by WhiteRider » Sun Oct 21, 2018 4:43 am
Databases created in one version of PostgreSQL cannot be used in another version so just updating PostgreSQL (without backing up & restoring your databases) would not work.
However there are technical differences in the way later/different PostgreSQL versions work - in theory the core functionality should be compatible, but there are subtle differences which I understand can cause problems in some rare cases. I don't know exactly what causes this, and you may find that it works perfectly well for you, but it's also possible that you may have problems further down the line or in ways that aren't immediately obvious.
Unless you have an extremely large database I think you're unlikely to see any significant improvement in performance, although I don't have any figures for that. Did you need to upgrade PostgreSQL for some other reason than PT4?