dataguard-ora-00261 Errors and Solutions

Error | resolution
In the Dataguard environment if we are doing failover, we may encounter ORA-00261 errors, the following is the cause of the error and the solution.
If you need to switch because of a network problem, the RFS process on the standby side usually does not realize that primary is inaccessible, so the RFS process does not release the current standby redo log file.
If the primary end of the database instance is interrupted by a failure, the RFS process in the standby side will normally immediately realize that primary is inaccessible and immediately release the current standby redo log file.
As long as the RFS process does not release the STANDBY redo log file, the Execute ALTER DATABASE RECOVER MANAGED STANDBY Database Finish command will find the following error message in the Alertlog file
Warning:log 4 of Thread 1 is being archived or modified
Recovery interrupted.
Media Recovery failed with error 261
If you execute the switch when you report the above error, the following error occurs:
Ora-16139:media Recovery Required

Therefore, you must check the Alertlog file until you find the following information to indicate that the RFS process has released the standby redo log file, which can be done at this time:
Rfs:possible Network disconnect with primary database

There are two ways to drive the RFS process to release standby redo log files:
1. Waiting for the RFS process to network timeout usually takes about 8 minutes
2. Close the standby database and then turn it back on, forcing the RFS process to release standby redo log
We can monitor when the RFS process is released through the V$managed_standby view

Implement failover:
ALTER database RECOVER MANAGED STANDBY database FINISH;
The following information is displayed in Alertlog to indicate that finish was successful:
Terminal Incomplete Recovery:until Change 3738452
Terminal Incomplete Recovery:end-of-redo Log allocation
Terminal incomplete recovery:log 4 reserved for thread 1 seq# 8772
TERMINAL RECOVERY changing datafile format version from 8.0.0.0.0 to 9.0.0.0.0
Switching logfile format version from 8.0.0.0.0 to 9.0.0.0.0
Terminal Incomplete recovery:clearing standby redo logs.
Terminal incomplete Recovery:thread 1 seq# 8772 Redo required
Terminal Incomplete Recovery:end-of-redo Log/global/oradata/ctsdb/stdby_redo04.log
Identified End-of-redo for thread 1 sequence 8772
Terminal incomplete Recovery:end checkpoint SCN 3738453
Media Recovery Complete
Switching logfile format version from 9.0.0.0.0 to 8.0.0.0.0
Terminal Incomplete recovery:successful Completion
Begin:wait for standby logfiles to be archived
Wed Sep 1 13:42:28 2004
Arc1:evaluating Archive Log 4 thread 1 sequence 8772
Wed Sep 1 13:42:28 2004
Arc0:evaluating Archive Log 4 thread 1 sequence 8772
Wed Sep 1 13:42:28 2004
Arc1:beginning to archive log 4 thread 1 sequence 8772
Wed Sep 1 13:42:28 2004
Arc0:unable to archive log 4 thread 1 sequence 8772
Wed Sep 1 13:42:28 2004
Creating archive Destination log_archive_dest_1: '/global/oradata/ctsdb/archive/arch1_8772.log '
Wed Sep 1 13:42:28 2004
Log actively being archived by another process
Wed Sep 1 13:42:28 2004
arc1:completed Archiving log 4 thread 1 sequence 8772
Wed Sep 1 13:42:43 2004
End:all standby logfiles have been archived
Resetting standby activation ID 4038461969 (0XF0B60A11)
Completed:alter database RECOVER MANAGED STANDBY database FINISH

Finsh succeeds and then executes the switch:
ALTER DATABASE COMMIT to switchover to PRIMARY;

After the switch succeeds, restart the database:
SHUTDOWN IMMEDIATE;
STARTUP;