Resizing / Recreating Online Redo Log Files

One of the best ways I have found to resize or recreate online redo log files and keep the current sequence is to perform it online. In this example, we will resize all online redo logs from 100MB to 250MB while the database is running and use SQL*Plus to drop/recreate them in stages.

Before looking at the tasks involved to perform the resize, let's look at the current online redo log groups and their sizes:

SQL> SELECT a.group#, a.member, b.bytes
 2  FROM v$logfile a, v$log b WHERE a.group# = b.group#;

   GROUP# MEMBER                                          BYTES
---------- ---------------------------------------- ------------
        1 /u03/app/oradata/ORA920/redo_g01a.log     104,857,600
        1 /u04/app/oradata/ORA920/redo_g01b.log     104,857,600
        1 /u05/app/oradata/ORA920/redo_g01c.log     104,857,600
        2 /u03/app/oradata/ORA920/redo_g02a.log     104,857,600
        2 /u04/app/oradata/ORA920/redo_g02b.log     104,857,600
        2 /u05/app/oradata/ORA920/redo_g02c.log     104,857,600
        3 /u03/app/oradata/ORA920/redo_g03a.log     104,857,600
        3 /u04/app/oradata/ORA920/redo_g03b.log     104,857,600
        3 /u05/app/oradata/ORA920/redo_g03c.log     104,857,600

9 rows selected.

Now let's take a look at the steps involved to resize / recreate all online redo log groups:

---

1. Make the last redo log CURRENT

   Force a log switch until the last redo log is marked "CURRENT" by issuing the following command:

   SQL> select group#, status from v$log;
   
      GROUP# STATUS
   ---------- ----------------
           1 CURRENT
           2 INACTIVE
           3 INACTIVE
   
   SQL> alter system switch logfile;
   
   SQL> alter system switch logfile;
   
   SQL> select group#, status from v$log;
   
      GROUP# STATUS
   ---------- ----------------
           1 INACTIVE
           2 INACTIVE
           3 CURRENT
   

2. Drop first redo log

   After making the last online redo log file the CURRENT one, drop the first online redo log:

   SQL> alter database drop logfile group 1;
   
   Database altered.

3. Re-create dropped online redo log group

   Re-create the dropped redo log group with different size (if desired):

   SQL> alter database add logfile group 1 (
    2  '/u03/app/oradata/ORA920/redo_g01a.log', 
    3  '/u04/app/oradata/ORA920/redo_g01b.log',
    4  '/u05/app/oradata/ORA920/redo_g01c.log') size 250m reuse;
   
   Database altered.

4. Force another log switch

   After re-creating the online redo log group, force a log switch. The online redo log group just created should become the "CURRENT" one:

   SQL> select group#, status from v$log;
   
      GROUP# STATUS
   ---------- ----------------
           1 UNUSED
           2 INACTIVE
           3 CURRENT
   
   SQL> alter system switch logfile;
   
   SQL> select group#, status from v$log;
   
      GROUP# STATUS
   ---------- ----------------
           1 CURRENT
           2 INACTIVE
           3 ACTIVE

5. Loop back to Step 2 until all logs are rebuilt

   After re-creating an online redo log group, continue to re-create (or resize) all online redo log groups until all of them are rebuilt.

---

After rebuilding (resizing) all online redo log groups, here is a snapshot of all physical files:

SQL> SELECT a.group#, a.member, b.bytes
 2  FROM v$logfile a, v$log b WHERE a.group# = b.group#;

   GROUP# MEMBER                                          BYTES
---------- ---------------------------------------- ------------
        1 /u03/app/oradata/ORA920/redo_g01a.log     262,144,000
        1 /u04/app/oradata/ORA920/redo_g01b.log     262,144,000
        1 /u05/app/oradata/ORA920/redo_g01c.log     262,144,000
        2 /u03/app/oradata/ORA920/redo_g02a.log     262,144,000
        2 /u04/app/oradata/ORA920/redo_g02b.log     262,144,000
        2 /u05/app/oradata/ORA920/redo_g02c.log     262,144,000
        3 /u03/app/oradata/ORA920/redo_g03a.log     262,144,000
        3 /u04/app/oradata/ORA920/redo_g03b.log     262,144,000
        3 /u05/app/oradata/ORA920/redo_g03c.log     262,144,000

9 rows selected.