[GitHub] [spark] Ngone51 commented on a change in pull request #31476: [SPARK-34366][SQL] Add interface for DS v2 metrics

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Ngone51 commented on a change in pull request #31476:
URL: https://github.com/apache/spark/pull/31476#discussion_r578219652



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File path: sql/catalyst/src/main/java/org/apache/spark/sql/connector/CustomMetric.java
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@@ -0,0 +1,61 @@
+/*
+ * 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.connector;
+
+import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.read.PartitionReader;
+import org.apache.spark.sql.connector.read.Scan;
+
+/**
+ * A custom metric. This is a logical representation of a metric reported by data sources during
+ * read path. Data sources can report supported metric list by {@link Scan} to Spark in query
+ * planning. During query execution, Spark will collect the metrics per partition by
+ * {@link PartitionReader} and combine metrics from partitions to the final result. How Spark
+ * combines metrics depends on the metric type. For streaming query, Spark will collect and combine
+ * metrics for a final result per micro batch.
+ *
+ * The metrics will be gathered during query execution back to the driver and then combined. The
+ * final result will be shown up in the physical operator in Spark UI.
+ *
+ * @since 3.2.0
+ */
+@Evolving
+public interface CustomMetric {
+    /**
+     * Returns the name of custom metric.
+     */
+    String name();
+
+    /**
+     * Returns the description of custom metric.
+     */
+    String description();
+
+    /**
+     * Supported metric type. The metric types must be supported by Spark SQL internal metrics.

Review comment:
       Spark SQL internal metrics always return a long value. Do we still need the `LongMetric` interface if metrics types are limited to SQL internal metrics?




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