Index: doc/src/sgml/maintenance.sgml
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RCS file: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v
retrieving revision 1.99
diff -c -c -r1.99 maintenance.sgml
*** doc/src/sgml/maintenance.sgml	8 Feb 2010 04:33:51 -0000	1.99
--- doc/src/sgml/maintenance.sgml	23 Feb 2010 02:46:21 -0000
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       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>