Re: ecdh support causes unnecessary roundtrips

Hi,

On 2024-06-17 19:51:45 +0200, Daniel Gustafsson wrote:
> > On 17 Jun 2024, at 19:44, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> >> Let's bring that to Erica's patch for allowing a list of curves.
> >
> > I'm kinda wondering if we ought to do something about this in the
> > backbranches. Forcing unnecessary roundtrips onto everyone for the next five
> > years due to an oversight on our part isn't great. Once you're not local, the
> > roundtrip does measurably increase the "time to first query".
>
> I don't disagree, but wouldn't it be the type of behavioural change which we
> typically try to avoid in backbranches?

Yea, it's not great. Not sure what the right thing is here.

> Changing the default of the ecdh GUC would perhaps be doable?

I was wondering whether we could change the default so that it accepts both
x25519 and secp256r1. Unfortunately that seems to requires changing what we
use to set the parameter...

> (assuming that's a working solution to avoid the roundtrip).

It is.

> Amending the documentation is the one thing we certainly can do but 99.9% of
> affected users won't know they are affected so won't look for that section.

Yea. It's also possible that some other bindings changed their default to
match ours...

Greetings,

Andres Freund