PostgreSQL replication connections as well as tools such as
       <application>pg_basebackup</application> use internally, but it can
       also be used by third-party applications.  For a description of the
       replication protocol, consult <xref linkend="protocol-replication"/>.
      </para>

      <para>
       The following values, which are case-insensitive, are supported:
       <variablelist>
        <varlistentry>
         <term>
          <literal>true</literal>, <literal>on</literal>,
          <literal>yes</literal>, <literal>1</literal>
         </term>
         <listitem>
          <para>
           The connection goes into physical replication mode.
          </para>
         </listitem>
        </varlistentry>

        <varlistentry>
         <term><literal>database</literal></term>
         <listitem>
          <para>
           The connection goes into logical replication mode, connecting to
           the database specified in the <literal>dbname</literal> parameter.
          </para>
         </listitem>
        </varlistentry>

        <varlistentry>
         <term>
          <literal>false</literal>, <literal>off</literal>,
          <literal>no</literal>, <literal>0</literal>
         </term>
         <listitem>
          <para>
           The connection is a regular one, which is the default behavior.
          </para>
         </listitem>
        </varlistentry>
       </variablelist>
      </para>

      <para>
       In physical or logical replication mode, only the simple query protocol
       can be used.
      </para>
      </listitem>
     </varlistentry>

     <varlistentry id="libpq-connect-gssencmode" xreflabel="gssencmode">
      <term><literal>gssencmode</literal></term>
      <listitem>
       <para>
        This option determines whether or with what priority a secure
        <acronym>GSS</acronym> TCP/IP connection will be negotiated with the
        server. There are three modes:

        <variablelist>
         <varlistentry>
          <term><literal>disable</literal></term>
          <listitem>
           <para>
            only try a non-<acronym>GSSAPI</acronym>-encrypted connection
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>prefer</literal> (default)</term>
          <listitem>
           <para>
            if there are <acronym>GSSAPI</acronym> credentials present (i.e.,
            in a credentials cache), first try
            a <acronym>GSSAPI</acronym>-encrypted connection; if that fails or
            there are no credentials, try a
            non-<acronym>GSSAPI</acronym>-encrypted connection.  This is the
            default when <productname>PostgreSQL</productname> has been
            compiled with <acronym>GSSAPI</acronym> support.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>require</literal></term>
          <listitem>
           <para>
            only try a <acronym>GSSAPI</acronym>-encrypted connection
           </para>
          </listitem>
         </varlistentry>
        </variablelist>
       </para>

       <para>
        <literal>gssencmode</literal> is ignored for Unix domain socket
        communication.  If <productname>PostgreSQL</productname> is compiled
        without GSSAPI support, using the <literal>require</literal> option
        will cause an error, while <literal>prefer</literal> will be accepted
        but <application>libpq</application> will not actually attempt
        a <acronym>GSSAPI</acronym>-encrypted
        connection.<indexterm><primary>GSSAPI</primary><secondary sortas="libpq">with
        libpq</secondary></indexterm>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="libpq-connect-sslmode" xreflabel="sslmode">
      <term><literal>sslmode</literal></term>
      <listitem>
       <para>
        This option determines whether or with what priority a secure