dongjoon-hyun commented on code in PR #57355:
URL: https://github.com/apache/spark/pull/57355#discussion_r3641126247


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sql/core/src/main/scala/org/apache/spark/sql/execution/metric/CustomShuffleMetrics.scala:
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@@ -0,0 +1,83 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.metric
+
+import org.apache.spark.SparkContext
+import org.apache.spark.internal.Logging
+import org.apache.spark.internal.LogKeys.METRIC_NAME
+import org.apache.spark.shuffle.api.metric.{CustomShuffleMetric, 
CustomShuffleTaskMetric}
+import org.apache.spark.util.MetricUtils
+
+object CustomShuffleMetrics extends Logging {
+
+  /**
+   * Creates collision-filtered custom shuffle metric [[SQLMetric]]s for an 
operator that already
+   * exposes the given Spark-owned metric names. Plugin metrics whose names 
collide with a
+   * Spark-owned name are dropped so they can't shadow the real accumulators 
(e.g.
+   * `shuffleRecordsWritten`, which feeds AQE). Operators pass the reserved 
names they own; the
+   * declared metrics come from the shuffle driver components.
+   */
+  def createFilteredMetrics(
+      sc: SparkContext,
+      reservedNames: Set[String]): Map[String, SQLMetric] = {
+    val (reserved, allowed) = 
sc.shuffleDriverComponents.supportedCustomMetrics()
+      .partition(metric => reservedNames.contains(metric.name()))
+    if (reserved.nonEmpty) {
+      logWarning(log"Ignoring custom shuffle metrics whose names collide with 
Spark-owned " +
+        log"Exchange metrics: " +
+        log"${MDC(METRIC_NAME, reserved.map(_.name()).sorted.mkString(", 
"))}.")
+    }
+    createMetrics(sc, allowed)
+  }
+
+  /**
+   * Creates [[SQLMetric]]s for the given declared custom shuffle metrics, 
keyed by metric name.
+   */
+  def createMetrics(
+      sc: SparkContext,
+      metrics: Array[CustomShuffleMetric]): Map[String, SQLMetric] = {
+    metrics.map { metric =>
+      val label = metric.description()
+      // AVERAGE_METRIC is intentionally unsupported: its per-task values must 
be stored pre-scaled
+      // via SQLMetric.set(Double), whereas custom task metrics report a plain 
Long.
+      val acc = metric.metricType() match {
+        case MetricUtils.SUM_METRIC => SQLMetrics.createMetric(sc, label)
+        case MetricUtils.SIZE_METRIC => SQLMetrics.createSizeMetric(sc, label)
+        case MetricUtils.TIMING_METRIC => SQLMetrics.createTimingMetric(sc, 
label)
+        case MetricUtils.NS_TIMING_METRIC => 
SQLMetrics.createNanoTimingMetric(sc, label)
+        case other => throw new IllegalArgumentException(

Review Comment:
   This looks like an inconsistent error handling between name collisions and 
invalid metric types.
   
   `createFilteredMetrics` handles the two failure modes differently: a plugin 
metric whose
   name collides with a Spark-owned metric is silently dropped with a warning, 
but an invalid
   `metricType()` throws an `IllegalArgumentException`.
   
   Since the exception is thrown while evaluating the operator's lazy `metrics` 
val (i.e. during
   planning / UI access), a single misconfigured plugin would fail **every 
query that contains a
   shuffle**, rather than just losing the bad metric.
   
   Could we make the two cases consistent? Two options:
   
   1. Treat an invalid metric type the same as a collision: log a warning and 
drop the metric,
      so a buggy plugin degrades gracefully instead of breaking all queries.
   2. If we do want to fail fast on an invalid type, use an error-class-based 
exception
      (e.g. `SparkIllegalArgumentException`) instead of a plain 
`IllegalArgumentException`,
      per the current error framework convention.
   
   I'd lean toward option 1, since custom metrics are purely observability and 
shouldn't be able
   to take down query execution.



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