Separate history server from history backend.

This change does two things, mainly:

- Separate the logic of serving application history from fetching
  application history from the underlying storage. Not only this
  cleans up the code a little bit, but it also serves as initial
  work for SPARK-1537, where we may want to fetch application data
  from Yarn instead of HDFS.

  I've kept the current command line options working, but I changed
  the way configuration is set to be mostly based on SparkConf,
  so that it's easy to support new providers later.

- Make it so the UI for each application is loaded lazily. The
  UIs are cached in memory (cache size configurable) for faster
  subsequent access. This means that we don't need a limit for
  the number of applications listed; the list should fit
  comfortably in memory (since it holds much less data).

  Because of this I lowered the number of applications kept in
  memory to 50 (since that setting doesn't influence the number
  of apps listed anymore).

Later, we may want to provide paging in the listing UI, and also
spilling the listing to disk and loading it on demand to avoid
large memory usage / slow startup.

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

@@ -0,0 +1,205 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.deploy.history
+
+import java.io.FileNotFoundException
+import java.util.concurrent.atomic.AtomicReference
+
+import scala.collection.mutable
+
+import org.apache.hadoop.fs.{FileStatus, Path}
+
+import org.apache.spark.{Logging, SecurityManager, SparkConf}
+import org.apache.spark.scheduler._
+import org.apache.spark.ui.SparkUI
+import org.apache.spark.util.Utils
+
+class FsHistoryProvider(conf: SparkConf) extends ApplicationHistoryProvider
+  with Logging {
+
+  // Interval between each check for event log updates
+  private val UPDATE_INTERVAL_MS = conf.getInt("spark.history.fs.updateInterval", 10) * 1000
+
+  private val logDir = conf.get("spark.history.fs.logDirectory")
+  private val fs = Utils.getHadoopFileSystem(logDir)
+
+  // A timestamp of when the disk was last accessed to check for log updates
+  private var lastLogCheckTime = -1L
+
+  // List of applications, in order from newest to oldest.
+  private val appList = new AtomicReference[Seq[ApplicationHistoryInfo]](Nil)
+
+  /**
+   * A background thread that periodically checks for event log updates on disk.
+   *
+   * If a log check is invoked manually in the middle of a period, this thread re-adjusts the
+   * time at which it performs the next log check to maintain the same period as before.
+   *
+   * TODO: Add a mechanism to update manually.
+   */
+  private val logCheckingThread = new Thread("LogCheckingThread") {
+    override def run() = Utils.logUncaughtExceptions {
+      while (!stopped) {
+        val now = System.currentTimeMillis
+        if (now - lastLogCheckTime > UPDATE_INTERVAL_MS) {
+          Thread.sleep(UPDATE_INTERVAL_MS)
+        } else {
+          // If the user has manually checked for logs recently, wait until
+          // UPDATE_INTERVAL_MS after the last check time
+          Thread.sleep(lastLogCheckTime + UPDATE_INTERVAL_MS - now)
+        }
+        checkForLogs()
+      }
+    }
+  }
+
+  @volatile private var stopped = false
+
+  initialize()
+
+  private def initialize() {
+    // Validate the log directory.
+    val path = new Path(logDir)
+    if (!fs.exists(path)) {
+      throw new IllegalArgumentException("Logging directory specified does not exist: %s".format(logDir))
+    }
+    if (!fs.getFileStatus(path).isDir) {
+      throw new IllegalArgumentException("Logging directory specified is not a directory: %s".format(logDir))
+    }
+
+    checkForLogs()
+    logCheckingThread.start()
+  }
+
+  override def stop() = {
+    stopped = true
+    logCheckingThread.interrupt()
+    logCheckingThread.join()
+  }
+
+  override def getListing(offset: Int, limit: Int): Seq[ApplicationHistoryInfo] = {
+    appList.get()
+  }
+
+  override def getAppInfo(appId: String): ApplicationHistoryInfo = {
+    try {
+      val appLogDir = fs.getFileStatus(new Path(logDir, appId))
+      loadAppInfo(appLogDir, true)
+    } catch {
+      case e: FileNotFoundException => null
+    }
+  }
+
+  /**
+   * Check for any updates to event logs in the base directory. This is only effective once
+   * the server has been bound.
+   *
+   * If a new completed application is found, the server renders the associated SparkUI
+   * from the application's event logs, attaches this UI to itself, and stores metadata
+   * information for this application.
+   *
+   * If the logs for an existing completed application are no longer found, the server
+   * removes all associated information and detaches the SparkUI.
+   */
+  def checkForLogs() = synchronized {
+    lastLogCheckTime = System.currentTimeMillis
+    logDebug("Checking for logs. Time is now %d.".format(lastLogCheckTime))
+    try {
+      val logStatus = fs.listStatus(new Path(logDir))
+      val logDirs = if (logStatus != null) logStatus.filter(_.isDir).toSeq else Seq[FileStatus]()
+      val logInfos = logDirs
+        .sortBy { dir => getModificationTime(dir) }
+        .filter {
+            dir => fs.isFile(new Path(dir.getPath(), EventLoggingListener.APPLICATION_COMPLETE))
+          }
+
+      var currentApps = Map[String, ApplicationHistoryInfo](
+        appList.get().map(app => (app.id -> app)):_*)
+
+      // For any application that either (i) is not listed or (ii) has changed since the last time
+      // the listing was created (defined by the log dir's modification time), load the app's info.
+      // Otherwise just reuse what's already in memory.
+      appList.set(logInfos
+        .map { dir =>
+          val curr = currentApps.getOrElse(dir.getPath().getName(), null)
+          if (curr == null || curr.lastUpdated < getModificationTime(dir)) {
+            loadAppInfo(dir, false)
+          } else {
+            curr
+          }
+        }
+        .sortBy { info => -info.lastUpdated })
+    } catch {
+      case t: Throwable => logError("Exception in checking for event log updates", t)
+    }
+  }
+
+  /**
+   * Parse the application's logs to find out the information we need to build the
+   * listing page.
+   */
+  private def loadAppInfo(logDir: FileStatus, renderUI: Boolean): ApplicationHistoryInfo = {
+    val elogInfo = EventLoggingListener.parseLoggingInfo(logDir.getPath(), fs)
+    val path = logDir.getPath
+    val appId = path.getName
+    val replayBus = new ReplayListenerBus(elogInfo.logPaths, fs, elogInfo.compressionCodec)
+    val appListener = new ApplicationEventListener
+    replayBus.addListener(appListener)
+
+    val ui: SparkUI = if (renderUI) {
+        val conf = this.conf.clone()
+        val appSecManager = new SecurityManager(conf)
+        new SparkUI(conf, appSecManager, replayBus, appId, "/history/" + appId)
+        // Do not call ui.bind() to avoid creating a new server for each application
+      } else {
+        null
+      }
+
+    replayBus.replay()
+    val appName = appListener.appName
+    val sparkUser = appListener.sparkUser
+    val startTime = appListener.startTime
+    val endTime = appListener.endTime
+    val lastUpdated = getModificationTime(logDir)
+    ApplicationHistoryInfo(appId,
+      appListener.appName,
+      appListener.startTime,
+      appListener.endTime,
+      getModificationTime(logDir),
+      appListener.sparkUser,
+      if (renderUI) appListener.viewAcls else null,
+      ui)
+  }
+
+  /** Return when this directory was last modified. */
+  private def getModificationTime(dir: FileStatus): Long = {
+    try {
+      val logFiles = fs.listStatus(dir.getPath)
+      if (logFiles != null && !logFiles.isEmpty) {
+        logFiles.map(_.getModificationTime).max
+      } else {
+        dir.getModificationTime
+      }
+    } catch {
+      case t: Throwable =>
+        logError("Exception in accessing modification time of %s".format(dir.getPath), t)
+        -1L
+    }
+  }
+
+}

