Robert Haas <robertmh...@gmail.com> writes: > We're not going to double the cost of VACUUM to get index-only scans. > And that's exactly what will happen if you do full-page writes of > every heap page to set a single bit.
It's ridiculous to claim that that "doubles the cost of VACUUM". In the worst case, it will add 25% to the cost of setting an all-visible bit on a page where there is no other work to do. (You already are writing out the heap page and the VM page, plus a WAL image of the heap page, so a WAL image of the VM page adds 25%. But only if you did not set any other bits on the same VM page, which is probably not a real common case.) Given that VACUUM has a lot of other cleanup besides visibility bit setting, I'm not convinced that this would even be noticeable. I think the burden is on people who are proposing complicated mechanisms to show that there's actually a strong need for them. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers