Github user zsxwing commented on a diff in the pull request:
https://github.com/apache/spark/pull/12083#discussion_r58259276
--- Diff:
common/network-common/src/main/java/org/apache/spark/network/protocol/MessageWithHeader.java
---
@@ -44,6 +45,14 @@
private long totalBytesTransferred;
/**
+ * When the write buffer size is larger than this limit, I/O will be
done in chunks of this size.
+ * The size should not be too large as it will waste underlying memory
copy. e.g. If network
+ * avaliable buffer is smaller than this limit, the data cannot be sent
within one single write
+ * operation while it still will make memory copy with this size.
+ */
+ private static final int NIO_BUFFER_LIMIT = 512 * 1024;
--- End diff --
What if we create DirectByteBuffer here manually for a big buf (big enough
so that we can get benefits even if creating a direct buffer is slow) and try
to write as many as possible? Then we can avoid the memory copy in
`IOUtil.write`.
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