[GitHub] [spark] dhruve commented on a change in pull request #24704: [SPARK-20286][core] Improve logic for timing out executors in dynamic allocation.

[GitBox <gi...@apache.org>]

dhruve commented on a change in pull request #24704: [SPARK-20286][core] Improve logic for timing out executors in dynamic allocation.
URL: https://github.com/apache/spark/pull/24704#discussion_r289454846
 
 

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 File path: core/src/main/scala/org/apache/spark/scheduler/dynalloc/ExecutorMonitor.scala
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+/*
+ * 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.scheduler.dynalloc
+
+import java.util.concurrent.{ConcurrentHashMap, TimeUnit}
+import java.util.concurrent.atomic.AtomicLong
+
+import scala.collection.JavaConverters._
+import scala.collection.mutable
+
+import org.apache.spark._
+import org.apache.spark.internal.Logging
+import org.apache.spark.internal.config._
+import org.apache.spark.scheduler._
+import org.apache.spark.storage.RDDBlockId
+import org.apache.spark.util.Clock
+
+/**
+ * A monitor for executor activity, used by ExecutorAllocationManager to detect idle executors.
+ */
+private[spark] class ExecutorMonitor(
+    conf: SparkConf,
+    client: ExecutorAllocationClient,
+    clock: Clock) extends SparkListener with Logging {
+
+  private val idleTimeoutMs = TimeUnit.SECONDS.toMillis(
+    conf.get(DYN_ALLOCATION_EXECUTOR_IDLE_TIMEOUT))
+  private val storageTimeoutMs = TimeUnit.SECONDS.toMillis(
+    conf.get(DYN_ALLOCATION_CACHED_EXECUTOR_IDLE_TIMEOUT))
+  private val fetchFromShuffleSvcEnabled = conf.get(SHUFFLE_SERVICE_ENABLED) &&
+    conf.get(SHUFFLE_SERVICE_FETCH_RDD_ENABLED)
+
+  private val executors = new ConcurrentHashMap[String, Tracker]()
+
+  // The following fields are an optimization to avoid having to scan all executors on every EAM
+  // schedule interval to find out which ones are timed out. They keep track of when the next
+  // executor timeout is expected to happen, and the current list of timed out executors. There's
+  // also a flag that forces the EAM task to recompute the timed out executors, in case some event
+  // arrives on the listener bus that may cause the current list of timed out executors to change.
+  //
+  // There's also per-executor state used for this purpose, so that recomputations can be triggered
+  // only when really necessary.
+  //
+  // Note that this isn't meant to, and cannot, always make the right decision about which executors
+  // are indeed timed out. For example, the EAM thread may detect a timed out executor while a new
+  // "task start" event has just been posted to the listener bus and hasn't yet been delivered to
+  // this listener. There are safeguards in other parts of the code that would prevent that executor
+  // from being removed.
+  private var nextTimeout = new AtomicLong(Long.MaxValue)
+  private var timedOutExecs = Seq.empty[String]
+
+  def reset(): Unit = {
+    executors.clear()
+    nextTimeout.set(Long.MaxValue)
+    timedOutExecs = Nil
+  }
+
+  /**
+   * Returns the list of executors that are currently considered to be timed out.
+   * Should only be called from the EAM thread.
+   */
+  def timedOutExecutors(): Seq[String] = {
+    val now = clock.getTimeMillis()
+    if (now >= nextTimeout.get()) {
+      // Temporarily set the next timeout at Long.MaxValue. This ensures that after
+      // scanning all executors below, we know when the next timeout for non-timed out
+      // executors is (whether that update came from the scan, or from a new event
+      // arriving in a different thread).
+      nextTimeout.set(Long.MaxValue)
+
+      var newNextTimeout = Long.MaxValue
+      timedOutExecs = executors.asScala
+        .filter { case (_, exec) => !exec.pendingRemoval }
+        .filter { case (_, exec) =>
+          val deadline = exec.timeoutAt
+          if (deadline > now) {
+            newNextTimeout = math.min(newNextTimeout, deadline)
+            exec.timedOut = false
+            false
+          } else {
+            exec.timedOut = true
+            true
+          }
+        }
+        .keys
+        .toSeq
+      updateNextTimeout(newNextTimeout)
+    }
+    timedOutExecs
+  }
+
+  /**
+   * Mark the given executors as pending to be removed. Should only be called in the EAM thread.
+   */
+  def executorsKilled(ids: Seq[String]): Unit = {
+    ids.foreach { id =>
+      val tracker = executors.get(id)
+      if (tracker != null) {
+        tracker.pendingRemoval = true
+      }
+    }
+
+    // Recompute timed out executors in the next EAM callback, since this call invalidates
+    // the current list.
+    nextTimeout.set(Long.MinValue)
+  }
+
+  def executorCount: Int = executors.size()
+
+  def pendingRemovalCount: Int = executors.asScala.count { case (_, exec) => exec.pendingRemoval }
+
+  override def onTaskStart(event: SparkListenerTaskStart): Unit = {
+    val executorId = event.taskInfo.executorId
+    // Guard against a late arriving task start event (SPARK-26927).
