On Tue, Apr 25, 2017 at 04:03:53PM +1200, David Rowley wrote: > ..On 25 April 2017 at 13:31, Bruce Momjian <br...@momjian.us> wrote: > > The only unusual thing is that this release has ~180 items while most > > recent release have had ~220. The pattern I see that there are more > > large features in this release than previous ones. > > Thanks for drafting this up. > > I understand that it may have been filtered out, but I'd say that > 7e534adcdc70 is worth a mention. > > Users creating BRIN indexes previously would have had to know > beforehand that the table would be sufficiently correlated on the > indexed columns for the index to be worthwhile, whereas now there's a > lesser need for the user to know this beforehand.
I can't see how this can be added to an existing BRIN entry, so it would have to be new. The text would be: Improve accuracy in determining if a BRIN index scan is beneficial though this not something I would normally mention becuause most users don't understand the optimizer choices and just assume it works. > Also: > > <para> > New commands are <command><link linkend="SQL-CREATESTATISTICS">CREATE</></>, > <command><link linkend="SQL-ALTERSTATISTICS">ALTER</></>, and > <command><link linkend="SQL-DROPSTATISTICS">DROP STATISTICS</></>. > This is helpful in > estimating query memory usage and ... HOW IS RATIO USED? > </para> > > HOW IS RATIO USED? .... There are two types of new stats; > > ndistinct, which can improve row estimations in the query planner for > estimating the number of distinct value groups over multiple columns. Yes, I understood that one. > functionaldeps, which provides the planner with a better understanding > of functional depdenences between columns on which the statistics are > defined. The planner takes the functional dependency degree into > account when multiplying selectivity estimations for multiple columns. Ah, so it is used when combining estimates --- makes sense. New text: This is helpful in estimating query memory usage and when combining the statistics from individual columns. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers