Data Guard Status

Standby - Difference between SCN Timestamp and SYSTIMESTAMP of DB instance

SELECT TO_CHAR(SCN_TO_TIMESTAMP(CURRENT_SCN), 'DD-MON-YYYY HH24:MI SSxFF') as LAST_COMMIT_TIME, 
TO_CHAR(SYSTIMESTAMP, 'DD-MON-YYYY HH24:MI SSxFF') as CURRENT_DB_TIME 
FROM V$DATABASE;

Standby - Seconds Between SCN Timestamp and SYSTIMESTAMP of DB instance

SELECT TO_CHAR(SYSDATE,'YYYY-MM-DD HH24:MI'), 
       INST_ID, 
       ( CAST( SYSTIMESTAMP AS DATE ) - CAST( SCN_TO_TIMESTAMP(CURRENT_SCN) AS DATE ) ) * 86400 AS SECONDS_LAG
FROM GV$DATABASE; 

Standby - Log Apply Status by Thread

SELECT a.thread#, 
       b. last_seq, a.applied_seq, 
       TO_CHAR(a. last_app_timestamp,'YYYY-MM-DD HH24:MI') LAST_APP_TIMESTAMP, 
       b.last_seq-a.applied_seq   ARC_DIFF 
  FROM (SELECT thread#, 
               MAX(sequence#) applied_seq, 
               MAX(next_time) last_app_timestamp 
          FROM gv$archived_log 
         WHERE applied = 'YES' GROUP BY thread#) a,  
       (SELECT thread#, 
               MAX (sequence#) last_seq 
          FROM gv$archived_log 
         GROUP BY thread#) b 
 WHERE a.thread# = b.thread#;