[SPARK-31253][SQL][FOLLOWUP] Add metrics to AQE shuffle reader

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This is a followup of https://github.com/apache/spark/pull/28022, to address three issues:
1. Add an assert in `CustomShuffleReaderExec` to make sure the partitions specs are all `PartialMapperPartitionSpec` or none.
2. Do not use `lazy val` for `partitionDataSizeMetrics` and `skewedPartitionMetrics`, as they will be merged into `metrics`, and `lazy val` will be serialized.
3. mark `metrics` as `transient`, as it's only used at driver-side
4. move `FileUtils.byteCountToDisplaySize` to `logDebug`, to save some calculation if log level is above debug.

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followup improvement

### Does this PR introduce any user-facing change?
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no

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existing tests

Closes #28103 from cloud-fan/ui.

Authored-by: Wenchen Fan <wenchen@databricks.com>
Signed-off-by: gatorsmile <gatorsmile@gmail.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/CustomShuffleReaderExec.scala

@@ -36,6 +36,11 @@ import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}
 case class CustomShuffleReaderExec private(
     child: SparkPlan,
     partitionSpecs: Seq[ShufflePartitionSpec]) extends UnaryExecNode {
+  // If this reader is to read shuffle files locally, then all partition specs should be
+  // `PartialMapperPartitionSpec`.
+  if (partitionSpecs.exists(_.isInstanceOf[PartialMapperPartitionSpec])) {
+    assert(partitionSpecs.forall(_.isInstanceOf[PartialMapperPartitionSpec]))
+  }
 
   override def output: Seq[Attribute] = child.output
   override lazy val outputPartitioning: Partitioning = {
@@ -76,29 +81,21 @@ case class CustomShuffleReaderExec private(
     Iterator(desc)
   }
 
-  def hasCoalescedPartition: Boolean = {
+  def hasCoalescedPartition: Boolean =
     partitionSpecs.exists(_.isInstanceOf[CoalescedPartitionSpec])
-  }
 
-  def hasSkewedPartition: Boolean = {
+  def hasSkewedPartition: Boolean =
     partitionSpecs.exists(_.isInstanceOf[PartialReducerPartitionSpec])
-  }
 
-  def isLocalReader: Boolean = {
-    if (partitionSpecs.exists(_.isInstanceOf[PartialMapperPartitionSpec])) {
-      assert(partitionSpecs.forall(_.isInstanceOf[PartialMapperPartitionSpec]))
-      true
-    } else {
-      false
-    }
-  }
+  def isLocalReader: Boolean =
+    partitionSpecs.exists(_.isInstanceOf[PartialMapperPartitionSpec])
 
   private def shuffleStage = child match {
     case stage: ShuffleQueryStageExec => Some(stage)
     case _ => None
   }
 
-  private lazy val partitionDataSizeMetrics = {
+  private def partitionDataSizeMetrics = {
     val maxSize = SQLMetrics.createSizeMetric(sparkContext, "maximum partition data size")
     val minSize = SQLMetrics.createSizeMetric(sparkContext, "minimum partition data size")
     val avgSize = SQLMetrics.createSizeMetric(sparkContext, "average partition data size")
@@ -118,7 +115,7 @@ case class CustomShuffleReaderExec private(
       "avgPartitionDataSize" -> avgSize)
   }
 
-  private lazy val skewedPartitionMetrics = {
+  private def skewedPartitionMetrics = {
     val metrics = SQLMetrics.createMetric(sparkContext, "number of skewed partitions")
     val numSkewedPartitions = partitionSpecs.collect {
       case p: PartialReducerPartitionSpec => p.reducerIndex
@@ -127,7 +124,7 @@ case class CustomShuffleReaderExec private(
     Map("numSkewedPartitions" -> metrics)
   }
 
-  override lazy val metrics: Map[String, SQLMetric] = {
+  @transient override lazy val metrics: Map[String, SQLMetric] = {
     if (shuffleStage.isDefined) {
       val numPartitions = SQLMetrics.createMetric(sparkContext, "number of partitions")
       numPartitions.set(partitionSpecs.length)

sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/OptimizeSkewedJoin.scala

@@ -186,11 +186,13 @@ case class OptimizeSkewedJoin(conf: SQLConf) extends Rule[SparkPlan] {
       var numSkewedLeft = 0
       var numSkewedRight = 0
       for (partitionIndex <- 0 until numPartitions) {
-        val isLeftSkew = isSkewed(leftActualSizes(partitionIndex), leftMedSize) && canSplitLeft
+        val leftActualSize = leftActualSizes(partitionIndex)
+        val isLeftSkew = isSkewed(leftActualSize, leftMedSize) && canSplitLeft
         val leftPartSpec = left.partitionsWithSizes(partitionIndex)._1
         val isLeftCoalesced = leftPartSpec.startReducerIndex + 1 < leftPartSpec.endReducerIndex
 
-        val isRightSkew = isSkewed(rightActualSizes(partitionIndex), rightMedSize) && canSplitRight
+        val rightActualSize = rightActualSizes(partitionIndex)
+        val isRightSkew = isSkewed(rightActualSize, rightMedSize) && canSplitRight
         val rightPartSpec = right.partitionsWithSizes(partitionIndex)._1
         val isRightCoalesced = rightPartSpec.startReducerIndex + 1 < rightPartSpec.endReducerIndex
 
@@ -200,8 +202,8 @@ case class OptimizeSkewedJoin(conf: SQLConf) extends Rule[SparkPlan] {
           val skewSpecs = createSkewPartitionSpecs(
             left.shuffleStage.shuffle.shuffleDependency.shuffleId, reducerId, leftTargetSize)
           if (skewSpecs.isDefined) {
-            val sizeStr = FileUtils.byteCountToDisplaySize(leftActualSizes(partitionIndex))
-            logDebug(s"Left side partition $partitionIndex ($sizeStr) is skewed, " +
+            logDebug(s"Left side partition $partitionIndex " +
+              s"(${FileUtils.byteCountToDisplaySize(leftActualSize)}) is skewed, " +
               s"split it into ${skewSpecs.get.length} parts.")
             numSkewedLeft += 1
           }
@@ -216,8 +218,8 @@ case class OptimizeSkewedJoin(conf: SQLConf) extends Rule[SparkPlan] {
           val skewSpecs = createSkewPartitionSpecs(
             right.shuffleStage.shuffle.shuffleDependency.shuffleId, reducerId, rightTargetSize)
           if (skewSpecs.isDefined) {
-            val sizeStr = FileUtils.byteCountToDisplaySize(rightActualSizes(partitionIndex))
-            logDebug(s"Right side partition $partitionIndex ($sizeStr) is skewed, " +
+            logDebug(s"Right side partition $partitionIndex " +
+              s"(${FileUtils.byteCountToDisplaySize(rightActualSize)}) is skewed, " +
               s"split it into ${skewSpecs.get.length} parts.")
             numSkewedRight += 1
           }