Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> The other possibility here is that this just doesn't work. :-)
That's why we wanted to test it ;-).
I don't have time to look right now, but ISTM the original discussion
that led to making that patch had ideas about scenarios where it would
be faster. It'd be worth digging that up and seeing if the current
tests covered the case or not.
regards, tom lane