Github user dorx commented on a diff in the pull request:
https://github.com/apache/spark/pull/916#discussion_r13212134
--- Diff: core/src/main/scala/org/apache/spark/rdd/RDD.scala ---
@@ -421,6 +431,22 @@ abstract class RDD[T: ClassTag](
Utils.randomizeInPlace(samples, rand).take(total)
}
+ private[spark] def computeFraction(num: Int, total: Long,
withReplacement: Boolean) : Double = {
+ val fraction = num.toDouble / total
+ if (withReplacement) {
+ var numStDev = 5
+ if (num < 12) {
+ // special case to guarantee sample size for small s
+ numStDev = 9
+ }
+ fraction + numStDev * math.sqrt(fraction / total)
+ } else {
+ val delta = 0.00005
--- End diff --
actually success rate = 1-2*delta, so 0.00005 gives 99.99% success rate,
consistent with the poisson success rate.
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