Is there any particular reason why a backend has to be started by the
postmaster unless it is the only backend running (in debug mode) ?
I'm thinking here that
(a) It would be more convenient to debug if you didn't have to shut down
the postmaster to run gdb postgres and...
(b) If that were the case you be part-way to implementing a
single-process database option like some databases have.
What are the issues? Finding the shared memory etc perhaps?