Re: backup manifests

Greetings,

* Robert Haas (robertmhaas(at)gmail(dot)com) wrote:
> On Thu, Mar 26, 2020 at 4:37 PM David Steele <david(at)pgmasters(dot)net> wrote:
> > I agree with Stephen that this should be done, but I agree with you that
> > it can wait for a future commit. However, I do think:
> >
> > 1) It should be called out rather plainly in the documentation.
> > 2) If there are files in pg_wal then pg_validatebackup should inform the
> > user that those files have not been validated.
>
> I agree with you about #1, and I suspect that there's a way to improve
> what I've got here now, but I think I might be too close to this to
> figure out what the best way would be, so suggestions welcome.
>
> I think #2 is an interesting idea and could possibly reduce the danger
> of user confusion on this point considerably - because, let's face it,
> not everyone is going to read the documentation. However, I'm having a
> hard time figuring out exactly what we'd print. Right now on success,
> unless you specify -q, you get:
>
> [rhaas ~]$ pg_validatebackup ~/pgslave
> backup successfully verified
>
> But it feels strange and possibly confusing to me to print something like:
>
> [rhaas ~]$ pg_validatebackup ~/pgslave
> backup successfully verified (except for pg_wal)
>
> ...because there are a few other exceptions too, and also because it

The exceptions you're referring to here are things like the various
signal files, that the user can recreated pretty easily..? I don't
think those really rise to the level of pg_wal.

What I would hope to see (... well, we know what I *really* would hope
to see, but if we really go this route) is something like:

WARNING: pg_wal not empty, WAL files are not validated by this tool
data files successfully verified

and a non-zero exit code.

Basically, if you're doing WAL yourself, then you'd use pg_receivewal
and maybe your own manifest-building code for WAL or something and then
use -X none with pg_basebackup.

Then again, I'd have -X none throw a warning too. I'd be alright with
all of these having override switches to say "ok, I get it, don't
complain about it".

I disagree with the idea of writing "backup successfully verified" when
we aren't doing any checking of the WAL that's essential for the backup
(unlike various signal files and whatnot, which aren't...).

Thanks,

Stephen