net: enable TCP_NODELAY by default on all platforms

[silverwind]

Just saw nodejs/node-v0.x-archive#9235 and this might be a good addition for platform consistency for us too. I'm just not sure if the proposed patch is the best place to put the call.

[silverwind]

I may have to dig deeper here. Windows for example doesn't default to TCP_NODELAY either, so it seems questionable if we would rely in platform defaults like the issue implies.

[meandmycode]

+1 seems like a bug, my initial thought was the docs should be changed but it seems like nodelay is highly recommended as default for today's networking. I would hazard a guess that os platforms not already doing this are playing it safe where as iojs can be more reactive to current practice.

[silverwind]

Yes, Nagle's algorithm isn't really beneficial in today's latency-limited networks. I wonder if it's possible to test from JS whether it is enabled on a target host.

[mscdex]

+1

[brendanashworth]

+1 from me too, I'd love to see this.

[bnoordhuis]

The fact that the documentation says that TCP_NODELAY is enabled by default seems like a documentation bug to me. As far as I know, that has never been true.

I'm on the fence as to whether it's a good idea to enable it by default. I'd be more comfortable +1'ing that if I had more faith in the net module's capabilities of batching writes. That's not to say I object, just that I'm not sure if defaulting to TCP_NODELAY is an unequivocally good thing.

[silverwind]

If we go through with it enabling it everywhere, we need an mechanism for the users to disable it globally too. I think ideally on a per-process basis, maybe something like process.setNoDelay().

The reason is simple: With net only exposing this option on single sockets, there no way every module is going to expose the option to its parent.

[silverwind]

I think regardless if we enable it by default or not, a process.setNoDelay() could generally prove useful.

While it can be set at kernel-level, I think controlling it on a per-program basis is preferred. For example, nginx has the option to set it per-server.

[sam-github]

@bnoordhuis I wonder if adding a net.setNoDelay() to allow the default to be changed would be useful. Users in the field who are trying to squeeze more performance out could report back if any of them actually find the feature useful. If noone finds it useful to change no delay globally, there's no reason to change the default.

[silverwind]

A net.setNoDelay() was my first idea too, but if I understand this correctly, that would require the user to require('net') before anything else to work on all connections following the call. We probably don't want the require order to be significant.

Or would it be possible to apply TCP_NODELAY retroactively to all sockets of a program?

[piscisaureus]

I generally dislike any type of "global" setting. You wanted to speed up your http server but without realizing the database driver just got slower.

Node should pick reasonable defaults (so maybe switch it on by default), behave consistently on all platforms (fix windows and/or aix), and be easy to configure (maybe setNoDelay is too difficult for http servers). Let's keep bikeshedding withing this parameter space.

[silverwind]

As a first step, I'm trying to verify that setNoDelay is working when set on both client and server:

"use strict";
const net = require("net");
const port = 4000;
let timeClient, timeServer;

function time() {
    let hrtime = process.hrtime();
    return hrtime[0] * 1e9 + hrtime[1];
}

net.createServer(function(socket) {
    socket.setNoDelay(true); // correct?
    timeServer = time();
    socket.write("\0");
    socket.on("data", function () {
        console.log("Client -> Server " + ((time() - timeClient) / 1000).toFixed(0) + "µs");
    });
}).listen(port);

setInterval(function() {
    let socket = new net.Socket();
    socket.setNoDelay(true); // correct?
    socket.on("data", function () {
        console.log("Server -> Client " + ((time() - timeServer) / 1000).toFixed(0) + "µs");
        timeClient = time();
        socket.write("\0");
        socket.end();
    }).connect(port);
}, 200);

Is this the correct usage? @evanlucas maybe you can have a look, as you've dealt with these socket options recently.

edit: updated to measure both delays. also: i fail at math, it's µs :)
edit2: I probably need to send out writes way faster to notice the nagling.