Re (1), I somehow managed to miss that sentence - thanks.

Re (2), let me put the question another way.

Given that it's going to close the connection every time, rather than
re-use it, if I'm wanting to do this hundreds or thousands of times from
within a single stored procedure call in database A, will the overhead
of reconnecting to database B hundreds or thousands of times mean that
using WITH AUTONOMOUS TRANSACTION is likely to be an impractical design
in performance terms? How many hundreds or thousands of times per second
can a connection be set up and torn down?

Sure I could set up a pair of servers, write some code, and measure the
performance. But I was hoping there might be someone who had used this
feature who might be able to give general advice along the lines of
either "no chance, you don't want to do it like that, it'll run like a
fast-asleep snail" or "we do that all the time, there's no performance
issue in practice, setting up the connection is a fraction of the cost
of running a statement that actually does anything".

--
Tim Ward