HOW TO CHECK WHETHER PHYSICAL STANDBY IS IN SYNC WITH THE PRIMARY OR NOT AND RESOLVED GAP ?


Step by Step Process to Resolved gap on Standby database.

Summary
1. Check the name and status of database.
2. Check for GAP on standby
3. Check redo received on standby
4. Check redo applied on standby
5. Identify missing archive log files
6. Copy archive log files
7. Register archive log files with standby
8. Restart the managed recovery operations

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Step 1 : Check the status of database on both server.
On Primary Server.
SQL> select name, open_mode, database_role from v$database;
NAME      OPEN_MODE  DATABASE_ROLE
——— ———- —————-
MYDB   READ WRITE PRIMARY

SQL> set sqlprompt “PRIMARY’@’_connect_identifier>”
PRIMARY@MYDB>

On Standby Server.

SQL> select name, open_mode, database_role from v$database;
NAME      OPEN_MODE  DATABASE_ROLE
——— ———- —————-
MYDB   MOUNTED    PHYSICAL STANDBY

SQL> set sqlprompt “SECONDARY’@’_connect_identifier>”
STANDBY@MYDB>

Step 2 : Check for GAP on Standby
PRIMARY@MYDB>select max(sequence#) from v$log_history;

MAX(SEQUENCE#)
————–
         76921
STANDBY@MYDB>select max(sequence#) from v$log_history;
MAX(SEQUENCE#)
————–
         76921

STANDBY@MYDB>SELECT THREAD# “Thread”,SEQUENCE# “Last Sequence Generated”
 FROM V$ARCHIVED_LOG
          WHERE (THREAD#,FIRST_TIME ) IN (SELECT THREAD#,MAX(FIRST_TIME) FROM V$ARCHIVED_LOG GROUP BY THREAD#)
          ORDER BY 1;
    Thread Last Sequence Generated
———- ———————–
         1                   76921



Step 3 & 4: Check redo received and applied on standby.

STANDBY@MYDB> SELECT ARCH.THREAD# “Thread”, ARCH.SEQUENCE# “Last Sequence Received”,
APPL.SEQUENCE# “Last Sequence Applied”, (ARCH.SEQUENCE# – APPL.SEQUENCE#) “Difference”
FROM
(SELECT THREAD# ,SEQUENCE# FROM V$ARCHIVED_LOG WHERE (THREAD#,FIRST_TIME ) IN
(SELECT THREAD#,MAX(FIRST_TIME) FROM V$ARCHIVED_LOG GROUP BY THREAD#)) ARCH,
(SELECT THREAD# ,SEQUENCE# FROM V$LOG_HISTORY WHERE (THREAD#,FIRST_TIME ) IN
(SELECT THREAD#,MAX(FIRST_TIME) FROM V$LOG_HISTORY GROUP BY THREAD#)) APPL
WHERE
ARCH.THREAD# = APPL.THREAD#
ORDER BY 1;
    Thread Last Sequence Received Last Sequence Applied Difference
———- ———————- ——————— ———-
         1                  76922                 20931      55991

Step 5: Identify the missing archive log file.

 STANDBY@MYDB>SELECT THREAD#, LOW_SEQUENCE#, HIGH_SEQUENCE# FROM V$ARCHIVE_GAP;
no rows selected

—-If found gap

Step 6: Copy missing archive log file
After identifying a gap (as shown above), the DBA will need to query the primary database to locate the archived redo logs on the primary database. The following query assumes the local archive destination on the primary database is LOG_ARCHIVE_DEST_1:
PRIMARY@MYDB>  SELECT name
 FROM v$archived_log
 WHERE thread# = 1
 AND dest_id = 1
 AND sequence# BETWEEN 20931 and 76922;
Output:
/oracle/bases/MYDB/archives/MYDB_0001_0716381751_0000076922.arc
56027 rows selected.

Step 7: Register archive logfile with standby.
Copy the above redo log files to the physical standby database and register them using the ALTER DATABASE REGISTER LOGFILE … SQL statement on the physical standby database.
For example:
STANDBY@MYDB> ALTER DATABASE REGISTER LOGFILE ‘/oracle/bases/MYDB/archives/MYDB_0001_0716381751_0000076922.arc’;

Step 8: Restart the managed recovery operations.
— After the redo logs have been registered on the physical standby database, the DBA can restart the managed recovery operations.
  For example, to put the physical standby database into automatic recovery managed mode:
STANDBY@MYDB> alter database recover managed standby database disconnect from session;