[SPARK-14290][CORE][NETWORK] avoid significant memory copy in netty's transferTo
## What changes were proposed in this pull request? When netty transfer data that is not `FileRegion`, data will be in format of `ByteBuf`, If the data is large, there will occur significant performance issue because there is memory copy underlying in `sun.nio.ch.IOUtil.write`, the CPU is 100% used, and network is very low. In this PR, if data size is large, we will split it into small chunks to call `WritableByteChannel.write()`, so that avoid wasting of memory copy. Because the data can't be written within a single write, and it will call `transferTo` multiple times. ## How was this patch tested? Spark unit test and manual test. Manual test: `sc.parallelize(Array(1,2,3),3).mapPartitions(a=>Array(new Array[Double](1024 * 1024 * 50)).iterator).reduce((a,b)=> a).length` For more details, please refer to [SPARK-14290](https://issues.apache.org/jira/browse/SPARK-14290) Author: Zhang, Liye <liye.zhang@intel.com> Closes #12083 from liyezhang556520/spark-14290.
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@ -18,6 +18,7 @@
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package org.apache.spark.network.protocol;
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import java.io.IOException;
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import java.nio.ByteBuffer;
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import java.nio.channels.WritableByteChannel;
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import javax.annotation.Nullable;
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@ -43,6 +44,14 @@ class MessageWithHeader extends AbstractReferenceCounted implements FileRegion {
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private final long bodyLength;
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private long totalBytesTransferred;
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/**
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* When the write buffer size is larger than this limit, I/O will be done in chunks of this size.
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* The size should not be too large as it will waste underlying memory copy. e.g. If network
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* avaliable buffer is smaller than this limit, the data cannot be sent within one single write
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* operation while it still will make memory copy with this size.
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*/
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private static final int NIO_BUFFER_LIMIT = 256 * 1024;
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/**
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* Construct a new MessageWithHeader.
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*
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@ -128,8 +137,27 @@ class MessageWithHeader extends AbstractReferenceCounted implements FileRegion {
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}
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private int copyByteBuf(ByteBuf buf, WritableByteChannel target) throws IOException {
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int written = target.write(buf.nioBuffer());
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ByteBuffer buffer = buf.nioBuffer();
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int written = (buffer.remaining() <= NIO_BUFFER_LIMIT) ?
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target.write(buffer) : writeNioBuffer(target, buffer);
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buf.skipBytes(written);
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return written;
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}
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private int writeNioBuffer(
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WritableByteChannel writeCh,
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ByteBuffer buf) throws IOException {
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int originalLimit = buf.limit();
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int ret = 0;
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try {
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int ioSize = Math.min(buf.remaining(), NIO_BUFFER_LIMIT);
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buf.limit(buf.position() + ioSize);
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ret = writeCh.write(buf);
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} finally {
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buf.limit(originalLimit);
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}
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return ret;
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}
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}
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