Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/5608#discussion_r29100295
--- Diff: core/src/main/scala/org/apache/spark/util/SizeEstimator.scala ---
@@ -204,25 +204,36 @@ private[spark] object SizeEstimator extends Logging {
}
} else {
// Estimate the size of a large array by sampling elements without
replacement.
- var size = 0.0
+ // To exclude the shared objects that the array elements may link,
sample twice
+ // and use the min one to caculate array size.
val rand = new Random(42)
- val drawn = new OpenHashSet[Int](ARRAY_SAMPLE_SIZE)
- var numElementsDrawn = 0
- while (numElementsDrawn < ARRAY_SAMPLE_SIZE) {
- var index = 0
- do {
- index = rand.nextInt(length)
- } while (drawn.contains(index))
- drawn.add(index)
- val elem = ScalaRunTime.array_apply(array,
index).asInstanceOf[AnyRef]
- size += SizeEstimator.estimate(elem, state.visited)
- numElementsDrawn += 1
- }
- state.size += ((length / (ARRAY_SAMPLE_SIZE * 1.0)) * size).toLong
+ val drawn = new OpenHashSet[Int](2 * ARRAY_SAMPLE_SIZE)
--- End diff --
Oh right, I am mixing up these two constants. It's fine. I still suspect
this could be parameterized to sample N times, and simpler with replacement,
but it's not essential.
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