Question

I’m having a use case where I’m sending data via TCP/IP in one direction. I’m doing this via multiple send()-calls with very small (in relation to the size of an ethernet frame) payloads (without any flags for the send()-call). To prevent bloating up my small payload packets to the size of a full ethernet frame, I thought it would be nice to use the TCP_CORK socket option. This works, but when actually comparing the situation before and after using TCP_CORK, I noticed that this kind of aggregation was already done. Why is this so? As I said, I do not use any flags for send() (like MSG_MORE) or other socket options, so I would have expected my original solution to be wasteful.

Answer 1

If you are sending messages very quickly you may be seeing the Nagle algorithm at work. You have to disable it explicitly. Iirc in linux you have to set TCP_NODELAY, but there are different options in other operating systems.