Time for action – verifying synchronization between the primary and standby databases

By using the following steps, you can control whether the standby database is synchronized with primary:

1. On the standby database, query the V$ARCHIVED_LOG view for the archived and applied sequences.

   For the last archived sequence, use the following:

   SQL> SELECT MAX(SEQUENCE#) FROM V$ARCHIVED_LOG;
   MAX(SEQUENCE#)
   --------------
              145
   

   For the last applied sequence, use the following:

   SQL> SELECT MAX(SEQUENCE#) FROM V$ARCHIVED_LOG WHERE APPLIED='YES';
   MAX(SEQUENCE#)
   --------------
              144
   

   From the preceding two queries, we see that the latest sequence, 145, is being archived or written into the standby redo logfiles. There's expected to be a lag of one sequence between archived and applied columns.

2. Check the status of the latest log sequence.

   SQL> SELECT SEQUENCE#,APPLIED FROM V$ARCHIVED_LOG ORDER BY SEQUENCE#;
   
    SEQUENCE# APPLIED
   ---------- ---------
          140 YES
          141 YES
     ...