Re: pg_basebackup, manifests and backends older than ~12

At Mon, 13 Apr 2020 09:56:02 +0900, Michael Paquier <michael(at)paquier(dot)xyz> wrote in
> On Sun, Apr 12, 2020 at 08:08:17AM +0900, Michael Paquier wrote:
> > Exactly. My point is exactly that. The current code would force
> > users maintaining scripts with pg_basebackup to use --no-manifest if
> > such a script runs with older versions of Postgres, but we should
> > encourage users not do to that because we want them to use manifests
> > with backend versions where they are supported.
>
> Please note that I have added an open item for this thread, and
> attached is a proposal of patch. While reading the code, I have
> noticed that the minimum version handling is not consistent with the
> other MINIMUM_VERSION_*, so I have added one for manifests.

Since I'm not sure about the work flow that contains taking a
basebackup from a server of a different version, I'm not sure which is
better between silently disabling and erroring out. However, it seems
to me, the option for replication slot is a choice of the way the tool
works which doesn't affect the result itself, but that for backup
manifest is about what the resulting backup contains. Therefore I
think it is better that pg_basebackup in PG13 should error out if the
source server doesn't support backup manifest but --no-manifest is not
specfied, and show how to accomplish their wants (, though I don't see
the wants clearly).

$ pg_basebackup ...
pg_basebackup: error: backup manifest is available from servers running PostgreSQL 13 or later
Try --no-manifest to take a backup from this server.

By the way, if I specified --manifest-checksums, it complains about
incompatible options with a message that would look strange to the
user.

pg_basebackup: error: --no-manifest and --manifest-checksums are incompatible options

("I didn't specified such an option..")

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center