CODEWITHSUNDEEP
javanetty
Felix
Felix

Reputation: 185

How to minimize data copy in Netty/jvm when broadcast message to large number of channel

I'm working on a project which needs to broadcast small messages (<100byte) to thousands of client channels. What is the most efficient way to minimize data copy for every channel by both Netty and JDK?

If use N instances of DuplicatedByteBuf wrapping a shared DirectByteBuf(pooled or unpooled), could the Direct ByteBuffer object in netty's DirectByteBuf be used by JDK instead of copying a new ByteBuffer for every SocketChannel?

Upvotes: 1

Views: 418

Answers (2)

Dmitriy Dumanskiy
Dmitriy Dumanskiy

Reputation: 12817

You have few options :

Option 1. Messages share same data (your 100 bytes) but you have overhead for every retainedDuplicate() call as it creates new buffer instance (even it shares 100 bytes) : 

ByteBuf msg = createMessage(); //pooled, unpooled

for (Channel target : targets) {
    target.writeAndFlush(msg.retainedDuplicate());
}

this is option is not very good for your case as your messages are small.

Options 2. You always use same message but you have to handle message read/write indexes by your own.

ByteBuf msg = createMessage(); //pooled, unpooled
if (targets.size() > 1) {
   msg.retain(targetsNum - 1).markReaderIndex();
}

for (Channel target : targets) {
    target.writeAndFlush(msg);
    if (msg.refCnt() > 0) {
       msg.resetReaderIndex();
    }
}

This option is better for your case. As you create message only once and after message is passed to 1 receiver you will reuse it again for next receiver.

Upvotes: 1

ZHAO Bo
ZHAO Bo

Reputation: 71

The buffer will not be copied when it's written to outbound channels.
As far as I know the 'write' will invoke HeapByteBuffer.duplicate, which is a shallow copy.

Upvotes: 0

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