Re: Add new protocol message to change GUCs for usage with future protocol-only GUCs

On Thu, Aug 15, 2024 at 3:04 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> Perhaps we should even change it to return
> 300000 for protocol version 3.0, and just leave a note in the docs like
> "in older versions of libpq, this returned 3 for protocol version 3.0".

I think that would absolutely break current code. It's not uncommon
(IME) for hand-built clients wrapping libpq to make sure they're not
talking v2 before turning on some feature, and they're allowed to do
that with a PQprotocolVersion() == 3 check. A GitHub code search
brings up examples.

As for 30001: I don't see the value in modifying an exported API in
this way. Especially since we can add a new entry point that will be
guaranteed not to break anyone, as Robert suggested. I think it's a
POLA violation at minimum; my understanding was that up until this
point, the value was incremented during major (incompatible) version
bumps. And I think other users will have had the same understanding.

--Jacob