MAINTAINING REDO LOG FILES

REDO LOGFILES

Redo log files provide the means to redo transaction in the event of a database failure

Online redo log file groups

• A set of identical copies of online redo log file is called an online redo log file group
• The LGWR background process concurrently writes the same information to all online redo log files in a group
• The oracle server needs a minimus of two online redo log file groups for the normal operation of a database

Online redo log file member

• each online redo log file in a group is called a member
• each member in a group has identical log sequence number and of the same size
• the corrent log sequence number is stored in the control file and in the header of all datafiles

Log switch

When the current online redo logfile group filled LGWR begins writing to the next group

this is called a log switch

this command is showing the redolog groups

SQL>select * from v$log;

this command is showing the redolog files

SQL>select * from v$logfile;

adding online redo log file group

SQL>alter database add logfile group3('/oracle/satish/9i/oradata/redo3a.log','/oracle/satish/9i/oradata/redo3b.log') size 5m;

adding online redo logfile member

SQL>alter database add logfile member '/oracle/satish/9i/oradata/redo3c.log' to group 3;

Relocation or renaming online redo log files

tow wayes is there

1)alter database

SQL>alter database rename file 'path1' to 'path2'

2)add new member and drop old member

Drop online redo log file groups

SQL>alter database drop logfile group 3;

• An instance require atleast two groups of online redo log files
• An active or current froup can not be dropped

Droping online redo log file members

SQL>alter database drop logfile member '/oracle/satish/9i/oradata/redo3a.log';

• we can not drop the last member
• we can not drop the current member
• if the databse is running in archive mode and the log file group to which the member belong is not archived then the member can not be dropped

Resize the redo log file

we can not resize the redo log file

just we can create another file and delete oldfile.

Forcing log switch

SQL>alter system switch logfile;

--satish