<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> <type>xid</type>
      </para>
      <para>
       This standby's <literal>xmin</literal> horizon reported
       by <xref linkend="guc-hot-standby-feedback"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>state</structfield> <type>text</type>
      </para>
      <para>
       Current WAL sender state.
       Possible values are:
       <itemizedlist>
        <listitem>
         <para>
          <literal>startup</literal>: This WAL sender is starting up.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>catchup</literal>: This WAL sender's connected standby is
          catching up with the primary.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>streaming</literal>: This WAL sender is streaming changes
          after its connected standby server has caught up with the primary.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>backup</literal>: This WAL sender is sending a backup.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>stopping</literal>: This WAL sender is stopping.
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sent_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location sent on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>write_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location written to disk by this standby
       server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>flush_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location flushed to disk by this standby
       server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>replay_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location replayed into the database on this
       standby server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>write_lag</structfield> <type>interval</type>
      </para>
      <para>
       Time elapsed between flushing recent WAL locally and receiving
       notification that this standby server has written it (but not yet
       flushed it or applied it).  This can be used to gauge the delay that
       <literal>synchronous_commit</literal> level
       <literal>remote_write</literal>