Managing Redo Log Files

 Managing REDO Log Files:
    
     Redo log files record all changes made to data and provide a recovery mechanism from a system or media failure.

• Redo log files are organized into groups.
• An Oracle database requires at least two groups.
• Each redo log within a group is called a member.

How Redo Logs Work
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• Redo logs are used in a cyclic fashion.
• When a redo log file is full, LGWR will move to the next log group.
– This is called a log switch
– Checkpoint operation also occurs
– Information is written to the control file


How to add Redo log group:
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SQL> select *from v$log;

SQL> ALTER DATABASE ADD LOGFILE GROUP 3 '/u01/app/oracle/oradata/cts/log3a.rdo' SIZE 4M;


How to add a Redo log member into the redo log group:
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SQL>select *from v$logfile;

ALTER DATABASE ADD LOGFILE MEMBER
'/u01/app/oracle/oradata/cts/log1b.rdo' to group 1,   
'/u01/app/oracle/oradata/cts/log2b.rdo' to group 2,
'/u01/app/oracle/oradata/cts/log3b.rdo' to group 3;

How to drop a redo log group:
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SQL> ALTER DATABASE DROP LOGFILE GROUP 3;


How to drop a redo log group member:
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SQL> ALTER DATABASE DROP LOGFILE MEMBER '/u01/app/oracle/oradata/cts/log1b.rdo';


How to switche logfile and checkpoint force:

SQL> ALTER SYSTEM SWITCH LOGFILE;

SQL> ALTER SYSTEM CHECKPOINT;

       
Note :
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* We can't drop the CURRENT and ACTIVE redo log group as well as redo log member.
* We can't Resize the redolog group. If you want to increase the size of the redolog group then add new redolog group with new size and delete old redolog group.
* We can have different size for all redolog groups but have same size for all redolog groups.