Script to monitor data guard log shipping

SET PAGESIZE 124
COL DB_NAME FORMAT A8
COL HOSTNAME FORMAT A12
COL LOG_ARCHIVED FORMAT 999999
COL LOG_APPLIED FORMAT 999999
COL LOG_GAP FORMAT 9999
COL APPLIED_TIME FORMAT A12

SELECT DB_NAME,
       HOSTNAME,
       LOG_ARCHIVED,
       LOG_APPLIED,
       APPLIED_TIME,
       LOG_ARCHIVED - LOG_APPLIED LOG_GAP
  FROM (SELECT NAME DB_NAME FROM V$DATABASE),
       (SELECT UPPER (
                  SUBSTR (
                     HOST_NAME,
                     1,
                     (DECODE (INSTR (HOST_NAME, '.'),
                              0, LENGTH (HOST_NAME),
                              (INSTR (HOST_NAME, '.') - 1)))))
                  HOSTNAME
          FROM V$INSTANCE),
       (SELECT MAX (SEQUENCE#) LOG_ARCHIVED
          FROM V$ARCHIVED_LOG
         WHERE DEST_ID = 1 AND ARCHIVED = 'YES'),
       (SELECT MAX (SEQUENCE#) LOG_APPLIED
          FROM V$ARCHIVED_LOG
         WHERE DEST_ID = 2 AND APPLIED = 'YES'),
       (SELECT TO_CHAR (MAX (COMPLETION_TIME), 'DD-MON/HH24:MI') APPLIED_TIME
          FROM V$ARCHIVED_LOG
         WHERE DEST_ID = 2 AND APPLIED = 'YES');