[SPARK-2533] Add locality levels on stage summary view

Author: Jean-Baptiste Onofré <jbonofre@apache.org>

Closes #9487 from jbonofre/SPARK-2533-2.

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

@@ -28,7 +28,7 @@ import org.apache.commons.lang3.StringEscapeUtils
 
 import org.apache.spark.{InternalAccumulator, SparkConf}
 import org.apache.spark.executor.TaskMetrics
-import org.apache.spark.scheduler.{AccumulableInfo, TaskInfo}
+import org.apache.spark.scheduler.{AccumulableInfo, TaskInfo, TaskLocality}
 import org.apache.spark.ui._
 import org.apache.spark.ui.jobs.UIData._
 import org.apache.spark.util.{Utils, Distribution}
@@ -70,6 +70,21 @@ private[ui] class StagePage(parent: StagesTab) extends WebUIPage("stage") {
 
   private val displayPeakExecutionMemory = parent.conf.getBoolean("spark.sql.unsafe.enabled", true)
 
+  private def getLocalitySummaryString(stageData: StageUIData): String = {
+    val localities = stageData.taskData.values.map(_.taskInfo.taskLocality)
+    val localityCounts = localities.groupBy(identity).mapValues(_.size)
+    val localityNamesAndCounts = localityCounts.toSeq.map { case (locality, count) =>
+      val localityName = locality match {
+        case TaskLocality.PROCESS_LOCAL => "Process local"
+        case TaskLocality.NODE_LOCAL => "Node local"
+        case TaskLocality.RACK_LOCAL => "Rack local"
+        case TaskLocality.ANY => "Any"
+      }
+      s"$localityName: $count"
+    }
+    localityNamesAndCounts.sorted.mkString("; ")
+  }
+
   def render(request: HttpServletRequest): Seq[Node] = {
     progressListener.synchronized {
       val parameterId = request.getParameter("id")
@@ -129,6 +144,10 @@ private[ui] class StagePage(parent: StagesTab) extends WebUIPage("stage") {
               <strong>Total Time Across All Tasks: </strong>
               {UIUtils.formatDuration(stageData.executorRunTime)}
             </li>
+            <li>
+              <strong>Locality Level Summary: </strong>
+              {getLocalitySummaryString(stageData)}
+            </li>
             {if (stageData.hasInput) {
               <li>
                 <strong>Input Size / Records: </strong>