How To Resize the Online Redo Logfiles in Oracle Database

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:

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. 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.

How To Resize the Online Redo Logfiles in Oracle Database

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