On Tue, Nov 30, 2010 at 12:10 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > 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,
True. > plus a WAL image of the heap page, so a False. That is exactly what we are NOT doing now and what we must find a way to avoid doing. > 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. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
