Hannu Krosing <hannu(at)tm(dot)ee> writes:
> But could we not make it so that rollback will also reset xmax and cmax
> to 0.
We never have done that and I don't see why we should start.
(And no, I'm not sure that it'd be entirely safe; there are
concurrency/atomicity issues involved, because we do not
insist on getting exclusive lock to set the it's-dead-Jim
flag bit.)
We could make the user readout of xmax/cmax be zeroes if the flag
bits show they are invalid. But this really just begs the question
of what use they are to users in the first place. I can't see any;
and if we make them read as zeroes then they for sure won't have any.
regards, tom lane