[SPARK-10930] History "Stages" page "duration" can be confusing

Author: Derek Dagit <derekd@yahoo-inc.com>

Closes #9051 from d2r/spark-10930-ui-max-task-dur.

core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala

@@ -145,9 +145,22 @@ private[ui] class StageTableBase(
       case None => "Unknown"
     }
     val finishTime = s.completionTime.getOrElse(System.currentTimeMillis)
-    val duration = s.submissionTime.map { t =>
-      if (finishTime > t) finishTime - t else System.currentTimeMillis - t
-    }
+
+    // The submission time for a stage is misleading because it counts the time
+    // the stage waits to be launched. (SPARK-10930)
+    val taskLaunchTimes =
+      stageData.taskData.values.map(_.taskInfo.launchTime).filter(_ > 0)
+    val duration: Option[Long] =
+      if (taskLaunchTimes.nonEmpty) {
+        val startTime = taskLaunchTimes.min
+        if (finishTime > startTime) {
+          Some(finishTime - startTime)
+        } else {
+          Some(System.currentTimeMillis() - startTime)
+        }
+      } else {
+        None
+      }
     val formattedDuration = duration.map(d => UIUtils.formatDuration(d)).getOrElse("Unknown")
 
     val inputRead = stageData.inputBytes