[SPARK-17672] Spark 2.0 history server web Ui takes too long for a single application

Added a new API getApplicationInfo(appId: String) in class ApplicationHistoryProvider and class SparkUI to get app info. In this change, FsHistoryProvider can directly fetch one app info in O(1) time complexity compared to O(n) before the change which used an Iterator.find() interface.

Both ApplicationCache and OneApplicationResource classes adopt this new api.

 manual tests

Author: Gang Wu <wgtmac@uber.com>

Closes #15247 from wgtmac/SPARK-17671.

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

@@ -109,4 +109,9 @@ private[history] abstract class ApplicationHistoryProvider {
   @throws(classOf[SparkException])
   def writeEventLogs(appId: String, attemptId: Option[String], zipStream: ZipOutputStream): Unit
 
+  /**
+   * @return the [[ApplicationHistoryInfo]] for the appId if it exists.
+   */
+  def getApplicationInfo(appId: String): Option[ApplicationHistoryInfo]
+
 }

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

@@ -224,6 +224,10 @@ private[history] class FsHistoryProvider(conf: SparkConf, clock: Clock)
 
   override def getListing(): Iterable[FsApplicationHistoryInfo] = applications.values
 
+  override def getApplicationInfo(appId: String): Option[FsApplicationHistoryInfo] = {
+    applications.get(appId)
+  }
+
   override def getAppUI(appId: String, attemptId: Option[String]): Option[LoadedAppUI] = {
     try {
       applications.get(appId).flatMap { appInfo =>

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

@@ -182,6 +182,10 @@ class HistoryServer(
     getApplicationList().iterator.map(ApplicationsListResource.appHistoryInfoToPublicAppInfo)
   }
 
+  def getApplicationInfo(appId: String): Option[ApplicationInfo] = {
+    provider.getApplicationInfo(appId).map(ApplicationsListResource.appHistoryInfoToPublicAppInfo)
+  }
+
   override def writeEventLogs(
       appId: String,
       attemptId: Option[String],

core/src/main/scala/org/apache/spark/status/api/v1/ApiRootResource.scala

@@ -222,6 +222,7 @@ private[spark] object ApiRootResource {
 private[spark] trait UIRoot {
   def getSparkUI(appKey: String): Option[SparkUI]
   def getApplicationInfoList: Iterator[ApplicationInfo]
+  def getApplicationInfo(appId: String): Option[ApplicationInfo]
 
   /**
    * Write the event logs for the given app to the [[ZipOutputStream]] instance. If attemptId is

core/src/main/scala/org/apache/spark/status/api/v1/OneApplicationResource.scala

@@ -24,7 +24,7 @@ private[v1] class OneApplicationResource(uiRoot: UIRoot) {
 
   @GET
   def getApp(@PathParam("appId") appId: String): ApplicationInfo = {
-    val apps = uiRoot.getApplicationInfoList.find { _.id == appId }
+    val apps = uiRoot.getApplicationInfo(appId)
     apps.getOrElse(throw new NotFoundException("unknown app: " + appId))
   }
 

core/src/main/scala/org/apache/spark/ui/SparkUI.scala

@@ -126,6 +126,10 @@ private[spark] class SparkUI private (
       ))
     ))
   }
+
+  def getApplicationInfo(appId: String): Option[ApplicationInfo] = {
+    getApplicationInfoList.find(_.id == appId)
+  }
 }
 
 private[spark] abstract class SparkUITab(parent: SparkUI, prefix: String)