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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.scheduler
import java.io.{Externalizable, ObjectInput, ObjectOutput}
import org.roaringbitmap.RoaringBitmap
import org.apache.spark.storage.BlockManagerId
import org.apache.spark.util.Utils
/**
* Result returned by a ShuffleMapTask to a scheduler. Includes the block manager address that the
* task ran on as well as the sizes of outputs for each reducer, for passing on to the reduce tasks.
*/
private[spark] sealed trait MapStatus {
/** Location where this task was run. */
def location: BlockManagerId
/**
* Estimated size for the reduce block, in bytes.
*
* If a block is non-empty, then this method MUST return a non-zero size. This invariant is
* necessary for correctness, since block fetchers are allowed to skip zero-size blocks.
*/
def getSizeForBlock(reduceId: Int): Long
}
private[spark] object MapStatus {
def apply(loc: BlockManagerId, uncompressedSizes: Array[Long]): MapStatus = {
if (uncompressedSizes.length > 2000) {
HighlyCompressedMapStatus(loc, uncompressedSizes)
} else {
new CompressedMapStatus(loc, uncompressedSizes)
}
}
private[this] val LOG_BASE = 1.1
/**
* Compress a size in bytes to 8 bits for efficient reporting of map output sizes.
* We do this by encoding the log base 1.1 of the size as an integer, which can support
* sizes up to 35 GB with at most 10% error.
*/
def compressSize(size: Long): Byte = {
if (size == 0) {
0
} else if (size <= 1L) {
1
} else {
math.min(255, math.ceil(math.log(size) / math.log(LOG_BASE)).toInt).toByte
}
}
/**
* Decompress an 8-bit encoded block size, using the reverse operation of compressSize.
*/
def decompressSize(compressedSize: Byte): Long = {
if (compressedSize == 0) {
0
} else {
math.pow(LOG_BASE, compressedSize & 0xFF).toLong
}
}
}
/**
* A [[MapStatus]] implementation that tracks the size of each block. Size for each block is
* represented using a single byte.
*
* @param loc location where the task is being executed.
* @param compressedSizes size of the blocks, indexed by reduce partition id.
*/
private[spark] class CompressedMapStatus(
private[this] var loc: BlockManagerId,
private[this] var compressedSizes: Array[Byte])
extends MapStatus with Externalizable {
protected def this() = this(null, null.asInstanceOf[Array[Byte]]) // For deserialization only
def this(loc: BlockManagerId, uncompressedSizes: Array[Long]) {
this(loc, uncompressedSizes.map(MapStatus.compressSize))
}
override def location: BlockManagerId = loc
override def getSizeForBlock(reduceId: Int): Long = {
MapStatus.decompressSize(compressedSizes(reduceId))
}
override def writeExternal(out: ObjectOutput): Unit = Utils.tryOrIOException {
loc.writeExternal(out)
out.writeInt(compressedSizes.length)
out.write(compressedSizes)
}
override def readExternal(in: ObjectInput): Unit = Utils.tryOrIOException {
loc = BlockManagerId(in)
val len = in.readInt()
compressedSizes = new Array[Byte](len)
in.readFully(compressedSizes)
}
}
/**
* A [[MapStatus]] implementation that only stores the average size of non-empty blocks,
* plus a bitmap for tracking which blocks are empty. During serialization, this bitmap
* is compressed.
*
* @param loc location where the task is being executed
* @param numNonEmptyBlocks the number of non-empty blocks
* @param emptyBlocks a bitmap tracking which blocks are empty
* @param avgSize average size of the non-empty blocks
*/
private[spark] class HighlyCompressedMapStatus private (
private[this] var loc: BlockManagerId,
private[this] var numNonEmptyBlocks: Int,
private[this] var emptyBlocks: RoaringBitmap,
private[this] var avgSize: Long)
extends MapStatus with Externalizable {
// loc could be null when the default constructor is called during deserialization
require(loc == null || avgSize > 0 || numNonEmptyBlocks == 0,
"Average size can only be zero for map stages that produced no output")
protected def this() = this(null, -1, null, -1) // For deserialization only
override def location: BlockManagerId = loc
override def getSizeForBlock(reduceId: Int): Long = {
if (emptyBlocks.contains(reduceId)) {
0
} else {
avgSize
}
}
override def writeExternal(out: ObjectOutput): Unit = Utils.tryOrIOException {
loc.writeExternal(out)
emptyBlocks.writeExternal(out)
out.writeLong(avgSize)
}
override def readExternal(in: ObjectInput): Unit = Utils.tryOrIOException {
loc = BlockManagerId(in)
emptyBlocks = new RoaringBitmap()
emptyBlocks.readExternal(in)
avgSize = in.readLong()
}
}
private[spark] object HighlyCompressedMapStatus {
def apply(loc: BlockManagerId, uncompressedSizes: Array[Long]): HighlyCompressedMapStatus = {
// We must keep track of which blocks are empty so that we don't report a zero-sized
// block as being non-empty (or vice-versa) when using the average block size.
var i = 0
var numNonEmptyBlocks: Int = 0
var totalSize: Long = 0
// From a compression standpoint, it shouldn't matter whether we track empty or non-empty
// blocks. From a performance standpoint, we benefit from tracking empty blocks because
// we expect that there will be far fewer of them, so we will perform fewer bitmap insertions.
val emptyBlocks = new RoaringBitmap()
val totalNumBlocks = uncompressedSizes.length
while (i < totalNumBlocks) {
var size = uncompressedSizes(i)
if (size > 0) {
numNonEmptyBlocks += 1
totalSize += size
} else {
emptyBlocks.add(i)
}
i += 1
}
val avgSize = if (numNonEmptyBlocks > 0) {
totalSize / numNonEmptyBlocks
} else {
0
}
new HighlyCompressedMapStatus(loc, numNonEmptyBlocks, emptyBlocks, avgSize)
}
}
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