Github user jodersky commented on a diff in the pull request:
https://github.com/apache/spark/pull/14359#discussion_r72322067
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala ---
@@ -1110,4 +1124,40 @@ private[spark] object RandomForest extends Logging {
}
}
+ /**
+ * Class for queueing nodes to split on each iteration.
+ * This is a FILO queue.
+ */
+ private[impl] class NodeQueue {
+ private var q: mutable.MutableList[(Int, LearningNode)] =
+ mutable.MutableList.empty[(Int, LearningNode)]
+
+ /** Put (treeIndex, node) into queue. Constant time. */
+ def put(treeIndex: Int, node: LearningNode): Unit = {
+ q += ((treeIndex, node))
+ }
+
+ /** Remove and return last inserted element. Linear time (unclear in
Scala docs though) */
--- End diff --
How critical is this for performance? I know that `append` is O(1) for
scala mutable lists but `dropRight(1)` is actually implemented in a parent
class [1] of `MutableList` and therefores does not take advantage of the list's
reference to its last element. All in all, from it's implementation it seems
that `dropRight` is O(n)
[1]
https://github.com/scala/scala/blob/v2.11.8/src/library/scala/collection/LinearSeqOptimized.scala#L194-L204
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