Is this zero-downtime? pg_upgrade with the link option is pretty fast, usually only taking a few minutes even with our >10TB database, but it does require taking the server down while it's running which is a major issue for many modern apps.

I'm loving the cockroachdb upgrade process for our cluster - you just do a zero-downtime rolling restart to the next major version, with the ability to roll back to the old version if you see issues, and then when ready allow the database to apply it's migrations internally to upgrade the data structures, which is also zero-downtime.