postgres.git / summary / log / commit / refs

commit    337020798674bcdfefe93e2277d98458da7266cd
Author:   Bruce Momjian <bruce@momjian.us>
Date:     Thu Nov 12 20:00:44 2020 +0000
First released in: 14.0, 9.5.25, 9.6.21, 10.16, 11.11, 12.6, 13.2

    docs: mention that expression indexes need analyze
    
    Expression indexes can't benefit from pre-computed statistics on
    columns.
    
    Reported-by: Nikolay Samokhvalov
    
    Discussion: https://postgr.es/m/CANNMO++5rw9RDA=p40iMVbMNPaW6O=S0AFzTU=KpYHRpCd1voA@mail.gmail.com
    
    Author: Nikolay Samokhvalov, modified
    
    Backpatch-through: 9.5


 doc/src/sgml/ref/create_index.sgml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 749db2845e8..844f00904be 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -745,6 +745,16 @@ Indexes:
    sort high</quote>, in queries that depend on indexes to avoid sorting steps.
   </para>
 
+  <para>
+   The regularly system 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 about new expression indexes.
+  </para>
+
   <para>
    For most index methods, the speed of creating an index is
    dependent on the setting of <xref linkend="guc-maintenance-work-mem"/>.


[parent: 66a8f090485e]