Thanks to parent (after edit) for really testing. It turns out that he was right that Go on Mac is substantially worse than Linux - my bad. Maybe the Go lib authors didn't put much effort into reading the subtly different BSD/Darwin vs Linux syscall semantics.

To explain the Nagle algorithm's irrelevance to this case, we have to understand how it works. It doesn't delay any writes once you read. It only affects two consecutive small writes (my memory was fuzzy so I checked http://en.wikipedia.org/wiki/Nagle's_algorithm ). Odds of preemption between the client's write and its read seem small, so it shouldn't matter whether you Nagle or not.