linkend="wait-event-extension-table"/> and
     <xref linkend="wait-event-lwlock-table"/>. In some cases, the name
     of an <literal>LWLock</literal> assigned by an extension will not be
     available in all server processes.  It might be reported as just
     <quote><literal>extension</literal></quote> rather than the
     extension-assigned name.
    </para>
   </note>
 </sect2>

 <sect2 id="monitoring-pg-stat-replication-view">
  <title><structname>pg_stat_replication</structname></title>

  <indexterm>
   <primary>pg_stat_replication</primary>
  </indexterm>

   <para>
   The <structname>pg_stat_replication</structname> view will contain one row
   per WAL sender process, showing statistics about replication to that
   sender's connected standby server.  Only directly connected standbys are
   listed; no information is available about downstream standby servers.
  </para>

  <table id="pg-stat-replication-view" xreflabel="pg_stat_replication">
   <title><structname>pg_stat_replication</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of a WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesysid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the user logged into this WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
      </para>
      <para>
       Name of the user logged into this WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>application_name</structfield> <type>text</type>
      </para>
      <para>
       Name of the application that is connected
       to this WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_addr</structfield> <type>inet</type>
      </para>
      <para>
       IP address of the client connected to this WAL sender.
       If this field is null, it indicates that the client is
       connected via a Unix socket on the server machine.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_hostname</structfield> <type>text</type>
      </para>
      <para>
       Host name of the connected client, as reported by a
       reverse DNS lookup of <structfield>client_addr</structfield>. This field will
       only be non-null for IP connections, and only when <xref linkend="guc-log-hostname"/> is enabled.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_port</structfield> <type>integer</type>
      </para>
      <para>
       TCP port number that the client is using for communication
       with this WAL sender, or <literal>-1</literal> if a Unix socket is used
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_start</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time when this process was started, i.e., when the
       client connected to this WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_xmin</structfield>