if app isnt found, reload apps from FS before giving up

Author: squito

core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala

@@ -148,7 +148,11 @@ private[history] class FsHistoryProvider(conf: SparkConf) extends ApplicationHis
 
   override def getAppUI(appId: String): Option[SparkUI] = {
     try {
-      applications.get(appId).map { info =>
+      val appOpt = applications.get(appId).orElse {
+        getListing(true)
+        applications.get(appId)
+      }
+      appOpt.map { info =>
         val replayBus = new ReplayListenerBus()
         val ui = {
           val conf = this.conf.clone()

core/src/main/scala/org/apache/spark/deploy/history/HistoryServer.scala

@@ -53,7 +53,7 @@ class HistoryServer(
 
   private val appLoader = new CacheLoader[String, SparkUI] {
     override def load(key: String): SparkUI = {
-      val ui = provider.getAppUI(key).getOrElse(throw new NoSuchElementException())
+      val ui = provider.getAppUI(key).getOrElse(throw new NoSuchElementException(s"no app with key $key"))
       attachSparkUI(ui)
       ui
     }