On Wed, Oct 12, 2011 at 2:50 AM, Jeff Davis <pg...@j-davis.com> wrote: > On Tue, 2011-10-11 at 13:22 -0400, Robert Haas wrote: >> The real issue is that the costing estimates need to be accurate, and >> that's where the rubber hits the road. Otherwise, even if we pick the >> right way to scan the table, we may do silly things up the line when >> we go to start constructing the join order. I think we need to beef >> up ANALYZE to gather statistics on the fraction of the pages that are >> marked all-visible, or maybe VACUUM should gather that information. >> The trouble is that if we VACUUM and then ANALYZE, we'll often get >> back a value very close to 100%, but then the real value may diminish >> quite a bit before the next auto-analyze fires. I think if we can >> figure out what to do about that problem we'll be well on our way... > > Can you send stats messages to keep track when you unset a bit in the > VM? That might allow it to be more up-to-date.
In theory, that seems like it would work, although I'm a little worried about the overhead. -- 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