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

@@ -26,19 +26,16 @@ import org.apache.spark.ui.{WebUIPage, UIUtils}
 private[spark] class HistoryPage(parent: HistoryServer) extends WebUIPage("") {
 
   def render(request: HttpServletRequest): Seq[Node] = {
-    val appRows = parent.appIdToInfo.values.toSeq.sortBy { app => -app.lastUpdated }
-    val appTable = UIUtils.listingTable(appHeader, appRow, appRows)
+    val apps = parent.getApplicationList(0, -1)
+    val appTable = UIUtils.listingTable(appHeader, appRow, apps)
     val content =
       <div class="row-fluid">
         <div class="span12">
-          <ul class="unstyled">
-            <li><strong>Event Log Location: </strong> {parent.baseLogDir}</li>
-          </ul>
           {
-            if (parent.appIdToInfo.size > 0) {
+            if (apps.size > 0) {
               <h4>
-                Showing {parent.appIdToInfo.size}/{parent.getNumApplications}
-                Completed Application{if (parent.getNumApplications > 1) "s" else ""}
+                Showing {apps.size}/{apps.size}
+                Completed Application{if (apps.size > 1) "s" else ""}
               </h4> ++
               appTable
             } else {
@@ -56,26 +53,23 @@ private[spark] class HistoryPage(parent: HistoryServer) extends WebUIPage("") {
     "Completed",
     "Duration",
     "Spark User",
-    "Log Directory",
     "Last Updated")
 
   private def appRow(info: ApplicationHistoryInfo): Seq[Node] = {
-    val appName = if (info.started) info.name else info.logDirPath.getName
-    val uiAddress = parent.getAddress + info.ui.basePath
+    val appName = if (info.started) info.name else info.id
+    val uiAddress = "/history/" + info.id
     val startTime = if (info.started) UIUtils.formatDate(info.startTime) else "Not started"
     val endTime = if (info.completed) UIUtils.formatDate(info.endTime) else "Not completed"
     val difference = if (info.started && info.completed) info.endTime - info.startTime else -1L
     val duration = if (difference > 0) UIUtils.formatDuration(difference) else "---"
     val sparkUser = if (info.started) info.sparkUser else "Unknown user"
-    val logDirectory = info.logDirPath.getName
     val lastUpdated = UIUtils.formatDate(info.lastUpdated)
     <tr>
       <td><a href={uiAddress}>{appName}</a></td>
       <td>{startTime}</td>
       <td>{endTime}</td>
       <td>{duration}</td>
       <td>{sparkUser}</td>
-      <td>{logDirectory}</td>
       <td>{lastUpdated}</td>
     </tr>
   }