[GitHub] [spark] vanzin commented on a change in pull request #24245: [SPARK-13704][CORE][YARN] Reduce rack resolution time

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vanzin commented on a change in pull request #24245: [SPARK-13704][CORE][YARN] Reduce rack resolution time
URL: https://github.com/apache/spark/pull/24245#discussion_r271444178
 
 

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 File path: core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
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 @@ -186,8 +186,23 @@ private[spark] class TaskSetManager(
 
   // Add all our tasks to the pending lists. We do this in reverse order
   // of task index so that tasks with low indices get launched first.
-  for (i <- (0 until numTasks).reverse) {
-    addPendingTask(i)
+  addPendingTasks()
+
+  private def addPendingTasks(): Unit = {
+    val (_, duration) = Utils.timeTakenMs {
+      for (i <- (0 until numTasks).reverse) {
+        addPendingTask(i, resolveRacks = false)
+      }
+      // Resolve the rack for each host. This can be slow, so de-dupe the list of hosts,
+      // and assign the rack to all relevant task indices.
+      val racks = sched.getRacksForHosts(pendingTasksForHost.keySet.toSeq)
 
 Review comment:
   There's an implicit assumption here that `map.keySet` and `map.values` iterate in the same order. I'm not sure if that's guaranteed, and at the same time I don't see why that wouldn't be the case, but just wanted to point this out.

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