On 22/12/2020 22:01, John Naylor wrote:
In 0004, it seems you have some doubts about upgrade compatibility. Is that because user-defined conversions would no longer have the right signature?
Exactly. If you have an extension that adds a custom conversion function and does CREATE CONVERSION, the old installation script will fail on the new version. That causes trouble for pg_dump+restore and pg_upgrade.
Perhaps we could accept the old signature in the server when you do CREATE CONVERSION, but somehow mark the conversion as broken in the catalog so that you would get a runtime error if you tried to use it. That would be enough to make pg_dump+restore (and pg_upgrade) not throw an error, and you could then upgrade the extension later (ALTER EXTENSION UPDATE).
I'm not sure it's worth the trouble, though. Custom conversions are very rare. And I don't think any other object can depend on a conversion, so you can always drop the conversion before upgrade, and re-create it with the new function signature afterwards. A note in the release notes and a check in pg_upgrade, with instructions to drop and recreate the conversion, are probably enough.
- Heikki
