I thought if I had some application logic that needed a certain kind of transaction (maybe a non-default isolation level), I could hide that fact in a procedure. App code (Java/Python/whatever) could remain unaware of transactions (except maybe needing to retry after a failure) and simply send `call foo(?, ?)` to the DB. But maybe that kind of design is not supported, and application code needs to start transactions and set isolation levels. Is that accurate? I supposed a procedure could throw an exception if it doesn’t like the value in `current_setting('transaction_isolation’)`.
Also, I tried putting a `start transaction` command in the procedure. I got another error: `unsupported transaction command in PL/pgSQL`. Are procedures not allowed to start transactions? Or is there another command?