On Tue, Apr 25, 2017 at 04:03:53PM +1200, David Rowley wrote:
> ..On 25 April 2017 at 13:31, Bruce Momjian <bruce@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 combiningthe statistics from individual columns.
-- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB
http://enterprisedb.com
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