Re: backup manifests

On Fri, Mar 27, 2020 at 4:02 PM David Steele <david(at)pgmasters(dot)net> wrote:
> I prefer to validate the size and checksum in the same pass, but I'm not
> sure it's that big a deal. If the backup is being corrupted under the
> validate process that would also apply to files that had already been
> validated.

I did it like this because I thought that in typical scenarios it
would be likely to produce useful results more quickly. For instance,
suppose that you forget to restore the tablespace directories, and
just get the main $PGDATA directory. Well, if you do it all in one
pass, you might spend a long time checksumming things before you
realize that some files are completely missing. I thought it would be
useful to complain about files that are extra or missing or the wrong
size FIRST, because that only requires us to stat() each file, and
only after that do the comparatively extensive checksumming step that
requires us to read the entire contents of each file. Granted, unless
you use --exit-on-error, you're going to get all the complaints
eventually anyway, but you might use that option, or you might hit ^C
when you start to see a slough of complaints poppoing out.

Maybe that was the wrong idea, but I thought people would like the
idea of running cheaper checks first. I wasn't worried about
concurrent modification of the backup because then you're super-hosed
no matter what.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company