[jira] [Commented] (SPARK-19746) LogisticAggregator is inefficient in indexing

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-19746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15885159#comment-15885159 ] 

Apache Spark commented on SPARK-19746:
--------------------------------------

User 'sethah' has created a pull request for this issue:
https://github.com/apache/spark/pull/17078

> LogisticAggregator is inefficient in indexing
> ---------------------------------------------
>
>                 Key: SPARK-19746
>                 URL: https://issues.apache.org/jira/browse/SPARK-19746
>             Project: Spark
>          Issue Type: Improvement
>          Components: ML
>    Affects Versions: 2.1.0
>            Reporter: Seth Hendrickson
>
> The following code occurs in the `LogisticAggregator.add` method, which is a performance critical path.
> {code}
> val localCoefficients = bcCoefficients.value
> features.foreachActive { (index, value) =>
>       val stdValue = value / localFeaturesStd(index)
>       var j = 0
>       while (j < numClasses) {
>         margins(j) += localCoefficients(index * numClasses + j) * stdValue
>         j += 1
>       }
>     }
> {code}
> `llocalCoefficients(index * numClasses + j)` calls the `apply` method on `Vector`, which dispatches to `asBreeze(index * numClasses + j)` which creates a new Breeze vector, and then indexes it. This is very inefficient, creates a lot of unnecessary garbage, and we can avoid it by indexing the underlying array.



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