Re: pg_upgrade: can I use same binary for old & new?

On Sat, Jul 5, 2025 at 3:19 PM Pierre Fortin <pf(at)pfortin(dot)com> wrote:

> On Sat, 05 Jul 2025 14:30:20 -0400 Tom Lane wrote:
>
> Forgive my ignorance; always trying to learn more... :)
>
> >pf(at)pfortin(dot)com writes:
> >> On Sat, 5 Jul 2025 11:11:32 -0700 Adrian Klaver wrote:
> >>> How did you measure above?
> >
> >> # du -sb /var/lib/pgsql/data
> >> 8227910662297 /var/lib/pgsql/data
> >
> >It's likely that there's a deal of bloat in that. Even if there's not
> >much bloat, this number will include indexes and WAL data that don't
> >appear in pg_dump output.
>
> Does this imply that on restore, I'll have to re-index everything?
>
> >>> What was the pg_dump command?
> >
> >> Didn't try given:
> >> $ df /mnt/db
> >> Filesystem Size Used Avail Use% Mounted on
> >> /dev/sdh1 17T 13T 3.0T 82% /mnt/db
> >
> >I'd say give it a try; be sure to use one of the pg_dump modes
> >that compress the data.
>
> OK... I failed to mention I have several databases in this cluster; so
> digging into pg_dumpall, I see:
> --binary-upgrade
> This option is for use by in-place upgrade utilities. Its use for
> other purposes is not recommended or supported. The behavior of the
> option may change in future releases without notice.
>
> pg_upgrade has --link option; but I'm puzzled by this option in a
> dumpall/restore process.

It's _not_ part of a dumpall/restore process.

You _either_ run
- pg_upgrade --link
OR
- pg_dumpall --globals-only > globals.sql / psql -f globals.sql
- pg_dump --format=directory / pg_restore --format=directory of db1
- pg_dump --format=directory / pg_restore --format=directory of db2
- pg_dump --format=directory / pg_restore --format=directory of db3
- pg_dump --format=directory / pg_restore --format=directory of etc...

Why not a plain pg_dumpall of the whole instance? Because that would
create a GINORMOUS text file which can only be loaded in a single-threaded
manner.

> My imagination wonders if this alludes to a way
> to do something like:
> pg_dumpall --globals-only --roles-only --schema-only ...
> Would restoring this be a way to update only the control structures? Big
> assumption that the actual data remains untouched...
>
> Inquiring mind... :)
>
> Back to my upgrade issue...
> All my DBs are static (only queries once loaded). Assuming the dumpall
> file fits on one of my drives:
> pg_dumpall -f <path>/PG.backup -v
> appears to be all I need? pg_dump has compression by default; but I don't
> see compression with dumpall other than for TOAST.
>
> Thanks, You guys are awesome!
>
> > regards, tom lane
>
>
>

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