Seth Hendrickson created SPARK-19746:
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Summary: 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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