ShuffleExchangeExec

  private lazy val writeMetrics =SQLShuffleWriteMetricsReporter.createShuffleWriteMetrics(sparkContext)private[sql] lazy val readMetrics =SQLShuffleReadMetricsReporter.createShuffleReadMetrics(sparkContext)

用在了兩個地方，承接的是前后兩個stage 的metrics

  /*** A [[ShuffleDependency]] that will partition rows of its child based on* the partitioning scheme defined in `newPartitioning`. Those partitions of* the returned ShuffleDependency will be the input of shuffle.*/@transientlazy val shuffleDependency : ShuffleDependency[Int, InternalRow, InternalRow] = {val dep = ShuffleExchangeExec.prepareShuffleDependency(inputRDD,child.output,outputPartitioning,serializer,writeMetrics)metrics("numPartitions").set(dep.partitioner.numPartitions)val executionId = sparkContext.getLocalProperty(SQLExecution.EXECUTION_ID_KEY)SQLMetrics.postDriverMetricUpdates(sparkContext, executionId, metrics("numPartitions") :: Nil)dep}

  protected override def doExecute(): RDD[InternalRow] = {// Returns the same ShuffleRowRDD if this plan is used by multiple plans.if (cachedShuffleRDD == null) {cachedShuffleRDD = new ShuffledRowRDD(shuffleDependency, readMetrics)}cachedShuffleRDD}

一般情況是，兩個metrics 相同。 write 在前，read 在后

如果下個shuffle read task 沒有完成或者失敗，就會出現read 比write 少的情況。

broadcast

  /** Remove all blocks belonging to the given broadcast. */def removeBroadcast(broadcastId: Long, removeFromMaster: Boolean, blocking: Boolean): Unit = {val future = driverEndpoint.askSync[Future[Seq[Int]]](RemoveBroadcast(broadcastId, removeFromMaster))future.failed.foreach(e =>logWarning(s"Failed to remove broadcast $broadcastId" +s" with removeFromMaster = $removeFromMaster - ${e.getMessage}", e))(ThreadUtils.sameThread)if (blocking) {// the underlying Futures will timeout anyway, so it's safe to use infinite timeout hereRpcUtils.INFINITE_TIMEOUT.awaitResult(future)}}