result is the number of bytes separating
    those write-ahead log locations.  Also the number of bytes can be
    added into and subtracted from LSN using the
    <code class="literal">+(pg_lsn,numeric)</code> and
    <code class="literal">-(pg_lsn,numeric)</code> operators, respectively. Note that
    the calculated LSN should be in the range of <code class="type">pg_lsn</code> type,
    i.e., between <code class="literal">0/0</code> and
    <code class="literal">FFFFFFFF/FFFFFFFF</code>.
   </p></div><di