On Thu, 2 Jan 2003, Tom Lane wrote:
> "Michael Paesold" <mpaesold@gmx.at> writes:
> > Now setting autocommit=off the set transaction isolation level command does
> > not show any effect:
>
> > billing=# set autocommit to off;
> > SET
> > billing=# set transaction isolation level serializable;
> > SET
>
> SET does not start a transaction block, so this will not work. You must
> use an explicit BEGIN before setting TRANSACTION ISOLATION LEVEL.
>
> You might instead set default_transaction_isolation to get the behavior
> I think you are looking for.
The overall behavior appears to be against spec, but I figure this was
discussed at the time the set transation was added.