Manual Recovery - control files, redo log,etc

Recovering from Loss of a Control File

Losing one of the multiplexed control files immediately aborts the instance.
If you have not lost every control file, recovering from this failure is fairly straightforward.

SQL> startup nomount
SQL> select name, value from v$spparameter2 where name = 'control_files';

In the next step, you change the value of CONTROL_FILES in the SPFILE and restart theinstance, as you can see here:
SQL> alter system
set control_files ='/u02/oradata/ord/control01.ctl',
'/u06/oradata/ord/control02.ctl'4 scope = spfile;
SQL> shutdown immediate
SQL> startup

Recovering from Loss of a Redo Log File

A database instance stays up as long as at least one member of a redo log group is available. The alert log records the loss of a redo log group member.

1. Verify which redo log file group member is missing.
2. Archive the log file group’s contents; if you clear this log file group before archiving it, youmust back up the full database to ensure maximum recoverability of the database in the caseof the loss of a datafile. Use the command ALTER SYSTEM ARCHIVE LOG GROUP groupnum; toforce the archive operation.
3. Clear the log group to re-create the missing redo log file members using the command ALTER DATABASE CLEAR LOGFILE GROUP groupnum; you can also replace the missing member by copying one of the good group members to the location of the missing member

SQL> select * from v$logfile order by group#;
SQL> alter system archive log group 1;
SQL> alter database clear logfile group 1;
SQL> select * from v$logfile order by group#;