From: Sandro Santilli <strk@keybit.net>
Date: Tue, 14 Sep 2004 12:23:27 +0000 (+0000)
Subject: Added a note about tweeking random_page_cost
X-Git-Tag: pgis_1_0_0RC1~450
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=d40896fc14523a9c402acc73835c1c46b1729749;p=postgis

Added a note about tweeking random_page_cost


git-svn-id: http://svn.osgeo.org/postgis/trunk@819 b70326c6-7e19-0410-871a-916f4a2858ee
---

diff --git a/doc/postgis.xml b/doc/postgis.xml
index 362b43375..31147f6d2 100644
--- a/doc/postgis.xml
+++ b/doc/postgis.xml
@@ -1488,6 +1488,16 @@ SELECT UPDATE_GEOMETRY_STATS([table_name], [column_name]);</programlisting></par
               <varname>ENABLE_SEQSCAN</varname>.</para>
             </note>
           </listitem>
+
+          <listitem>
+            <para>If you find the planner wrong about the cost of
+	    sequencial vs index scans try reducing the value of
+	    random_page_cost in postgresql.conf or using SET
+	    random_page_cost=#. Default value for the parameter
+	    is 4, try setting it to 1 or 2. Decrementing the
+	    value makes the planner more inclined of using Index scans.
+            </para>
+          </listitem>
         </itemizedlist>
       </sect2>
     </sect1>