Not quite there... but almost. At some point in the life of the product my company has, we were having a real bottleneck in the DB. The solution was to "split

Not quite there... but almost. At some point in the life of the product my company has, we were having a real bottleneck in the DB. The solution was to "split" the data in different DBs, that would hold several clients. So, we could say we have the worst of both worlds (As code still has to deal with the "security" part). It is even more complicated, as some table exist only in the "main" db, and we fetch data from there constantly. So far (Probably 10+ years since we implemented this). We haven't had any real issue because of this, and we have developed small in house tools to keep things tidy (like schema updates or data inspection). Server is MySQL.