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.
