"Jim C. Nasby" <jnasby@pervasive.com> writes:
> ISTM that as soon as vacuum dirties a page, it might as well update all
> tuples it can (any where Xmin < GetOldestXmin()), since that won't take
> much time compared to the cost of writing the page out.
Perhaps not, but what it will do is destroy data that you might wish you
had later. Check the archives and note how often we ask people for xmin
values when trying to debug a problem. I don't think it's a good idea
for aggressive freezing of tuples to be the default behavior. Moreover,
I can't see that there'd be any real gain from having done it --- it
doesn't look to me like it would save any vacuum-to-prevent-wraparound
operations, since nothing would happen at non-dirty pages.
regards, tom lane