+    if (client.isExecutorActive(executorId)) {
+      val exec = ensureExecutorIsTracked(executorId)
+      exec.updateRunningTasks(1)
+    }
+  }
+
+  override def onTaskEnd(event: SparkListenerTaskEnd): Unit = {
+    val executorId = event.taskInfo.executorId
+    val exec = executors.get(executorId)
+    if (exec != null) {
+      exec.updateRunningTasks(-1)
+    }
+  }
+
+  override def onExecutorAdded(event: SparkListenerExecutorAdded): Unit = {
+    val exec = ensureExecutorIsTracked(event.executorId)
+    exec.updateRunningTasks(0)
+    logInfo(s"New executor ${event.executorId} has registered (new total is ${executors.size()})")
+  }
+
+  override def onExecutorRemoved(event: SparkListenerExecutorRemoved): Unit = {
+    val removed = executors.remove(event.executorId)
+    if (removed != null) {
+      logInfo(s"Executor ${event.executorId} removed (new total is ${executors.size()})")
+      if (!removed.pendingRemoval) {
+        nextTimeout.set(Long.MinValue)
+      }
+    }
+  }
+
+  override def onBlockUpdated(event: SparkListenerBlockUpdated): Unit = {
+    if (!event.blockUpdatedInfo.blockId.isInstanceOf[RDDBlockId]) {
+      return
+    }
+
+    val exec = ensureExecutorIsTracked(event.blockUpdatedInfo.blockManagerId.executorId)
+    val storageLevel = event.blockUpdatedInfo.storageLevel
+    val blockId = event.blockUpdatedInfo.blockId.asInstanceOf[RDDBlockId]
+
+    // SPARK-27677. When a block can be fetched from the external shuffle service, the executor can
+    // be removed without hurting the application too much, since the cached data is still
+    // available. So don't count blocks that can be served by the external service.
+    if (storageLevel.isValid && (!fetchFromShuffleSvcEnabled || !storageLevel.useDisk)) {
+      val hadCachedBlocks = exec.cachedBlocks.nonEmpty
+
+      val blocks = exec.cachedBlocks.getOrElseUpdate(blockId.rddId,
+        new mutable.BitSet(blockId.splitIndex))
+      blocks += blockId.splitIndex
+
+      if (!hadCachedBlocks) {
+        exec.updateTimeout()
+      }
+    } else {
+      exec.cachedBlocks.get(blockId.rddId).foreach { blocks =>
+        blocks -= blockId.splitIndex
+        if (blocks.isEmpty) {
+          exec.cachedBlocks -= blockId.rddId
+          if (exec.cachedBlocks.isEmpty) {
+            exec.updateTimeout()
+          }
+        }
+      }
+    }
+  }
+
+  override def onUnpersistRDD(event: SparkListenerUnpersistRDD): Unit = {
+    executors.values().asScala.foreach { exec =>
+      exec.cachedBlocks -= event.rddId
+      if (exec.cachedBlocks.isEmpty) {
+        exec.updateTimeout()
+      }
+    }
+  }
+
+  // Visible for testing.
+  private[dynalloc] def isExecutorIdle(id: String): Boolean = {
+    Option(executors.get(id)).map(_.isIdle).getOrElse(throw new NoSuchElementException(id))
+  }
+
+  // Visible for testing
+  private[dynalloc] def timedOutExecutors(when: Long): Seq[String] = {
+    executors.asScala.flatMap { case (id, tracker) =>
+      if (tracker.timeoutAt <= when) Some(id) else None
+    }.toSeq
+  }
+
+  // Visible for testing
+  def executorsPendingToRemove(): Set[String] = {
+    executors.asScala.filter { case (_, exec) => exec.pendingRemoval }.keys.toSet
+  }
+
+  /**
+   * This method should be used when updating executor state. It guards against a race condition in
+   * which the `SparkListenerTaskStart` event is posted before the `SparkListenerBlockManagerAdded`
+   * event, which is possible because these events are posted in different threads. (see SPARK-4951)
+   */
+  private def ensureExecutorIsTracked(id: String): Tracker = {
+    executors.computeIfAbsent(id, _ => new Tracker())
+  }
+
+  private def updateNextTimeout(newValue: Long): Unit = {
+    while (true) {
+      val current = nextTimeout.get()
+      if (newValue >= current || nextTimeout.compareAndSet(current, newValue)) {
+        return
+      }
+    }
+  }
+
+  private class Tracker {
+    @volatile var timeoutAt: Long = Long.MaxValue
+
+    // Tracks whether this executor is thought to be timed out. It's used to detect when the list
+    // of timed out executors needs to be updated due to the executor's state changing.
+    @volatile var timedOut: Boolean = false
+
+    var pendingRemoval: Boolean = false
+
+    private var idleStart: Long = -1
+    private var runningTasks: Int = 0
+
+    // Maps RDD IDs to the partition IDs stored in the executor.
+    // This should only be used in the event thread.
+    val cachedBlocks = new mutable.HashMap[Int, mutable.BitSet]()
+
+    // For testing.
+    def isIdle: Boolean = idleStart >= 0
+
+    def updateRunningTasks(delta: Int): Unit = {
+      runningTasks = math.max(0, runningTasks + delta)
+      idleStart = if (runningTasks == 0) clock.getTimeMillis() else -1L
+      updateTimeout()
+    }
+
+    def updateTimeout(): Unit = {
+      val oldDeadline = timeoutAt
+      val newDeadline = if (idleStart >= 0) {
 
 Review comment:
   `idleStart` seems to be redundant. We could just use `runningTasks == 0`

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