srowen commented on a change in pull request #23983: [SPARK-26881][mllib]
Heuristic for tree aggregate depth
URL: https://github.com/apache/spark/pull/23983#discussion_r263851419
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File path:
mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/RowMatrix.scala
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@@ -117,6 +117,7 @@ class RowMatrix @Since("1.0.0") (
// Computes n*(n+1)/2, avoiding overflow in the multiplication.
// This succeeds when n <= 65535, which is checked above
val nt = if (n % 2 == 0) ((n / 2) * (n + 1)) else (n * ((n + 1) / 2))
+ val gramianSizeInMb = (nt / 1000000) * 8
Review comment:
These are integers though. (999999/1000000)*8 == 0, but (999999*8)/1000000
== 7, which is more like correct. It has to be done using longs though to avoid
overflow: `((nt * 8L) / 1000000).toInt`
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