Document that expression indexes that call functions allow function-level

statistics.

diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index ecec84cc2d927bb83d5ad50e6937f0170d07c30c..0b01467ee018c7510ea0d2ab40c35559032e60d2 100644 (file)
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -1,4 +1,4 @@
-
+
 
 
  Routine Database Maintenance Tasks
@@ -318,6 +318,14 @@
      SET STATISTICS, or change the database-wide default using the 
      linkend="guc-default-statistics-target"> configuration parameter.
     
+
+    
+     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.
+