Example of How To Resize the Online Redo Logfiles
EXAMPLE OF HOW TO RESIZE THE ONLINE REDO LOGS:
==============================================
Often times the online redo logs are sized too small causing database
performance problems.
The following is an example of how to resize the online log groups:
NOTE: Examples are given for 9i and higher. In prior releases, you needed
to use Server Manager and connect as the internal user.
1. First see the size of the current logs:
> sqlplus /nolog
SQL> connect / as sysdba
SQL> select group#, bytes, status from v$log;
GROUP# BYTES STATUS
---------- ---------- ----------------
1 1048576 INACTIVE
2 1048576 CURRENT
3 1048576 INACTIVE
Logs are 1MB from above, let's size them to 10MB.
2. Retrieve all the log member names for the groups:
SQL> select group#, member from v$logfile;
GROUP# MEMBER
--------------- ----------------------------------------
1 /usr/oracle/dbs/log1PROD.dbf
2 /usr/oracle/dbs/log2PROD.dbf
3 /usr/oracle/dbs/log3PROD.dbf
3. In older versions of the database you needed to shutdown and issue the following
commands in restricted mode. You can still do this, but the database can be online
to perform these changes.
Let's create 3 new log groups and name them groups 4, 5, and 6, each 10MB in
size:
SQL> alter database add logfile group 4
'/usr/oracle/dbs/log4PROD.dbf' size 10M;
SQL> alter database add logfile group 5
'/usr/oracle/dbs/log5PROD.dbf' size 10M;
SQL> alter database add logfile group 6
'/usr/oracle/dbs/log6PROD.dbf' size 10M;
4. Now run a query to view the v$log status:
SQL> select group#, status from v$log;
GROUP# STATUS
--------- ----------------
1 INACTIVE
2 CURRENT
3 INACTIVE
4 UNUSED
5 UNUSED
6 UNUSED
From the above we can see log group 2 is current, and this is one of the
smaller groups we must drop. Therefore let's switch out of this group into
one of the newly created log groups.
5. Switch until we are into log group 4, so we can drop log groups 1, 2, and 3:
SQL> alter system switch logfile;
** repeat as necessary until group 4 is CURRENT **
6. Run the query again to verify the current log group is group 4:
SQL> select group#, status from v$log;
GROUP# STATUS
--------- ----------------
1 INACTIVE
2 INACTIVE
3 INACTIVE
4 CURRENT
5 UNUSED
6 UNUSED
Note: redo log Group 1 or 2 or 3 can be active after "alter system switch log file" which means could not be dropped, in this case,
you need to do "alter system checkpoint" to make redo log groups 1,2 and 3 inactive.
7. Now drop redo log groups 1, 2, and 3:
SQL> alter database drop logfile group 1;
SQL> alter database drop logfile group 2;
SQL> alter database drop logfile group 3;
Verify the groups were dropped, and the new groups' sizes are correct.
SVRMGR> select group#, bytes, status from v$log;
GROUP# BYTES STATUS
--------- --------- ----------------
4 10485760 CURRENT
5 10485760 UNUSED
6 10485760 UNUSED
8. At this point, you consider taking a backup of the database.
9. You can now go out to the operating system and delete the files associated
with redo log groups 1, 2, and 3 in step 2 above as they are no longer
needed:
% rm /usr/oracle/dbs/log1PROD.dbf
% rm /usr/oracle/dbs/log2PROD.dbf
% rm /usr/oracle/dbs/log3PROD.dbf
Monitor the alert.log for the times of redo log switches. Due to increased
redo log size, the groups should not switch as frequently under the same
load conditions.
References:
===========
Chapter 6 of the Oracle8i Administrator's Guide, Release 8.1.5,
Part No. A67772-01 for further information on redo log maintenance.
Chapter 7 of the Oracle 9i Administrator's guide
Part No. A96521-01 for further information on redo log maintenance.
Chapter 6 of the Oracle 10g Administrator's guide
Part No. B10739-01 for further information on redo log maintenance.
Chapter 10 of the Oracle 11g Administrator's guide
Part No. B28310-04 for further information on redo log maintenance.
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