Re: Downgrade pgsql 17 to pgsql 12 question

Thank you, Laurenz.

Yes, I say binary dump/restore would be faster because of the -j option.

Well, I suppose there's no certainty of what might break without going
through the whole process.

On Fri, Sep 26, 2025 at 7:57 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
wrote:

> On Fri, 2025-09-26 at 17:48 +0530, Ashish Mukherjee wrote:
> > I have a strange requirement to downgrade from pgsql 17 to pgsql 12.
> This is
> > because we found in production certain incompatibilities between both
> versions
> > for our database. It should have been caught in testing but was not.
> >
> > The clean way seems to be text file dump and restore but this would be
> too
> > huge and too slow for our database of 3T. If I use pg_dump v17 and then
> > restore with pg_restore v 17 on a pgsql v12 database, is there any risk?
>
> Yes, there is the risk that the restore will fail.
> Downgrading is not supported.
>
> That's why the best way to do it is a plain format dump: you can edit the
> dump file to manually fix any errors.
> I am surprised that you think that restoring a plain format dump would
> be significantly slower than restoring a different format (unless you are
> talking about parallel restore with -j).
>
> > I tried a small test with a bunch of tables and it worked, but am
> wondering
> > about the pitfalls. I am restoring from the directory format dump.
>
> Anything can happen...
>
> > When I do dump/restore like this for a test table, I get the following
> errors
> > during restore but the table gets restored fine.
> >
> > pg_restore: error: while PROCESSING TOC:
> > error: pg_restore: error: pg_restore: from TOC entry 17168; 1259
> 58572315 TABLE pkgs s14
> > pg_restore: error: pg_restore: pg_restore: pg_restore: from TOC entry
> 17168; 1259 58572315 TABLE pkgs s14
> > pg_restore: error: pg_restore: from TOC entry 17168; 1259 58572315
> TABLE pkgs s14
> > pg_restore: error: pg_restore: from TOC entry 17168; 1259 58572315 TABLE
> pkgs s14
> > error: from TOC entry 17168; 1259 58572315 TABLE pkgs s14
> > pg_restore: warning: errors ignored on restore: 2
> >
> > pkgs is the table and s14 is my database
>
> There should be more: the actual error messages. These will give you a
> clue.
>
> Yours,
> Laurenz Albe
>