it's not too bad, Grant. The presumption is that all tenants are using the same software and schema, just that every data row is tagged with a Tenant ID and every access has to be filtered based on it. the filtering can easily be made bulletproof through the use of a universal layer of Views, and (owner)Schema security that forces all access to the tables through those views. (Hmm, maybe I should write an article on this ...) 🙂

Anyway, (design)schema upgrades are only slightly more complicated than a single-tenant environment.