diff --git a/core/src/main/scala/org/apache/spark/TaskEndReason.scala b/core/src/main/scala/org/apache/spark/TaskEndReason.scala
index 7745387dbceba..35985c20ee7c3 100644
--- a/core/src/main/scala/org/apache/spark/TaskEndReason.scala
+++ b/core/src/main/scala/org/apache/spark/TaskEndReason.scala
@@ -140,7 +140,8 @@ case class ExceptionFailure(
       e: Throwable,
       accumUpdates: Seq[AccumulableInfo],
       preserveCause: Boolean) {
-    this(e.getClass.getName, e.getMessage, e.getStackTrace, Utils.exceptionString(e),
+    this(e.getClass.getName, e.getMessage, e.getStackTrace,
+      if (Utils.dumpStackTrace(e)) Utils.exceptionString(e) else null,
       if (preserveCause) Some(new ThrowableSerializationWrapper(e)) else None, accumUpdates)
   }
 
diff --git a/core/src/main/scala/org/apache/spark/executor/Executor.scala b/core/src/main/scala/org/apache/spark/executor/Executor.scala
index 85fda2a736d46..7782304c98e77 100644
--- a/core/src/main/scala/org/apache/spark/executor/Executor.scala
+++ b/core/src/main/scala/org/apache/spark/executor/Executor.scala
@@ -453,7 +453,14 @@ private[spark] class Executor(
           // Attempt to exit cleanly by informing the driver of our failure.
           // If anything goes wrong (or this was a fatal exception), we will delegate to
           // the default uncaught exception handler, which will terminate the Executor.
-          logError(s"Exception in $taskName (TID $taskId)", t)
+          val errorMessage = s"Exception in $taskName (TID $taskId) (SW: t=${t.getClass})"
+          if (Utils.dumpStackTrace(t)) {
+            logError(errorMessage, t)
+          } else if (isTraceEnabled) {
+            logWarning(errorMessage, t)
+          } else {
+            logWarning(errorMessage + ": " + t.toString)
+          }
 
           // Collect latest accumulator values to report back to the driver
           val accums: Seq[AccumulatorV2[_, _]] =
diff --git a/core/src/main/scala/org/apache/spark/memory/ExecutionMemoryPool.scala b/core/src/main/scala/org/apache/spark/memory/ExecutionMemoryPool.scala
index ab783554f0b2c..cf91fcf2faaf9 100644
--- a/core/src/main/scala/org/apache/spark/memory/ExecutionMemoryPool.scala
+++ b/core/src/main/scala/org/apache/spark/memory/ExecutionMemoryPool.scala
@@ -56,7 +56,12 @@ private[memory] class ExecutionMemoryPool(
   private val memoryForTask = new mutable.HashMap[Long, Long]()
 
   override def memoryUsed: Long = lock.synchronized {
-    return memoryForTask.values.sum
+    var sum = 0L
+    val iter = memoryForTask.valuesIterator
+    while (iter.hasNext) {
+      sum += iter.next()
+    }
+    return sum
   }
 
   /**
diff --git a/core/src/main/scala/org/apache/spark/memory/StorageMemoryPool.scala b/core/src/main/scala/org/apache/spark/memory/StorageMemoryPool.scala
index 4c6b639015a90..e9886386373c0 100644
--- a/core/src/main/scala/org/apache/spark/memory/StorageMemoryPool.scala
+++ b/core/src/main/scala/org/apache/spark/memory/StorageMemoryPool.scala
@@ -44,7 +44,7 @@ private[memory] class StorageMemoryPool(
   private[this] var _memoryUsed: Long = 0L
 
   override def memoryUsed: Long = lock.synchronized {
-    _memoryUsed
+    return _memoryUsed
   }
 
   private var _memoryStore: MemoryStore = _
diff --git a/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala b/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala
index b03cfe4f0dc49..eb30d4866a118 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala
@@ -94,7 +94,7 @@ private[spark] class TaskSchedulerImpl(
   val nextTaskId = new AtomicLong(0)
 
   // IDs of the tasks running on each executor
-  private val executorIdToRunningTaskIds = new HashMap[String, HashSet[Long]]
+  protected val executorIdToRunningTaskIds = new HashMap[String, HashSet[Long]]
 
   def runningTasksByExecutors: Map[String, Int] = synchronized {
     executorIdToRunningTaskIds.toMap.mapValues(_.size)
@@ -169,10 +169,8 @@ private[spark] class TaskSchedulerImpl(
     waitBackendReady()
   }
 
-  override def submitTasks(taskSet: TaskSet) {
-    val tasks = taskSet.tasks
-    logInfo("Adding task set " + taskSet.id + " with " + tasks.length + " tasks")
-    this.synchronized {
+  protected def getTaskSetManagerForSubmit(taskSet: TaskSet): TaskSetManager = {
+    {
       val manager = createTaskSetManager(taskSet, maxTaskFailures)
       val stage = taskSet.stageId
       val stageTaskSets =
@@ -185,6 +183,15 @@ private[spark] class TaskSchedulerImpl(
         throw new IllegalStateException(s"more than one active taskSet for stage $stage:" +
           s" ${stageTaskSets.toSeq.map{_._2.taskSet.id}.mkString(",")}")
       }
+      manager
+    }
+  }
+
+  override def submitTasks(taskSet: TaskSet) {
+    val tasks = taskSet.tasks
+    logInfo("Adding task set " + taskSet.id + " with " + tasks.length + " tasks")
+    this.synchronized {
+      val manager = getTaskSetManagerForSubmit(taskSet)
       schedulableBuilder.addTaskSetManager(manager, manager.taskSet.properties)
 
       if (!isLocal && !hasReceivedTask) {
@@ -249,7 +256,7 @@ private[spark] class TaskSchedulerImpl(
       s" ${manager.parent.name}")
   }
 
