Re: Remove Deprecated Exclusive Backup Mode

On 2019-02-25 08:42:02 -0500, Stephen Frost wrote:
> Greetings,
>
> * Andres Freund (andres(at)anarazel(dot)de) wrote:
> > On 2019-02-24 17:19:22 -0500, Stephen Frost wrote:
> > > You say above that the new interface is unquestionably an improvement
> >
> > FWIW, I think we didn't design it even remotely as well as we ought to
> > have. It was both a mistake to not offer a version of non-exclusive
> > backups that works with a client connection (for integration with the
> > TSMs of this world), and it was a mistake not to offer a commandline
> > tool that does the non-exclusive pg/start backup.
>
> I'm not really following- did you mean to say "without a client
> connection" above?

Yes.

> We could still add some kind of commandline tool to help with the
> non-exclusive pg start/stop backup

That doesn't help, as long as the connection requirement is there. As
explained elsewhere in this thread, a lot of larger external backup
infrastructure just gives you a start/stop hook, and that makes using a
persistent connection hard and fragile.

> but I'm not really sure exactly what that would look like and I
> honestly don't have terribly much interest in spending resources on
> implementing it since it would lack a great many features that we'd
> then end up wanting to add on... and then we end up backing into
> building yet another backup tool.

Meh. You are proposing to remove a feature (even if a dangerous
one). Requiring some minimal compat work to make htat more palpaple
isn't crazy. Nor does using backrest or whatnot do *ANYTHING* about the
users of large company wide backup tools.

> > > I really, honestly, believe what we need to *stop* doing is trying to
> > > drag along support for old/deprecated interfaces after we've introduced
> > > new ones, thus avoiding these arguments and the time spent on them, and
> > > the time spent dealing with implementing and documenting new APIs around
> > > old ones. The only thing it seems to unquestionably do is make us argue
> > > about when we are going to *finally* rip out the old/deprecated API (or
> > > interface, or whatever you want to call it).
> >
> > While I agree that we should remove non-exclusive backups, I VEHEMENTLY
> > oppose the unconditionality of the above statement. Yes, it's annoying
> > to keep interfaces around, but unnecessarily inflicting pain to everyone
> > also is annoying.
>
> Alright, then how about we provide a bit of help for everyone who's got
> a system built around recovery.conf today, instead of just completely
> ripping that out?

Oh, comeon. Obviously we're sometimes going to have to make breaking
changes. But you're essentially arguing that we shouldn't provide compat
where we can come up with a reasonable way to provide backward
compatibility. And I think that's crazy and will hurt postgres.

> > That's not to say we shouldn't be better at announcing and then
> > following through on the deprecation of old interfaces.
>
> We announce things have changed every year, and people have five years
> from that point, during which we'll continue to support them and fix
> bugs and deal with security issues, to make whatever changes they need
> to for the new interface.
>
> The argument seems to be that people want new features but they don't
> want to have to do any work to get those new features.

I mean, duh? We can't make that happen all the time, but I don't
understand why it's surprising to have that as *one* goal that's in
conflict with other goals? Your analysis also neglects that a lot of
software will have to work across multiple supported versions of
postgres (at the very least in prep for the migration, but also often
longer) - by having a few versions were both interfaces work, that can
be made *MUCH* less painful.

> When is something too big of a change to make in a given major version
> and we have to, instead, provide backwards compatibility for it? What
> is that policy? How many releases do we have to support it for? How do
> we communicate that to our users, so that they know what they can depend
> on being there across major releases and what they can't?

I literally said that we should have more policy around this.

I'm going to stop here, discussing with you in this thread seems
unproductive.

Greetings,

Andres Freund