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

On Thu, Apr 18, 2024 at 3:34 PM Jelte Fennema-Nio <me(at)jeltef(dot)nl> wrote:
> I really don't understand what exactly you're worried about. What do
> you expect will break when bumping the protocol version? As Dave said,
> clients should never bail out due to protocol version differences.

Sure, and I should never forget to take out the trash or mow the lawn.

> So, I don't understand why you seem to view bumping the protocol
> version with so much negativity. We're also bumping PG versions every
> year. Afaik people only like that, partially because it's immediately
> clear that certain features (e.g. MERGE) are not supported when
> connecting to older servers. To me the same is true for bumping the
> protocol version. There are no downsides to bumping it, only upsides.

I see it the exact opposite way around.

If we go with Peter's approach, every driver that supports his feature
will work perfectly, and every driver that doesn't will work exactly
as it does today. The risk of breaking anything is as near to zero as
human developers can reasonably hope to achieve. Nobody who doesn't
care about the feature will have to lift a single finger, today,
tomorrow, or ever. That's absolutely brilliant.

If we instead go with your approach, then anyone who wants to support
3.2 when it materializes will have to also support 3.1, which means
they have to support this feature. That's not a terrible burden, but
it's not a necessary one either. Also, even just 3.1 is going to break
something for somebody. There's just no way that we've left the
protocol version unchanged for this long and the first change we make
doesn't cause some collateral damage.

Sure, those are minor downsides in the grand scheme of things. But
AFAICS the only downside of Peter's approach that you've alleged is
that doesn't involve bumping the version number. Of course, if bumping
the version number is an intrinsic good, then no further justification
is required, but I don't buy that. I do not believe that users or
maintainers will throw us a pizza party when they find out that we've
changed the version number. There's no reason for anyone to be happy
about that for its own sake.

--
Robert Haas
EDB: http://www.enterprisedb.com