Make vacuum_defer_cleanup_age be PGC_SIGHUP level, since it's not sensible

to have different values in different processes of the primary server.
Also put it into the "Streaming Replication" GUC category; it doesn't belong
in "Standby Servers" because you use it on the master not the standby.
In passing also correct guc.c's idea of wal_keep_segments' category.

1 files changed, 26 insertions, 24 deletions

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 391e4365c0c..86bf6ee9121 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 1.289 2010/07/03 20:43:57 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.290 2010/07/03 21:23:58 tgl Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -1914,6 +1914,31 @@ SET ENABLE_SEQSCAN TO OFF;
        </para>
        </listitem>
       </varlistentry>
+
+     <varlistentry id="guc-vacuum-defer-cleanup-age" xreflabel="vacuum_defer_cleanup_age">
+      <term><varname>vacuum_defer_cleanup_age</varname> (<type>integer</type>)</term>
+      <indexterm>
+       <primary><varname>vacuum_defer_cleanup_age</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        Specifies the number of transactions by which <command>VACUUM</> and
+        <acronym>HOT</> updates will defer cleanup of dead row versions. The
+        default is zero transactions, meaning that dead row versions can be
+        removed as soon as possible, that is, as soon as they are no longer
+        visible to any open transaction.  You may wish to set this to a
+	non-zero value on a primary server that is supporting hot standby
+        servers, as described in <xref linkend="hot-standby">.  This allows
+        more time for queries on the standby to complete without incurring
+        conflicts due to early cleanup of rows.  However, since the value
+        is measured in terms of number of write transactions occurring on the
+        primary server, it is difficult to predict just how much additional
+        grace time will be made available to standby queries.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+       </para>
+      </listitem>
+     </varlistentry>
      </variablelist>
     </sect2>
 
@@ -2004,29 +2029,6 @@ SET ENABLE_SEQSCAN TO OFF;
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-vacuum-defer-cleanup-age" xreflabel="vacuum_defer_cleanup_age">
-      <term><varname>vacuum_defer_cleanup_age</varname> (<type>integer</type>)</term>
-      <indexterm>
-       <primary><varname>vacuum_defer_cleanup_age</> configuration parameter</primary>
-      </indexterm>
-      <listitem>
-       <para>
-        Specifies the number of transactions by which <command>VACUUM</> and
-        <acronym>HOT</> updates will defer cleanup of dead row versions. The
-        default is 0 transactions, meaning that dead row versions will be
-        removed as soon as possible. You may wish to set this to a non-zero
-        value when planning or maintaining a Hot Standby connection, as
-        described in <xref linkend="hot-standby">.  The recommended value is
-        <literal>0</> unless you have clear reason to increase it. The purpose
-        of the parameter is to allow the user to specify an approximate time
-        delay before cleanup occurs. However, it should be noted that there is
-        no direct link with any specific time delay and so the results will be
-        application and installation specific, as well as variable over time,
-        depending upon the transaction rate (of writes only).
-       </para>
-      </listitem>
-     </varlistentry>
-
      </variablelist>
     </sect2>
    </sect1>