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

Jacob Champion <jacob.champion@enterprisedb.com>

From: Jacob Champion <jacob.champion@enterprisedb.com>

To: Heikki Linnakangas <hlinnaka@iki.fi>

Cc: Jelte Fennema-Nio <postgres@jeltef.nl>, Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Jacob Burroughs <jburroughs@instructure.com>, Dave Cramer <davecramer@gmail.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, "Andrey M. Borodin" <x4mmm@yandex-team.ru>, Pavel Stehule <pavel.stehule@gmail.com>, Jeff Davis <pgsql@j-davis.com>, Peter Eisentraut <peter@eisentraut.org>

Date: 2024-08-15T22:39:00Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

libpq: Add min/max_protocol_version connection options
- 285613c60a7a 18.0 landed
libpq: Handle NegotiateProtocolVersion message differently
- 5070349102af 18.0 landed
Add PQfullProtocolVersion() to surface the precise protocol version.
- cdb6b0fdb0b2 18.0 landed
Do not hardcode PG_PROTOCOL_LATEST in NegotiateProtocolVersion
- 516b87502dc1 18.0 landed
libpq: Handle NegotiateProtocolVersion message
- bbf9c282ce92 16.0 cited
Provide for forward compatibility with future minor protocol versions.
- ae65f6066dc3 11.0 cited

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