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 +

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