Github user WenboZhao commented on a diff in the pull request:
https://github.com/apache/spark/pull/21593#discussion_r196939992
--- Diff:
common/network-common/src/main/java/org/apache/spark/network/protocol/MessageWithHeader.java
---
@@ -137,30 +137,15 @@ protected void deallocate() {
}
private int copyByteBuf(ByteBuf buf, WritableByteChannel target) throws
IOException {
- ByteBuffer buffer = buf.nioBuffer();
- int written = (buffer.remaining() <= NIO_BUFFER_LIMIT) ?
- target.write(buffer) : writeNioBuffer(target, buffer);
+ // SPARK-24578: cap the sub-region's size of returned nio buffer to
improve the performance
+ // for the case that the passed-in buffer has too many components.
+ int length = Math.min(buf.readableBytes(), NIO_BUFFER_LIMIT);
+ ByteBuffer buffer = buf.nioBuffer(buf.readerIndex(), length);
--- End diff --
Thanks @squito and @zsxwing. I would prefer to do it in a different PR with
more careful benchmark and testing. As @squito, that change is more prone to
bugs.
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