Heikki Linnakangas <hlinnaka@iki.fi> writes:
> I also did some quick performance testing with a simple update designed
> as a worst-case scenario:
> vacuum tab; update tab set b = b, a = a;
> In this case, the patch fetches the old tuple, but it wouldn't really
> need to, because all the columns are updated. Could we optimize that
> special case?
I'm not following. We need to read the old values of a and b for
the update source expressions, no?
(One could imagine realizing that this is a no-op update, but that
seems quite distinct from the problem at hand, and probably not
worth the cycles.)
regards, tom lane