[SPARK-27065][CORE] avoid more than one active task set managers for …

…a stage

## What changes were proposed in this pull request?

This is another attempt to fix the more-than-one-active-task-set-managers bug.

apache#17208 is the first attempt. It marks the TSM as zombie before sending a task completion event to DAGScheduler. This is necessary, because when the DAGScheduler gets the task completion event, and it's for the last partition, then the stage is finished. However, if it's a shuffle stage and it has missing map outputs, DAGScheduler will resubmit it(see the [code](https://github.com/apache/spark/blob/v2.4.0/core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala#L1416-L1422)) and create a new TSM for this stage. This leads to more than one active TSM of a stage and fail.

This fix has a hole: Let's say a stage has 10 partitions and 2 task set managers: TSM1(zombie) and TSM2(active). TSM1 has a running task for partition 10 and it completes. TSM2 finishes tasks for partitions 1-9, and thinks he is still active because he hasn't finished partition 10 yet. However, DAGScheduler gets task completion events for all the 10 partitions and thinks the stage is finished. Then the same problem occurs: DAGScheduler may resubmit the stage and cause more than one actice TSM error.

apache#21131 fixed this hole by notifying all the task set managers when a task finishes. For the above case, TSM2 will know that partition 10 is already completed, so he can mark himself as zombie after partitions 1-9 are completed.

However, apache#21131 still has a hole: TSM2 may be created after the task from TSM1 is completed. Then TSM2 can't get notified about the task completion, and leads to the more than one active TSM error.

apache#22806 and apache#23871 are created to fix this hole. However the fix is complicated and there are still ongoing discussions.

This PR proposes a simple fix, which can be easy to backport: mark all existing task set managers as zombie when trying to create a new task set manager.

After this PR, apache#21131 is still necessary, to avoid launching unnecessary tasks and fix [SPARK-25250](https://issues.apache.org/jira/browse/SPARK-25250 ). apache#22806 and apache#23871 are its followups to fix the hole.

## How was this patch tested?

existing tests.

Closes apache#23927 from cloud-fan/scheduler.

Authored-by: Wenchen Fan <[email protected]>
Signed-off-by: Imran Rashid <[email protected]>
(cherry picked from commit cb20fbc)
Signed-off-by: Imran Rashid <[email protected]>

core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala

@@ -207,14 +207,20 @@ private[spark] class TaskSchedulerImpl(
       val stage = taskSet.stageId
       val stageTaskSets =
         taskSetsByStageIdAndAttempt.getOrElseUpdate(stage, new HashMap[Int, TaskSetManager])
-      stageTaskSets(taskSet.stageAttemptId) = manager
-      val conflictingTaskSet = stageTaskSets.exists { case (_, ts) =>
-        ts.taskSet != taskSet && !ts.isZombie
-      }
-      if (conflictingTaskSet) {
-        throw new IllegalStateException(s"more than one active taskSet for stage $stage:" +
-          s" ${stageTaskSets.toSeq.map{_._2.taskSet.id}.mkString(",")}")
+
+      // Mark all the existing TaskSetManagers of this stage as zombie, as we are adding a new one.
+      // This is necessary to handle a corner case. Let's say a stage has 10 partitions and has 2
+      // TaskSetManagers: TSM1(zombie) and TSM2(active). TSM1 has a running task for partition 10
+      // and it completes. TSM2 finishes tasks for partition 1-9, and thinks he is still active
+      // because partition 10 is not completed yet. However, DAGScheduler gets task completion
+      // events for all the 10 partitions and thinks the stage is finished. If it's a shuffle stage
+      // and somehow it has missing map outputs, then DAGScheduler will resubmit it and create a
+      // TSM3 for it. As a stage can't have more than one active task set managers, we must mark
+      // TSM2 as zombie (it actually is).
+      stageTaskSets.foreach { case (_, ts) =>
+        ts.isZombie = true
       }
+      stageTaskSets(taskSet.stageAttemptId) = manager
       schedulableBuilder.addTaskSetManager(manager, manager.taskSet.properties)
 
       if (!isLocal && !hasReceivedTask) {

core/src/test/scala/org/apache/spark/scheduler/TaskSchedulerImplSuite.scala

@@ -201,28 +201,39 @@ class TaskSchedulerImplSuite extends SparkFunSuite with LocalSparkContext with B
     // Even if one of the task sets has not-serializable tasks, the other task set should
     // still be processed without error
     taskScheduler.submitTasks(FakeTask.createTaskSet(1))
-    taskScheduler.submitTasks(taskSet)
+    val taskSet2 = new TaskSet(
+      Array(new NotSerializableFakeTask(1, 0), new NotSerializableFakeTask(0, 1)), 1, 0, 0, null)
+    taskScheduler.submitTasks(taskSet2)
     taskDescriptions = taskScheduler.resourceOffers(multiCoreWorkerOffers).flatten
     assert(taskDescriptions.map(_.executorId) === Seq("executor0"))
   }
 
-  test("refuse to schedule concurrent attempts for the same stage (SPARK-8103)") {
+  test("concurrent attempts for the same stage only have one active taskset") {
     val taskScheduler = setupScheduler()
+    def isTasksetZombie(taskset: TaskSet): Boolean = {
+      taskScheduler.taskSetManagerForAttempt(taskset.stageId, taskset.stageAttemptId).get.isZombie
+    }
+
     val attempt1 = FakeTask.createTaskSet(1, 0)
-    val attempt2 = FakeTask.createTaskSet(1, 1)
     taskScheduler.submitTasks(attempt1)
-    intercept[IllegalStateException] { taskScheduler.submitTasks(attempt2) }
+    // The first submitted taskset is active
+    assert(!isTasksetZombie(attempt1))
 
-    // OK to submit multiple if previous attempts are all zombie
-    taskScheduler.taskSetManagerForAttempt(attempt1.stageId, attempt1.stageAttemptId)
-      .get.isZombie = true
+    val attempt2 = FakeTask.createTaskSet(1, 1)
     taskScheduler.submitTasks(attempt2)
+    // The first submitted taskset is zombie now
+    assert(isTasksetZombie(attempt1))
+    // The newly submitted taskset is active
+    assert(!isTasksetZombie(attempt2))
+
     val attempt3 = FakeTask.createTaskSet(1, 2)
-    intercept[IllegalStateException] { taskScheduler.submitTasks(attempt3) }
-    taskScheduler.taskSetManagerForAttempt(attempt2.stageId, attempt2.stageAttemptId)
-      .get.isZombie = true
     taskScheduler.submitTasks(attempt3)
-    assert(!failedTaskSet)
+    // The first submitted taskset remains zombie
+    assert(isTasksetZombie(attempt1))
+    // The second submitted taskset is zombie now
+    assert(isTasksetZombie(attempt2))
+    // The newly submitted taskset is active
+    assert(!isTasksetZombie(attempt3))
   }
 
   test("don't schedule more tasks after a taskset is zombie") {