Github user witgo commented on a diff in the pull request: https://github.com/apache/spark/pull/12113#discussion_r58641966 --- Diff: core/src/main/scala/org/apache/spark/MapOutputTracker.scala --- @@ -296,10 +290,89 @@ private[spark] class MapOutputTrackerMaster(conf: SparkConf) protected val mapStatuses = new ConcurrentHashMap[Int, Array[MapStatus]]().asScala private val cachedSerializedStatuses = new ConcurrentHashMap[Int, Array[Byte]]().asScala + private val maxRpcMessageSize = RpcUtils.maxMessageSizeBytes(conf) + + // Kept in sync with cachedSerializedStatuses explicitly + // This is required so that the Broadcast variable remains in scope until we remove + // the shuffleId explicitly or implicitly. + private val cachedSerializedBroadcast = new HashMap[Int, Broadcast[Array[Byte]]]() + + // This is to prevent multiple serializations of the same shuffle - which happens when + // there is a request storm when shuffle start. + private val shuffleIdLocks = new ConcurrentHashMap[Int, AnyRef]() + + // requests for map output statuses + private val mapOutputRequests = new LinkedBlockingQueue[GetMapOutputMessage] + + // Thread pool used for handling map output status requests. This is a separate thread pool + // to ensure we don't block the normal dispatcher threads. + private val threadpool: ThreadPoolExecutor = { + val numThreads = conf.getInt("spark.shuffle.mapOutput.dispatcher.numThreads", 8) + val pool = ThreadUtils.newDaemonFixedThreadPool(numThreads, "map-output-dispatcher") + for (i <- 0 until numThreads) { + pool.execute(new MessageLoop) + } + pool + } + + def post(message: GetMapOutputMessage): Unit = { + mapOutputRequests.offer(message) + } + + /** Message loop used for dispatching messages. */ + private class MessageLoop extends Runnable { + override def run(): Unit = { + try { + while (true) { + try { + val data = mapOutputRequests.take() + if (data == PoisonPill) { + // Put PoisonPill back so that other MessageLoops can see it. + mapOutputRequests.offer(PoisonPill) + return + } + val context = data.context + val shuffleId = data.shuffleId + val hostPort = context.senderAddress.hostPort + logDebug("Handling request to send map output locations for shuffle " + shuffleId + + " to " + hostPort) + val mapOutputStatuses = getSerializedMapOutputStatuses(shuffleId) --- End diff -- > Are you saying 7 additional seconds on top of the serialization? I mean, calling `getSerializedMapOutputStatuses` takes seven seconds ,but this is not accurate, is estimated with the production logs. > What is your timeout set at? By default, no change. > How long is it taking for the entire serialization (even without this change)? The master branch throws ``` org.apache.spark.shuffle.FetchFailedException: java.lang.OutOfMemoryError: Direct buffer memory ```
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