Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/5868#discussion_r30176759
--- Diff:
core/src/main/java/org/apache/spark/shuffle/unsafe/UnsafeShuffleExternalSorter.java
---
@@ -0,0 +1,418 @@
+/*
+ * 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.LinkedList;
+
+import scala.Tuple2;
+
+import com.google.common.annotations.VisibleForTesting;
+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.storage.*;
+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.
+ */
+final class UnsafeShuffleExternalSorter {
+
+ private final Logger logger =
LoggerFactory.getLogger(UnsafeShuffleExternalSorter.class);
+
+ private static final int PAGE_SIZE =
PackedRecordPointer.MAXIMUM_PAGE_SIZE_BYTES;
+ @VisibleForTesting
+ static final int DISK_WRITE_BUFFER_SIZE = 1024 * 1024;
+ @VisibleForTesting
+ static final int MAX_RECORD_SIZE = PAGE_SIZE - 4;
+
+ private final int initialSize;
+ private final int numPartitions;
+ private final TaskMemoryManager memoryManager;
+ private final ShuffleMemoryManager shuffleMemoryManager;
+ private final BlockManager blockManager;
+ private final TaskContext taskContext;
+ private final boolean spillingEnabled;
+ private final ShuffleWriteMetrics writeMetrics;
+
+ /** The buffer size to use when writing spills using
DiskBlockObjectWriter */
+ private final int fileBufferSize;
+
+ /**
+ * Memory pages that hold the records being sorted. The pages in this
list are freed when
+ * spilling, although in principle we could recycle these pages across
spills (on the other hand,
+ * this might not be necessary if we maintained a pool of re-usable
pages in the TaskMemoryManager
+ * itself).
+ */
+ private final LinkedList<MemoryBlock> allocatedPages = new
LinkedList<MemoryBlock>();
+
+ private final LinkedList<SpillInfo> spills = new LinkedList<SpillInfo>();
+
+ // All three of these variables are reset after spilling:
+ private UnsafeShuffleSorter sorter;
+ private MemoryBlock currentPage = null;
+ private long currentPagePosition = -1;
+ private long freeSpaceInCurrentPage = 0;
+
+ public UnsafeShuffleExternalSorter(
+ TaskMemoryManager memoryManager,
+ ShuffleMemoryManager shuffleMemoryManager,
+ BlockManager blockManager,
+ TaskContext taskContext,
+ int initialSize,
+ int numPartitions,
+ SparkConf conf,
+ ShuffleWriteMetrics writeMetrics) throws IOException {
+ this.memoryManager = memoryManager;
+ this.shuffleMemoryManager = shuffleMemoryManager;
+ this.blockManager = blockManager;
+ this.taskContext = taskContext;
+ this.initialSize = initialSize;
+ this.numPartitions = numPartitions;
+ this.spillingEnabled = conf.getBoolean("spark.shuffle.spill", true);
+ // Use getSizeAsKb (not bytes) to maintain backwards compatibility for
units
+ this.fileBufferSize = (int)
conf.getSizeAsKb("spark.shuffle.file.buffer", "32k") * 1024;
+ this.writeMetrics = writeMetrics;
+ openSorter();
+ }
+
+ /**
+ * Allocates a new sorter. Called when opening the spill writer for the
first time and after
+ * each spill.
+ */
+ private void openSorter() throws IOException {
+ // TODO: move this sizing calculation logic into a static method of
sorter:
+ final long memoryRequested = initialSize * 8L;
+ if (spillingEnabled) {
+ final long memoryAcquired =
shuffleMemoryManager.tryToAcquire(memoryRequested);
+ if (memoryAcquired != memoryRequested) {
+ shuffleMemoryManager.release(memoryAcquired);
+ throw new IOException("Could not acquire memory!");
+ }
+ }
+
+ this.sorter = new UnsafeShuffleSorter(initialSize);
+ }
+
+ /**
+ * Sorts the in-memory records and writes the sorted records to a spill
file.
+ * This method does not free the sort data structures.
+ *
+ * @param isSpill if true, this indicates that we're writing a spill and
that bytes written should
+ * be counted towards shuffle spill metrics rather than
shuffle write metrics.
+ */
+ private void writeSpillFile(boolean isSpill) throws IOException {
--- End diff --
I went with `writeSortedFile` to emphasize that this writes a new file.
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