Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/5868#discussion_r29816458
--- Diff:
core/src/main/java/org/apache/spark/shuffle/unsafe/UnsafeShuffleSpillWriter.java
---
@@ -0,0 +1,344 @@
+/*
+ * 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.unsafe;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.LinkedList;
+
+import org.apache.spark.storage.*;
+import scala.Tuple2;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.spark.SparkConf;
+import org.apache.spark.TaskContext;
+import org.apache.spark.executor.ShuffleWriteMetrics;
+import org.apache.spark.serializer.SerializerInstance;
+import org.apache.spark.shuffle.ShuffleMemoryManager;
+import org.apache.spark.unsafe.PlatformDependent;
+import org.apache.spark.unsafe.memory.MemoryBlock;
+import org.apache.spark.unsafe.memory.TaskMemoryManager;
+
+/**
+ * An external sorter that is specialized for sort-based shuffle.
+ * <p>
+ * Incoming records are appended to data pages. When all records have been
inserted (or when the
+ * current thread's shuffle memory limit is reached), the in-memory
records are sorted according to
+ * their partition ids (using a {@link UnsafeShuffleSorter}). The sorted
records are then written
+ * to a single output file (or multiple files, if we've spilled). The
format of the output files is
+ * the same as the format of the final output file written by
+ * {@link org.apache.spark.shuffle.sort.SortShuffleWriter}: each output
partition's records are
+ * written as a single serialized, compressed stream that can be read with
a new decompression and
+ * deserialization stream.
+ * <p>
+ * Unlike {@link org.apache.spark.util.collection.ExternalSorter}, this
sorter does not merge its
+ * spill files. Instead, this merging is performed in {@link
UnsafeShuffleWriter}, which uses a
+ * specialized merge procedure that avoids extra
serialization/deserialization.
+ */
+public final class UnsafeShuffleSpillWriter {
--- End diff --
i'd name this UnsafeShuffleSorter
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