Bug report

Bug description:

Hello,

Opening a bug ticket before I send a PR.

I just spent yet another day debugging a slow Python application. A task that took 8 seconds out of the box, took 0.3 seconds after adding TCP_NODELAY.
Nothing special, just two processes talking over a localhost TCP socket.

For people not familiar with the matter, nagle algorithm adds a small delay (up to 500ms depending on OS) before sending a packet in some circumstances, this can have a catastrophic effect on network applications depending on their read/write patterns.

This has been a long-standing recurring issue across many applications and libraries. I'd like to set TCP_NODELAY by default on all TCP sockets created by python (socket module), to effectively disables Nagle's algorithm by default.

The last python discussion on this topic was in 2016 https://bugs.python.org/issue27456
There was clear consensus that nagle algorithm should be disabled by default.
This lead to a few patches in built-in modules and third party packages (asyncio and uvloop), some related tickets: python/asyncio#286 python/asyncio#373

10 year have passed since that last discussion.
The bug is still showing up regularly both in the python interpreter and in popular libraries. ( a quick search immediately shows that http.server is affected #108736 )
We should fix it.

For python, I think we can set TCP_NODELAY when a socket is created in the socket module. It's just a few lines of code to change.
Thoughts?

The rest of the world has been actively setting TCP_NODELAY to mitigate the issue:

• GO has set TCP_NODELAY by default since inception
• curl has set TCP_NODELAY since 2016 curl/curl@4732ca5
• NodeJS has set TCP_NODELAY by default since 2020 Follow curl: Enable setNoDelay() / TCP_NODELAY by default on HTTP(S) 1.x nodejs/node#34185
• Rust has TCP_NODELAY in the network libraries (main library is tokio Set tcp nodelay on sockets tokio-rs/axum#2521)
• John Nagle explained himself that the nagle algorithm has been broken since the moment the RFC was published https://news.ycombinator.com/item?id=10608356
• the RFC https://datatracker.ietf.org/doc/html/rfc896
• one article to explain the issue https://brooker.co.za/blog/2024/05/09/nagle.html

Regards

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-144254: set TCP_NODELAY by default (disable nagle algorithm) #144255