On Wed, Feb 23, 2011 at 12:50 AM, Nathan Boley <npbo...@gmail.com> wrote: >> Personally, I think the first thing we ought to do is add a real, bona >> fide planner hint to override the selectivity calculation manually, >> maybe something like this: >> >> WHERE (x < 5 AND y = 1) SELECTIVITY (0.1); > > If you're going to go that far, why not just collect statistics on > that specific predicate? > > ie, ANALYZE SELECTIVITY ON tablename (x, y) WHERE (x < 5 AND y = 1); > > Then it won't fall subject to all of the pitfalls that Tom outlines below. > > Selectivities are easy to estimate if we know the predicate. They only > become hard when they have to work for every possible predicate.
Fair point. -- 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
