minor
>
> The most of BoundedPriorityQueue usages in ML/MLLIB are:
> Get the value of BoundedPriorityQueue, then sort it.
> For example, in Word2Vec: pq.toSeq.sortBy(-_._2)
> in ALS, pq.toArray.sorted()
> The test results show using pq.poll() is much faster than sort the value.
> For example, in PR https://github.com/apache/spark/pull/18624
> We get the sorted value of pq by the following code:
> {quote}
> var size = pq.size
> while(size > 0) {
> size -= 1
> val factor = pq.poll
> }{quote}
> If using the generally used methods: pq.toArray.sorted() to get the sorted
> value of pq. There is about 10% performance reduction.
> It is good to add the poll function for BoundedPriorityQueue, since many
> usages of PQ need the sorted value.
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