Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/4066#discussion_r24043135
--- Diff:
core/src/main/scala/org/apache/spark/scheduler/OutputCommitCoordinator.scala ---
@@ -0,0 +1,199 @@
+/*
+ * 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
+
+import scala.collection.mutable
+
+import akka.actor.{ActorRef, Actor}
+
+import org.apache.spark._
+import org.apache.spark.util.{AkkaUtils, ActorLogReceive}
+
+private sealed trait OutputCommitCoordinationMessage extends Serializable
+
+private case class StageStarted(stage: Int) extends
OutputCommitCoordinationMessage
+private case class StageEnded(stage: Int) extends
OutputCommitCoordinationMessage
+private case object StopCoordinator extends OutputCommitCoordinationMessage
+
+private case class AskPermissionToCommitOutput(
+ stage: Int,
+ task: Long,
+ taskAttempt: Long)
+ extends OutputCommitCoordinationMessage
+
+private case class TaskCompleted(
+ stage: Int,
+ task: Long,
+ attempt: Long,
+ reason: TaskEndReason)
+ extends OutputCommitCoordinationMessage
+
+/**
+ * Authority that decides whether tasks can commit output to HDFS.
+ *
+ * This lives on the driver, but the actor allows the tasks that commit to
Hadoop to invoke it.
+ *
+ * This class was introduced in SPARK-4879; see that JIRA issue (and the
associated pull requests)
+ * for an extensive design discussion.
+ */
+private[spark] class OutputCommitCoordinator(conf: SparkConf) extends
Logging {
+
+ // Initialized by SparkEnv
+ var coordinatorActor: Option[ActorRef] = None
+ private val timeout = AkkaUtils.askTimeout(conf)
+ private val maxAttempts = AkkaUtils.numRetries(conf)
+ private val retryInterval = AkkaUtils.retryWaitMs(conf)
+
+ private type StageId = Int
+ private type TaskId = Long
+ private type TaskAttemptId = Long
+ private type CommittersByStageMap = mutable.Map[StageId,
mutable.Map[TaskId, TaskAttemptId]]
+
+ private val authorizedCommittersByStage: CommittersByStageMap =
mutable.Map()
+
+ /**
+ * Called by tasks to ask whether they can commit their output to HDFS.
+ *
+ * If a task attempt has been authorized to commit, then all other
attempts to commit the same
+ * task will be denied. If the authorized task attempt fails (e.g. due
to its executor being
+ * lost), then a subsequent task attempt may be authorized to commit its
output.
+ *
+ * @param stage the stage number
+ * @param task the task number
+ * @param attempt a unique identifier for this task attempt
+ * @return true if this task is authorized to commit, false otherwise
+ */
+ def canCommit(
+ stage: StageId,
+ task: TaskId,
+ attempt: TaskAttemptId): Boolean = {
+ askActor(AskPermissionToCommitOutput(stage, task, attempt))
+ }
+
+ // Called by DAGScheduler
+ private[scheduler] def stageStart(stage: StageId): Unit = {
+ sendToActor(StageStarted(stage))
+ }
+
+ // Called by DAGScheduler
+ private[scheduler] def stageEnd(stage: StageId): Unit = {
+ sendToActor(StageEnded(stage))
+ }
+
+ // Called by DAGScheduler
+ private[scheduler] def taskCompleted(
+ stage: StageId,
+ task: TaskId,
+ attempt: TaskAttemptId,
+ reason: TaskEndReason): Unit = {
+ sendToActor(TaskCompleted(stage, task, attempt, reason))
+ }
+
+ def stop(): Unit = {
+ sendToActor(StopCoordinator)
+ coordinatorActor = None
+ authorizedCommittersByStage.foreach(_._2.clear)
+ authorizedCommittersByStage.clear
+ }
+
+ private def handleStageStart(stage: StageId): Unit = {
+ authorizedCommittersByStage(stage) = mutable.HashMap[TaskId,
TaskAttemptId]()
+ }
+
+ private def handleStageEnd(stage: StageId): Unit = {
+ authorizedCommittersByStage.remove(stage)
+ }
+
+ private def handleAskPermissionToCommit(
+ stage: StageId,
+ task: TaskId,
+ attempt: TaskAttemptId): Boolean = {
+ authorizedCommittersByStage.get(stage) match {
+ case Some(authorizedCommitters) =>
+ authorizedCommitters.get(task) match {
+ case Some(existingCommitter) =>
+ logDebug(s"Denying $attempt to commit for stage=$stage,
task=$task; " +
+ s"existingCommitter = $existingCommitter")
+ false
+ case None =>
+ logDebug(s"Authorizing $attempt to commit for stage=$stage,
task=$task")
+ authorizedCommitters(task) = attempt
+ true
+ }
+ case None =>
+ logDebug(s"Stage $stage has completed, so not allowing task
attempt $attempt to commit")
+ return false
+ }
+ }
+
+ private def handleTaskCompletion(
+ stage: StageId,
+ task: TaskId,
+ attempt: TaskAttemptId,
+ reason: TaskEndReason): Unit = {
+ val authorizedCommitters =
authorizedCommittersByStage.getOrElse(stage, {
+ logDebug(s"Ignoring task completion for completed stage")
+ return
+ })
+ reason match {
+ case Success =>
+ // The task output has been committed successfully
+ case TaskCommitDenied(jobID, splitID, attemptID) =>
+ logInfo(s"Task was denied committing, stage: $stage, taskId:
$task, attempt: $attempt")
+ case otherReason =>
+ logDebug(s"Authorized committer $attempt (stage=$stage,
task=$task) failed;" +
+ s" clearing lock")
+ authorizedCommitters.remove(task)
+ }
+ }
+
+ private def sendToActor(msg: OutputCommitCoordinationMessage): Unit = {
+ coordinatorActor.foreach(_ ! msg)
+ }
+
+ private def askActor(msg: OutputCommitCoordinationMessage): Boolean = {
+ coordinatorActor match {
--- End diff --
It was this way before, but I found it to be a little dense.
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