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Date: Wed, 28 Jul 2021 21:03:08 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Nikolay Samokhvalov <samokhvalov@gmail.com>,
	PostgreSQL-documentation <pgsql-docs@postgresql.org>
Subject: Re: Indexes on Expressions - a note to remind users to run ANALYZE
 after creation
Message-ID: <20210729010308.GB9600@momjian.us>
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On Mon, Jul 19, 2021 at 12:59:10PM +0200, Laurenz Albe wrote:
> On Fri, 2021-07-16 at 22:00 -0700, Nikolay Samokhvalov wrote:
> > diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml
> > index 671299ff059d972ff95bdb1d67ed4c89bf5040b2..c7eaf9a608e995ef9957b4e0f677b36a8303be55 100644
> > --- a/doc/src/sgml/indices.sgml
> > +++ b/doc/src/sgml/indices.sgml
> > @@ -741,6 +741,15 @@ CREATE INDEX people_names ON people ((first_name || ' ' || last_name));
> >     query.  Thus, indexes on expressions are useful when retrieval speed
> >     is more important than insertion and update speed.
> >    </para>
> > +
> > +  <note>
> > +   <title>Note</title>
> > +   <para>
> > +    Once an index on an expression is successfully created, it is important to
> > +    run <literal>ANALYZE</literal> on the corresponding table to gather
> > +    statistics for the expression.
> > +   </para>
> > +  </note>
> >   </sect1>
> 
> I agree in principle.  It should be "has been created" rather than "is created",
> and I would say something less drastic like "usually a good idea" rather than
> "important".

Uh, CREATE INDEX already has this mentioend:

   The system regularly collects statistics on all of a table's
   columns.  Newly-created non-expression indexes can immediately
   use these statistics to determine an index's usefulness.
   For new expression indexes, it is necessary to run <link
   linkend="sql-analyze"><command>ANALYZE</command></link> or wait for
   the <link linkend="autovacuum">autovacuum daemon</link> to analyze
   the table to generate statistics for these indexes.

Do we need it here too?

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.