A good approach for this is to use pg_upgrade in-place, which should give you a downtime of a few minutes at most. (I have 800GB at work and would expect 1-2 m

A good approach for this is to use pg_upgrade in-place, which should give you a downtime of a few minutes at most. (I have 800GB at work and would expect 1-2 minutes for this.) I recommend installing PG12 on a temporary VM, duplicating the existing database, and test the upgrade in isolation. https://www.postgresql.org/docs/current/pgupgrade.html https://www.postgresql.org/docs/current/pgupgrade.html A more complicated approach uses replication, and upgrades the standby server before promoting it to the primary server.