New submission from STINNER Victor <vstin...@python.org>:
Currently, socket.socket.listen() called with no argument limits the default
backlog to 128:
/* We try to choose a default backlog high enough to avoid connection drops
* for common workloads, yet not too high to limit resource usage. */
int backlog = Py_MIN(SOMAXCONN, 128);
I just saw an article suggesting to use 4096 instead:
https://blog.cloudflare.com/syn-packet-handling-in-the-wild/
On my Fedora 30, listen() manual page says:
The behavior of the backlog argument on TCP sockets changed with Linux
2.2. Now it specifies the queue length for completely established
sockets waiting to be accepted, instead of the number of incomplete
connection requests. The maximum length of the queue for incomplete
sockets can be set using /proc/sys/net/ipv4/tcp_max_syn_backlog. When
syncookies are enabled there is no logical maximum length and this set‐
ting is ignored. See tcp(7) for more information.
If the backlog argument is greater than the value in
/proc/sys/net/core/somaxconn, then it is silently truncated to that
value; the default value in this file is 128. In kernels before
2.4.25, this limit was a hard coded value, SOMAXCONN, with the value
128.
Python 3.8 new socket.create_server() calls sock.listen() by default: so use
Py_MIN(SOMAXCONN, 128) by default.
----------
components: Library (Lib)
messages: 356037
nosy: giampaolo.rodola, vstinner
priority: normal
severity: normal
status: open
title: socket: change listen() default backlog from 128 to 4096?
versions: Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue38699>
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