Excerpts from Tom Lane's message of lun feb 21 21:00:19 -0300 2011:
> Alvaro Herrera <alvhe...@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.

That's true too.  So let's discuss the syntax.  Maybe
        START TRANSACTION SNAPSHOT '\xdeadbeef';

This kind of extension seems ugly though; maybe we should consider
        START TRANSACTION (snapshot='\xdeadbeef');
(like VACUUM, EXPLAIN and COPY) or some such?

I don't think we need another "top-level" command for this.

Álvaro Herrera <alvhe...@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
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