Re: Lifespan of a BeginInternalSubTransaction subxact ?

Chapman Flack <chap(at)anastigmatix(dot)net> writes:
> PL/Java implements JDBC Savepoints using BeginInternalSubTransaction/
> ReleaseCurrentSubTransaction/RollbackAndReleaseCurrentSubTransaction.
> That seems to be the Accepted Way of Doing Things within backend PLs
> that want control over error recovery, am I right?

Sounds about right, though I haven't checked the details exactly.

> PL/Java also strictly enforces that such a subxact set within a Java
> function must be released or rolled back by the time that function
> returns.

Yup.

> The reasoning there is less obvious to me; my intuition would have been
> that a subtransaction could remain in play for the life of its containing
> transaction, which could have been started outside of this Java function;

When control returns from a function, we resume executing the statement
that called it. This can *not* be in a different (sub)transaction than
the statement started in; that wouldn't make any sense logically, and
it certainly won't work from an implementation standpoint either.

The rules are laxer for procedures, I believe; at the very least those are
allowed to commit the calling transaction and start a new one. I'm less
sure about how they can interact with subtransactions. To support this,
a CALL statement has to not have any internal state that persists past
the procedure call. But a function cannot expect that the calling
statement lacks internal state.

regards, tom lane