[SPARK-24578][CORE] Cap sub-region's size of returned nio buffer
## What changes were proposed in this pull request? This PR tries to fix the performance regression introduced by SPARK-21517. In our production job, we performed many parallel computations, with high possibility, some task could be scheduled to a host-2 where it needs to read the cache block data from host-1. Often, this big transfer makes the cluster suffer time out issue (it will retry 3 times, each with 120s timeout, and then do recompute to put the cache block into the local MemoryStore). The root cause is that we don't do `consolidateIfNeeded` anymore as we are using ``` Unpooled.wrappedBuffer(chunks.length, getChunks(): _*) ``` in ChunkedByteBuffer. If we have many small chunks, it could cause the `buf.notBuffer(...)` have very bad performance in the case that we have to call `copyByteBuf(...)` many times. ## How was this patch tested? Existing unit tests and also test in production Author: Wenbo Zhao <wzhao@twosigma.com> Closes #21593 from WenboZhao/spark-24578.
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@ -137,30 +137,15 @@ class MessageWithHeader extends AbstractFileRegion {
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}
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private int copyByteBuf(ByteBuf buf, WritableByteChannel target) throws IOException {
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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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// SPARK-24578: cap the sub-region's size of returned nio buffer to improve the performance
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// for the case that the passed-in buffer has too many components.
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int length = Math.min(buf.readableBytes(), NIO_BUFFER_LIMIT);
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ByteBuffer buffer = buf.nioBuffer(buf.readerIndex(), length);
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int written = target.write(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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@Override
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public MessageWithHeader touch(Object o) {
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super.touch(o);
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