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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2022/10/20 04:12:01 UTC
[GitHub] [spark] sadikovi commented on a diff in pull request #38064: [SPARK-40622][SQL][CORE]Result of a single task in collect() must fit in 2GB
sadikovi commented on code in PR #38064:
URL: https://github.com/apache/spark/pull/38064#discussion_r1000114683
##########
core/src/main/scala/org/apache/spark/serializer/SerializerHelper.scala:
##########
@@ -0,0 +1,51 @@
+/*
+ * 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.serializer
+
+import java.nio.ByteBuffer
+
+import scala.reflect.ClassTag
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.util.io.{ChunkedByteBuffer, ChunkedByteBufferOutputStream}
+
+private[spark] object SerializerHelper extends Logging {
+
+ /**
+ * @param estimatedSize estimated size of `t`, used as a hint to choose proper chunk size
+ */
+ def serializeToChunkedBuffer[T: ClassTag](
+ serializerInstance: SerializerInstance,
+ t: T,
Review Comment:
nit: could you have a bit more descriptive name? Thanks.
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -42,8 +42,9 @@ import org.apache.spark.util.Utils
* buffers may also be used elsewhere then the caller is responsible for copying
* them as needed.
*/
-private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
+private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) extends Externalizable {
Review Comment:
Can you confirm that these are copies of the byte buffers so there is no other reference that can be modified outside of the ChunkedByteBuffer based on your changes?
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -84,6 +91,57 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
}
}
+ /**
+ * write to ObjectOutput with zero copy if possible
Review Comment:
nit: `Writes to the provided ObjectOutput with zero copy if possible.`
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -207,6 +267,18 @@ private[spark] object ChunkedByteBuffer {
}
out.toChunkedByteBuffer
}
+
+ /**
+ * Try to estimate appropriate chunk size so that it's not too large(waste memory) or too
+ * small(too many segments)
Review Comment:
nit: space before (.
##########
core/src/test/scala/org/apache/spark/io/ChunkedByteBufferSuite.scala:
##########
@@ -69,6 +78,45 @@ class ChunkedByteBufferSuite extends SparkFunSuite with SharedSparkContext {
}
}
+ test("Externalizable: writeExternal() and readExternal()") {
+ // intentionally generate arrays of different len, in order to verify the chunks layout
+ // is preserved after ser/deser
+ val byteArrays = (1 to 15).map(i => (0 until i).map(_.toByte).toArray)
+ val chunkedByteBuffer = new ChunkedByteBuffer(byteArrays.map(ByteBuffer.wrap).toArray)
+ val baos = new ByteArrayOutputStream()
+ val objOut = new ObjectOutputStream(baos)
+ chunkedByteBuffer.writeExternal(objOut)
+ objOut.close()
+ assert(chunkedByteBuffer.chunks.forall(_.position() == 0))
+
+ val chunkedByteBuffer2 = {
+ val tmp = new ChunkedByteBuffer
+ tmp.readExternal(new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray)))
+ tmp
+ }
+ assertBufferEqual(chunkedByteBuffer, chunkedByteBuffer2)
+ }
+
+ test(
+ "Externalizable: writeExternal() and readExternal() should handle off-heap buffer properly") {
Review Comment:
nit:
```
....
) {
val ...
```
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -84,6 +91,57 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
}
}
+ /**
+ * write to ObjectOutput with zero copy if possible
Review Comment:
Also, could you elaborate on zero copy? It seems a copy is required regardless.
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -84,6 +91,57 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
}
}
+ /**
+ * write to ObjectOutput with zero copy if possible
+ */
+ override def writeExternal(out: ObjectOutput): Unit = {
+ // we want to keep the chunks layout
+ out.writeInt(chunks.length)
+ val chunksCopy = getChunks()
+ chunksCopy.foreach(buffer => out.writeInt(buffer.limit()))
+ var buffer: Array[Byte] = null
+ val bufferLen = ChunkedByteBuffer.estimateBufferChunkSize(size)
+
+ chunksCopy.foreach { chunk => {
+ if (chunk.hasArray) {
+ // zero copy if the bytebuffer is backed by bytes array
+ out.write(chunk.array(), chunk.arrayOffset(), chunk.limit())
Review Comment:
I believe this would still incur a copy, unless the implementation stores the reference and position.
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -56,7 +57,13 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
/**
* This size of this buffer, in bytes.
