💡 After restoring an RAC database to a standalone database through RMAN, we tried to drop the redolog groups belongs to thread 2. We hit the below error.

SQL> alter database drop logfile group 3;
alter database drop logfile group 3
*
ERROR at line 1:
ORA-00350: log 4 of instance DBATST2 (thread 2) needs to be archived
ORA-00312: online log 3 thread 2: '/u01/oracle/DBATST/onlinelog/redo03.log'

SQL> startup
ORACLE instance started.
Total System Global Area 1787138048 bytes
Fixed Size                  2254104 bytes
Variable Size             956304104 bytes
Database Buffers          822083584 bytes
Redo Buffers                6496256 bytes
Database mounted.
ORA-03113: end-of-file on communication channel
Process ID: 32429
Session ID: 1137 Serial number: 5

Check log

[oracle@ora2 ~]$ tail -f /u01/oracle/diag/rdbms/orcl/orcl/trace/alert_orcl.log
......
Errors in file /u01/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_32429.trc:
ORA-16038: log 3 sequence# 510 cannot be archived
ORA-19502: write error on file "", block number  (block size=)
ORA-00312: online log 3 thread 1: '/u01/oracle/oradata/orcl/redo03.log'
USER (ospid: 32429): terminating the instance due to error 16038

more /u01/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_32429.trc
......
Executing ASYNC actions
----- END DDE Actions Dump (total 0 csec) -----
ORA-16038: log 3 sequence# 510 cannot be archived
ORA-19502: write error on file "", block number  (block size=)
ORA-00312: online log 3 thread 1: '/u01/oracle/oradata/orcl/redo03.log'
kjzduptcctx: Notifying DIAG for crash event

SOLUTION:

Before dropping, we need to clear the redolog using below command.

SQL> conn / as sysdba
Connected to an idle instance.
SQL> startup mount
ORACLE instance started.
Total System Global Area 1787138048 bytes
Fixed Size                  2254104 bytes
Variable Size             956304104 bytes
Database Buffers          822083584 bytes
Redo Buffers                6496256 bytes
Database mounted.
SQL> alter database clear unarchived logfile group 3;
Database altered.
SQL> alter database open;
Database altered.
SQL>

Now try to drop again:

rm -rf /u01/oracle/DBATST/onlinelog/redo03.log
SQL> alter system switch logfile;
SQL> alter database drop logfile group 8;
Database altered.