[GitHub] [spark] cloud-fan commented on a change in pull request #25007: [SPARK-28209][CORE][SHUFFLE] Proposed new shuffle writer API

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cloud-fan commented on a change in pull request #25007: [SPARK-28209][CORE][SHUFFLE] Proposed new shuffle writer API 
URL: https://github.com/apache/spark/pull/25007#discussion_r310222817
 
 

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 File path: core/src/main/java/org/apache/spark/shuffle/api/ShuffleMapOutputWriter.java
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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.shuffle.api;
+
+import java.io.IOException;
+
+import org.apache.spark.annotation.Private;
+
+/**
+ * :: Private ::
+ * A top-level writer that returns child writers for persisting the output of a map task,
+ * and then commits all of the writes as one atomic operation.
+ *
+ * @since 3.0.0
+ */
+@Private
+public interface ShuffleMapOutputWriter {
+
+  /**
+   * Creates a writer that can open an output stream to persist bytes targeted for a given reduce
+   * partition id.
+   * <p>
+   * The chunk corresponds to bytes in the given reduce partition. This will not be called twice
+   * for the same partition within any given map task. The partition identifier will be in the
+   * range of precisely 0 (inclusive) to numPartitions (exclusive), where numPartitions was
+   * provided upon the creation of this map output writer via
+   * {@link ShuffleExecutorComponents#createMapOutputWriter(int, int, long, int)}.
+   * <p>
+   * Calls to this method will be invoked with monotonically increasing reducePartitionIds; each
 
 Review comment:
   How useful is this? I think we can make Spark shuffle more flexible if we don't guarantee this. Do you have a concrete example of how an implementation can leverage this guarantee?

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