[GitHub] [spark] Ngone51 commented on a change in pull request #23677: [SPARK-26755][SCHEDULER] : Optimize Spark Scheduler to dequeue speculative tasks…

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Ngone51 commented on a change in pull request #23677: [SPARK-26755][SCHEDULER] : Optimize Spark Scheduler to dequeue speculative tasks…
URL: https://github.com/apache/spark/pull/23677#discussion_r303004365
 
 

 ##########
 File path: core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
 ##########
 @@ -302,15 +272,18 @@ private[spark] class TaskSetManager(
   private def dequeueTaskFromList(
       execId: String,
       host: String,
-      list: ArrayBuffer[Int]): Option[Int] = {
+      list: ArrayBuffer[Int],
+      speculative: Boolean = false): Option[Int] = {
     var indexOffset = list.size
     while (indexOffset > 0) {
       indexOffset -= 1
       val index = list(indexOffset)
-      if (!isTaskBlacklistedOnExecOrNode(index, execId, host)) {
+      if (!isTaskBlacklistedOnExecOrNode(index, execId, host) &&
+        !(speculative && hasAttemptOnHost(index, host))) {
         // This should almost always be list.trimEnd(1) to remove tail
         list.remove(indexOffset)
-        if (copiesRunning(index) == 0 && !successful(index)) {
+        if (((copiesRunning(index) < 2 && speculative) ||
+          (!speculative && copiesRunning(index) == 0)) && !successful(index)) {
 
 Review comment:
   How about this ?
   
   ```
   if (!successful(index)) {
     if (copiesRunning(index) == 0) {
       return Some(index)
     } else if (speculative && copiesRunning(index) == 1) {
       return Some(index)
     }
   }
   ```
   
   One important reason is that speculation default to be false.

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