*/
- val size: Long = chunks.map(_.limit().asInstanceOf[Long]).sum
+ private var _size: Long = chunks.map(_.limit().asInstanceOf[Long]).sum
Review Comment:
Is this needed for serialisation? Can you add a comment to explain why this is `var`? Thanks.
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -84,6 +91,57 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
}
}
+ /**
+ * write to ObjectOutput with zero copy if possible
+ */
+ override def writeExternal(out: ObjectOutput): Unit = {
+ // we want to keep the chunks layout
Review Comment:
nit: We.... Can you uppercase other comments in the method as well?
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -84,6 +91,57 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
}
}
+ /**
+ * write to ObjectOutput with zero copy if possible
+ */
+ override def writeExternal(out: ObjectOutput): Unit = {
+ // we want to keep the chunks layout
+ out.writeInt(chunks.length)
+ val chunksCopy = getChunks()
+ chunksCopy.foreach(buffer => out.writeInt(buffer.limit()))
+ var buffer: Array[Byte] = null
+ val bufferLen = ChunkedByteBuffer.estimateBufferChunkSize(size)
+
+ chunksCopy.foreach { chunk => {
+ if (chunk.hasArray) {
+ // zero copy if the bytebuffer is backed by bytes array
+ out.write(chunk.array(), chunk.arrayOffset(), chunk.limit())
+ } else {
+ // fallback to copy approach
+ if (buffer == null) {
+ buffer = new Array[Byte](bufferLen)
+ }
+ var bytesToRead = Math.min(chunk.remaining(), bufferLen)
+ while (bytesToRead > 0) {
+ chunk.get(buffer, 0, bytesToRead)
+ out.write(buffer, 0, bytesToRead)
+ bytesToRead = Math.min(chunk.remaining(), bufferLen)
+ }
+ }
+ }}
+ }
+
+ override def readExternal(in: ObjectInput): Unit = {
+ val chunksNum = in.readInt()
+ val indices = 0 until chunksNum
+ val chunksSize = indices.map(_ => in.readInt())
+ val chunks = new Array[ByteBuffer](chunksNum)
+
+ // We deserialize all chunks into on-heap buffer by default. If we have use case in the future
+ // where we want to preserve the on-heap/off-heap nature of chunks, then we need to record the
+ // `isDirect` property of each chunk during serialization
+ indices.foreach { i => {
Review Comment:
nit: you don't need the second `{`.
##########
core/src/test/scala/org/apache/spark/io/ChunkedByteBufferSuite.scala:
##########
@@ -28,6 +29,14 @@ import org.apache.spark.util.io.ChunkedByteBuffer
class ChunkedByteBufferSuite extends SparkFunSuite with SharedSparkContext {
+ def assertBufferEqual(buffer1: ChunkedByteBuffer, buffer2: ChunkedByteBuffer): Unit = {
+ assert(buffer1.chunks.length == buffer2.chunks.length)
+ assert(buffer1.chunks.zip(buffer2.chunks).forall{
Review Comment:
nit: space before {.
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -207,6 +267,18 @@ private[spark] object ChunkedByteBuffer {
}
out.toChunkedByteBuffer
}
+
+ /**
+ * Try to estimate appropriate chunk size so that it's not too large(waste memory) or too
Review Comment:
nit: space before (.
##########
core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala:
##########
@@ -207,6 +267,18 @@ private[spark] object ChunkedByteBuffer {
}
out.toChunkedByteBuffer
}
+
+ /**
+ * Try to estimate appropriate chunk size so that it's not too large(waste memory) or too
+ * small(too many segments)
+ */
+ def estimateBufferChunkSize(estimatedSize: Long = -1): Int = {
+ if (estimatedSize < 0) {
+ CHUNK_BUFFER_SIZE
+ } else {
+ Math.max(Math.min(estimatedSize >> 3, CHUNK_BUFFER_SIZE).toInt, MINIMUM_CHUNK_BUFFER_SIZE)
Review Comment:
+1
##########
core/src/main/scala/org/apache/spark/serializer/SerializerHelper.scala:
##########
@@ -0,0 +1,51 @@
+/*
+ * 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.serializer
+
+import java.nio.ByteBuffer
+
+import scala.reflect.ClassTag
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.util.io.{ChunkedByteBuffer, ChunkedByteBufferOutputStream}
+
+private[spark] object SerializerHelper extends Logging {
Review Comment:
I was thinking if this is specific to the chunked byte buffer, would it be beneficial to add this to ChunkedByteBuffer as a static method, e.g. `ChunkedByteBuffer.serialize(...)`? Just a question to see if there is a utility in the separate class.
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