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Document that expression indexes that call functions allow function-level

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statistics.
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Bruce Momjian 2010-02-23 02:47:27 +00:00
parent 7cdadc62ea
commit 1379fb052f
1 changed files with 9 additions and 1 deletions
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doc/src/sgml/maintenance.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.99 2010/02/08 04:33:51 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.100 2010/02/23 02:47:27 momjian Exp $ -->
<chapter id="maintenance">
<title>Routine Database Maintenance Tasks</title>
@ -318,6 +318,14 @@
SET STATISTICS</>, or change the database-wide default using the <xref
linkend="guc-default-statistics-target"> configuration parameter.
</para>
<para>
Also, by default there is limited information available about
the selectivity of functions. However, if you create an expression
index that uses a function call, useful statistics will be
gathered about the function, which can greatly improve query
plans that use the expression index.
</para>
</tip>
</sect2>