Re: [PATCH v3 0/4] Additional FAQ entries

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 6, 2024, 17:18 UTC
Message-ID: <xmqqjzhyqw17.fsf@gitster.g>
In-Reply-To: <20240706064758.GG700645@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 17 quoted lines

> On Thu, Jul 04, 2024 at 09:23:28PM +0000, brian m. carlson wrote:
>
>> > Buffering the entire thing will break because ...?  Deadlock?  Or is
>> > there anything more subtle going on?
>> 
>> When we use the smart HTTP protocol, the server sends keep-alive and
>> status messages as one of the data streams, which is important because
>> (a) the user is usually impatient and wants to know what's going on and
>> (b) it may take a long time to pack the data, especially for large
>> repositories, and sending no data may result in the connection being
>> dropped or the client being served a 500 by an intermediate layer.  We
>> know this does happen and I've seen reports of it.
>
> Additionally, I think for non-HTTP transports (think proxying ssh
> through socat or similar), buffering the v0 protocol is likely a total
> disaster. The fetch protocol assumes both sides spewing at each other in
> real time.

Yeah, beyond one "window" that a series of "have"s are allowed to be in flight, no further "have"s are sent before seeing an "ack/nack" response, so if you buffer too much, they can deadlock fairly easily.

> ... So I'm OK
> with just telling people "make sure your proxies aren't buffering" as a
> general rule, rather than trying to get into the nitty gritty of what is
> going to break and how.

Sounds fair.  Thanks.