ORA-16416: No viable Physical Standby switchover targets available

You will see this error when you are trying to switchover from Primary to Standby, you will see the error when log_archive_dest_n not ready at standby or there is some issue with REDO log.

Also note that you will see this error if f there is an archive gap, that prevents switchover because of which the operation fails

SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY;
ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY
*
ERROR at line 1:
ORA-16416: No viable Physical Standby switchover targets available

Error from standby alert.log file

.... (PID:24072): No viable Physical Standby switchover targets available
ORA-16416 signalled during: ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY... 2020-02-27T19:36:42.425842-08:00
rfs (PID:36824): Database mount ID mismatch [0x5a5dee6f:0x5a5d7a7b] (1516105327:1516075643)
rfs (PID:36824): Not using real application clusters
2020-02-27T19:38:17.144104-08:00
.... (PID:24072): Using STANDBY_ARCHIVE_DEST parameter default value as /oraarch/ORCLP krsd.c:18141]
2020-02-27T19:38:17.154204-08:00
ALTER SYSTEM SET log_archive_dest_2='SERVICE=ORCLP AFFIRM SYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=ORCLP' SCOPE=BOTH;
2020-02-27T19:38:21.552799-08:00
ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY
2020-02-27T19:38:21.552940-08:00
TMI: adbdrv kcv_primary_switchover BEGIN 2020-02-27 19:38:21.552864
2020-02-27T19:38:21.553038-08:00
ALTER DATABASE COMMIT TO SWITCHOVER TO PHYSICAL STANDBY [Process Id: 24072] (ORCLP)
.... (PID:24072): Waiting for target standby to receive all redo
.... (PID:24072): Waiting for target standby to receive all redo
2020-02-27T19:38:21.553572-08:00
.... (PID:24072): Waiting for all non-current ORLs to be archived
2020-02-27T19:38:21.553661-08:00
.... (PID:24072): All non-current ORLs have been archived
2020-02-27T19:38:21.553741-08:00
.... (PID:24072): Waiting for all FAL entries to be archived
2020-02-27T19:38:21.553820-08:00
.... (PID:24072): All FAL entries have been archived
2020-02-27T19:38:21.553924-08:00
.... (PID:24072): Waiting for potential Physical Standby switchover target to become synchronized
2020-02-27T19:38:21.598598-08:00
Errors in file /home/oracle/diag/rdbms/ORCLP_stdby/ORCLP/trace/ORCLP_tt00_16934.trc:
ORA-16009: invalid redo transport destination
2020-02-27T19:38:21.598892-08:00
TT00 (PID:16934): krsg_check_connection: Error 16009 connecting to standby 'ORCLP'
2020-02-27T19:38:22.554301-08:00

Run below command to find out the Archive Destination status errors..

SQL> select DEST_ID, STATUS, DESTINATION from V$ARCHIVE_DEST_STATUS;
SQL> select DEST_ID,DEST_NAME,STATUS,TARGET,DESTINATION,ERROR,ALTERNATE from v$archive_dest

SQL> select GROUP#,THREAD#,BYTES/1024/1024/1024,ARCHIVED,STATUS from v$standby_log;

Also run below command to identify the gap

SQL> SELECT THREAD#, SEQUENCE# FROM V$THREAD;
SQL> SELECT THREAD#, LOW_SEQUENCE#, HIGH_SEQUENCE# FROM V$ARCHIVE_GAP;

After running the above commands analyzing the logs I see that the error due to invalid REDO LOG destination. I have created the directories as same as Primary on Standby site.

I also come across issue with LOG_ARCHIVE_DEST_2, after fixing the parameter it worked fine. Also, make sure LOG_ARCHIVE_DEST_STATE_2 enabled.

ORA-16474: target_db_name not found in the LOG_ARCHIVE_DEST_n parameter

I would strongly advise to use Data Guard Broker, it minimizes the errors, and switchover is very easy.

Refer below Data Guard presentation
Webinar: Data Guard Physical Standby Setup in Oracle?

Regards

Satishbabu Gunukula, Oracle ACE
http://oracleracexpert.com