From db147b348345288c7b47f9527fc107a9bb063ad7 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 2 May 2008 21:26:10 +0000
Subject: Allow the planner's estimate of the fraction of a cursor's rows that
 will be retrieved to be controlled through a GUC variable.

Robert Hell
---
 doc/src/sgml/config.sgml | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 1e1e069a411..a3fecc4934c 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.176 2008/05/01 19:55:40 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.177 2008/05/02 21:26:09 tgl Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -2238,6 +2238,26 @@ SELECT * FROM parent WHERE key = 2400;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-cursor-tuple-fraction" xreflabel="cursor_tuple_fraction">
+      <term><varname>cursor_tuple_fraction</varname> (<type>floating point</type>)</term>
+      <indexterm>
+       <primary><varname>cursor_tuple_fraction</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        Sets the planner's estimate of the fraction of a cursor's rows that
+        will be retrieved.  The default is 0.1.  Smaller values of this
+        setting bias the planner towards using <quote>fast start</> plans
+        for cursors, which will retrieve the first few rows quickly while
+        perhaps taking a long time to fetch all rows.  Larger values
+        put more emphasis on the total estimated time.  At the maximum
+        setting of 1.0, cursors are planned exactly like regular queries,
+        considering only the total estimated time and not how soon the
+        first rows might be delivered.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-from-collapse-limit" xreflabel="from_collapse_limit">
       <term><varname>from_collapse_limit</varname> (<type>integer</type>)</term>
       <indexterm>
-- 
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