I was recently recovering a backup of a standby database, the standby was from a primary that was a RAC with 2 nodes. I had the following error:
SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-38856: cannot mark instance UNNAMED_INSTANCE_2 (redo thread 2) as enabled
Solution
Edit the .ora file add the following:
*._no_recovery_through_resetlogs=TRUE
Save
SQL> shutdown immediate;
ORA-01109: database not open
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 6313463808 bytes
Fixed Size 2264976 bytes
Variable Size 1677721712 bytes
Database Buffers 4613734400 bytes
Redo Buffers 19742720 bytes
Database mounted.
SQL> alter database open resetlogs;
Database altered.
shutdown and remove the line added above and restart instance