Alvaro Herrera <alvherre@commandprompt.com> writes:
> Actually this seems rather difficult to do, because in order to invoke
> the function that imports the snapshot, you have to call SELECT, which
> acquires a snapshot beforehand. So when we actually import the
> passed-in snapshot, there's already a snapshot set. This is odious but
> I don't see a way around that -- other than adding special grammar
> support which seems overkill.
No, I don't think it is. The alternative is semantics that are
at least exceedingly ugly, and very possibly flat-out broken.
To take just one point, you have no way at all of preventing the
transaction from having done something else using its original
snapshot.
regards, tom lane