I’m not familiar with what hoops extensions jump through to facilitate upgrades but even if it was as simple as “create extension upgrade” I wouldn’t have pg_upgrade execute that command (or at least not by default). I would maybe have pg_upgrade help move the libraries over from the old server (and we must be dealing with different databases having different extension versions in some manner…).
Well IMHO the status quo is terrible. Perhaps you have a suggestion on how to make it better ?
To a certain extent it is beyond pg_upgrade's purview to care about extension explicitly - it considers them "data" on the database side and copies over the schema and, within reason, punts on the filesystem by saying "ensure that the existing versions of your extensions in the old cluster can correctly run in the new cluster" (which basically just takes a simple file copy/install and the assumption you are upgrading to a server version that is supported by the extension in question - also a reasonable requirement). In short, I don't have a suggestion on how to improve that and don't really consider it a terrible flaw in pg_upgrade.
I'll readily admit that I lack sufficient knowledge here to make such suggestions as I don't hold any optionions that things are "quite terrible" and haven't been presented with concrete problems to consider alternatives for.