-  private def resourceOfferSingleTaskSet(
+  protected def resourceOfferSingleTaskSet(
       taskSet: TaskSetManager,
       maxLocality: TaskLocality,
       shuffledOffers: Seq[WorkerOffer],
@@ -346,18 +353,30 @@ private[spark] class TaskSchedulerImpl(
     return tasks
   }
 
+  protected[scheduler] def getTaskSetManager(tid: Long): Option[TaskSetManager] =
+    taskIdToTaskSetManager.get(tid)
+
+  protected def getExecutorAndManager(tid: Long): Option[(() => String, TaskSetManager)] = {
+    taskIdToTaskSetManager.get(tid) match {
+      case Some(taskSet) =>
+        val getExecId = () => taskIdToExecutorId.getOrElse(tid, throw new IllegalStateException(
+          "taskIdToTaskSetManager.contains(tid) <=> taskIdToExecutorId.contains(tid)"))
+        Some(getExecId -> taskSet)
+      case None => None
+    }
+  }
+
   def statusUpdate(tid: Long, state: TaskState, serializedData: ByteBuffer) {
     var failedExecutor: Option[String] = None
     var reason: Option[ExecutorLossReason] = None
     synchronized {
       try {
-        taskIdToTaskSetManager.get(tid) match {
-          case Some(taskSet) =>
+        getExecutorAndManager(tid) match {
+          case Some((getExecId, taskSet)) =>
             if (state == TaskState.LOST) {
               // TaskState.LOST is only used by the deprecated Mesos fine-grained scheduling mode,
               // where each executor corresponds to a single task, so mark the executor as failed.
-              val execId = taskIdToExecutorId.getOrElse(tid, throw new IllegalStateException(
-                "taskIdToTaskSetManager.contains(tid) <=> taskIdToExecutorId.contains(tid)"))
+              val execId = getExecId()
               if (executorIdToRunningTaskIds.contains(execId)) {
                 reason = Some(
                   SlaveLost(s"Task $tid was lost, so marking the executor as lost as well."))
@@ -406,7 +425,7 @@ private[spark] class TaskSchedulerImpl(
     val accumUpdatesWithTaskIds: Array[(Long, Int, Int, Seq[AccumulableInfo])] = synchronized {
       accumUpdates.flatMap { case (id, updates) =>
         val accInfos = updates.map(acc => acc.toInfo(Some(acc.value), None))
-        taskIdToTaskSetManager.get(id).map { taskSetMgr =>
+        getTaskSetManager(id).map { taskSetMgr =>
           (id, taskSetMgr.stageId, taskSetMgr.taskSet.stageAttemptId, accInfos)
         }
       }
@@ -534,7 +553,7 @@ private[spark] class TaskSchedulerImpl(
   /**
    * Cleans up the TaskScheduler's state for tracking the given task.
    */
-  private def cleanupTaskState(tid: Long): Unit = {
+  protected def cleanupTaskState(tid: Long): Unit = {
     taskIdToTaskSetManager.remove(tid)
     taskIdToExecutorId.remove(tid).foreach { executorId =>
       executorIdToRunningTaskIds.get(executorId).foreach { _.remove(tid) }
diff --git a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
index 26b4a40d05dd6..7707e446659a7 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
@@ -267,7 +267,7 @@ class CoarseGrainedSchedulerBackend(scheduler: TaskSchedulerImpl, val rpcEnv: Rp
 
     protected def checkTaskSizeLimit(task: TaskDescription, taskSize: Int): Boolean = {
       if (taskSize > maxRpcMessageSize) {
-        scheduler.taskIdToTaskSetManager.get(task.taskId).foreach { taskSetMgr =>
+        scheduler.getTaskSetManager(task.taskId).foreach { taskSetMgr =>
           try {
             var msg = "Serialized task %s:%d was %d bytes, which exceeds max allowed: " +
                 "spark.rpc.message.maxSize (%d bytes). Consider increasing " +
diff --git a/core/src/main/scala/org/apache/spark/util/Utils.scala b/core/src/main/scala/org/apache/spark/util/Utils.scala
index 308bbbc734ab9..3edbdb2f02546 100644
--- a/core/src/main/scala/org/apache/spark/util/Utils.scala
+++ b/core/src/main/scala/org/apache/spark/util/Utils.scala
@@ -2159,6 +2159,28 @@ private[spark] object Utils extends Logging {
     }
   }
 
+  @tailrec
+  private def getSQLException(t: Throwable): Option[java.sql.SQLException] = t match {
+    case null => None
+    case se: java.sql.SQLException => Some(se)
+    case _ => getSQLException(t.getCause)
+  }
+
+  /**
+   * Return true if stack trace for the exception should be dumped and false otherwise.
+   */
+  def dumpStackTrace(e: Throwable): Boolean = {
+    // skip stack traces for SQLExceptions for syntax error, constraint violation etc
+    getSQLException(e) match {
+      case Some(se) =>
+        val state = se.getSQLState
+        !state.startsWith("23") && // constraint violations etc
+            !state.startsWith("42") && // syntax, auth errors
+            !state.startsWith("X0Z02") // conflict exception
+      case None => false
+    }
+  }
+
   private implicit class Lock(lock: LockInfo) {
     def lockString: String = {
       lock match {