Add COST and ROWS options to CREATE/ALTER FUNCTION, plus underlying pg_proc

columns procost and prorows, to allow simple user adjustment of the estimated
cost of a function call, as well as control of the estimated number of rows
returned by a set-returning function.  We might eventually wish to extend this
to allow function-specific estimation routines, but there seems to be
consensus that we should try a simple constant estimate first.  In particular
this provides a relatively simple way to control the order in which different
WHERE clauses are applied in a plan node, which is a Good Thing in view of the
fact that the recent EquivalenceClass planner rewrite made that much less
predictable than before.

1 files changed, 27 insertions, 1 deletions

diff --git a/doc/src/sgml/ref/alter_function.sgml b/doc/src/sgml/ref/alter_function.sgml
index d56437538e9..150ca3d418f 100644
--- a/doc/src/sgml/ref/alter_function.sgml
+++ b/doc/src/sgml/ref/alter_function.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/alter_function.sgml,v 1.12 2006/09/16 00:30:16 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/alter_function.sgml,v 1.13 2007/01/22 01:35:19 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -34,6 +34,8 @@ where <replaceable class="PARAMETER">action</replaceable> is one of:
     CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     IMMUTABLE | STABLE | VOLATILE
     [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
+    COST <replaceable class="parameter">execution_cost</replaceable>
+    ROWS <replaceable class="parameter">result_rows</replaceable>
 </synopsis>
  </refsynopsisdiv>
   
@@ -186,6 +188,30 @@ where <replaceable class="PARAMETER">action</replaceable> is one of:
     </listitem>
    </varlistentry>
 
+    <varlistentry>
+     <term><literal>COST</literal> <replaceable class="parameter">execution_cost</replaceable></term>
+
+     <listitem>
+      <para>
+       Change the estimated execution cost of the function.
+       See <xref linkend="sql-createfunction"
+       endterm="sql-createfunction-title"> for more information.
+      </para>
+     </listitem>
+   </varlistentry>
+
+    <varlistentry>
+     <term><literal>ROWS</literal> <replaceable class="parameter">result_rows</replaceable></term>
+
+     <listitem>
+      <para>
+       Change the estimated number of rows returned by a set-returning
+       function.  See <xref linkend="sql-createfunction"
+       endterm="sql-createfunction-title"> for more information.
+      </para>
+     </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>RESTRICT</literal></term>