Stonebraker isn't entirely impartial here as he's trying to sell his own product in this area (VoltDB) which is highly dependent on the "database-side logic" approach.Well, the quote is old, and the db he was trying to sell at the time was Informix, but I suppose that's a fair bit of truth to that. It is worth noting however, that he suggests in that paper that RDBMS and ORDBMS engines operate in different markets.
There's an important tradeoff being discussed here, which is, "can we get directly the data we want from the query", versus, "do we need to load all the data into our app first and filter it there". This is of course the critical thing that a lot more people need to learn, and the work I do with SQLAlchemy is all about this. But in the SQLA approach, we use Python constructs on the app side which expand into SQL functions when rendered in a query. The effect is very similar to that which I see in most of the examples in your posts.
The only reason we do what we do in Postgres is because we want to support multiple programming languages with minimal work. It is a matter of having this be an API accessible to multiple tools where some may be written in Perl, some in Python, some in Perl, and some in Java. If you are just writing a single app and don't want that portability, yeah, it is the wrong approach.
Keeping SQL functions as app-side constructs has the advantage of source code management. It's easier to support multiple kinds of backends (I run against PG and SQL Server a lot) since you aren't tied to a stored procedure language.
Right. There's a huge tradeoff here between "one database with logic centralized for many apps" and "one app that runs on many databases." I am not convinced you can do both gracefully.
The big namespacing problems I see are, what if two different kinds of "classes" want to have the same method name ?
Yeah, we struggled with that, which is one reason why we are using input types to construct classes. Function overloading then solves the problem.
save(asset_item) and save(journal_entry) then both work and can be discovered as needed from the system catalogs.
I am not saying this is the right approach always. I am saying it is an approach which trades away the ideal of "one app on multiple databases" for the ideal of "one database for many apps."
Choose the right tool based on what you are doing.