[GitHub] [spark] hvanhovell commented on a change in pull request #26127: [SPARK-29348][SQL] Add observable Metrics for Streaming queries

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hvanhovell commented on a change in pull request #26127: [SPARK-29348][SQL] Add observable Metrics for Streaming queries
URL: https://github.com/apache/spark/pull/26127#discussion_r352881909
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/CollectMetricsExec.scala
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+/*
+ * 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
+
+import scala.collection.mutable
+
+import org.apache.spark.TaskContext
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.Row
+import org.apache.spark.sql.catalyst.{CatalystTypeConverters, InternalRow}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, NamedExpression, SortOrder}
+import org.apache.spark.sql.catalyst.plans.physical.Partitioning
+import org.apache.spark.sql.types.StructType
+
+/**
+ * Collect arbitrary (named) metrics from a [[SparkPlan]].
+ */
+case class CollectMetricsExec(
+    name: String,
+    metricExpressions: Seq[NamedExpression],
+    child: SparkPlan)
+  extends UnaryExecNode {
+
+  private lazy val accumulator: AggregatingAccumulator = {
+    val acc = AggregatingAccumulator(metricExpressions, child.output)
+    acc.register(sparkContext, Option("Collected metrics"))
+    acc
+  }
+
+  val metricsSchema: StructType = {
+    StructType.fromAttributes(metricExpressions.map(_.toAttribute))
+  }
+
+  private lazy val toRowConverter: InternalRow => Row = {
+    CatalystTypeConverters.createToScalaConverter(metricsSchema)
+      .asInstanceOf[InternalRow => Row]
+  }
+
+  def collectedMetrics: Row = toRowConverter(accumulator.value)
+
+  override def output: Seq[Attribute] = child.output
+
+  override def outputPartitioning: Partitioning = child.outputPartitioning
+
+  override def outputOrdering: Seq[SortOrder] = child.outputOrdering
 
 Review comment:
   I don't think we should. If we do that we might eliminate a CollectMetrics operator when reuse exchanges.

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