Add a SHOW command to the replication command language.

This is useful infrastructure for an upcoming proposed patch to
allow the WAL segment size to be changed at initdb time; tools like
pg_basebackup need the ability to interrogate the server setting.
But it also doesn't seem like a bad thing to have independently of
that; it may find other uses in the future.

Robert Haas and Beena Emerson.  (The original patch here was by
Beena, but I rewrote it to such a degree that most of the code
being committed here is mine.)

Discussion: http://postgr.es/m/CA+TgmobNo4qz06wHEmy9DszAre3dYx-WNhHSCbU9SAwf+9Ft6g@mail.gmail.com

1 files changed, 24 insertions, 0 deletions

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 5f89db58570..028ef10d91b 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1394,6 +1394,30 @@ The commands accepted in walsender mode are:
   </varlistentry>
 
   <varlistentry>
+    <term><literal>SHOW</literal> <replaceable class="parameter">name</replaceable>
+     <indexterm><primary>SHOW</primary></indexterm>
+    </term>
+    <listitem>
+     <para>
+      Requests the server to send the current setting of a run-time parameter.
+      This is similar to the SQL command <xref linkend="sql-show">.
+     </para>
+
+     <variablelist>
+      <varlistentry>
+       <term><replaceable class="parameter">name</></term>
+       <listitem>
+         <para>
+          The name of a run-time parameter. Available parameters are documented
+          in <xref linkend="runtime-config">.
+         </para>
+       </listitem>
+      </varlistentry>
+     </variablelist>
+    </listitem>
+  </varlistentry>
+
+  <varlistentry>
     <term><literal>TIMELINE_HISTORY</literal> <replaceable class="parameter">tli</replaceable>
      <indexterm><primary>TIMELINE_HISTORY</primary></indexterm>
     </term>