Github user zsxwing commented on a diff in the pull request:
https://github.com/apache/spark/pull/19763#discussion_r151801570
--- Diff: core/src/main/scala/org/apache/spark/MapOutputTracker.scala ---
@@ -473,16 +477,41 @@ private[spark] class MapOutputTrackerMaster(
}
/**
+ * Try to equally divide Range(0, num) to divisor slices
+ */
+ def equallyDivide(num: Int, divisor: Int): Iterator[Seq[Int]] = {
+ assert(divisor > 0, "Divisor should be positive")
+ val (each, remain) = (num / divisor, num % divisor)
+ val (smaller, bigger) = (0 until num).splitAt((divisor-remain) * each)
+ if (each != 0) {
+ smaller.grouped(each) ++ bigger.grouped(each + 1)
+ } else {
+ bigger.grouped(each + 1)
+ }
+ }
+
+ /**
* Return statistics about all of the outputs for a given shuffle.
*/
def getStatistics(dep: ShuffleDependency[_, _, _]): MapOutputStatistics
= {
shuffleStatuses(dep.shuffleId).withMapStatuses { statuses =>
val totalSizes = new Array[Long](dep.partitioner.numPartitions)
- for (s <- statuses) {
- for (i <- 0 until totalSizes.length) {
- totalSizes(i) += s.getSizeForBlock(i)
- }
+ val mapStatusSubmitTasks = ArrayBuffer[Future[_]]()
+ var taskSlices = parallelism
+
+ equallyDivide(totalSizes.length, taskSlices).foreach {
+ reduceIds =>
+ mapStatusSubmitTasks += threadPoolMapStats.submit(
+ new Runnable {
+ override def run(): Unit = {
+ for (s <- statuses; i <- reduceIds) {
+ totalSizes(i) += s.getSizeForBlock(i)
+ }
+ }
+ }
+ )
}
+ mapStatusSubmitTasks.foreach(_.get())
--- End diff --
Don't use `scala.concurrent.ExecutionContext.Implicits.global`. You need to
create a thread pool.
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