查看重做日志的信息,用数据字典v$log:
SQL> set line 120
SQL> select * from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          5          1   52428800 CURRENT          NO
         2          3          1   52428800 INACTIVE         NO
         3          4          1   52428800 INACTIVE         NO

可知该数据库中有三个重做日志组,每组有一个重做日志文件,它们的序列号分别是345(必须连续的),且都是非归档的,大小都一样。
对status的解释:
inactive:表示实例已恢复,不再需要这组联机重做日志组了
current:当前组,隐含该联机重做日志
active:表示这组联机重做日志组是活动的但不是当前组,在实例恢复时需要这组联机重做日志组
unused:表示oracle服务器从未写过该组联机重做日志组,刚刚被添加进去的


查看每个重做日志组中成员的信息,用数据字典v$logfile:
SQL> select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                                                  IS_
---------- ------- ------- ------------------------------------------------------- ---
         3 STALE   ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO03.LOG        NO
         2 STALE   ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO02.LOG        NO
         1         ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01.LOG        NO

可知每组重做日志组中的成员都在同一个目录下,且都是联机重做日志文件。
status解释:
空白:正在使用
stale:该文件的内容不完全
invalid:该文件不可以被访问
deleted:该文件不再有用


开始工作前先备份!(详见备份)
添加一组重做日志组:
SQL>alter database add logfile
2   ('c:\disk3\orcl\onlinelog\redo 04A.log',
3    'c:\disk6\orcl\onlinelog\redo 04B.log',
4    'c:\disk9\orcl\onlinelog\redo 04C.log')
5   size 15M;
数据库已更改。

SQL> select group#,sequence#,members,bytes,status,archived from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          5          1   52428800 CURRENT          NO
         2          3          1   52428800 INACTIVE         NO
         3          4          1   52428800 INACTIVE         NO
         4          0          3   15728640 UNUSED           YES


SQL> col member for a45
SQL> select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         3 STALE   ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO03. NO
                           LOG

         2 STALE   ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO02. NO
                           LOG

         1         ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01. NO
                           LOG

         4         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 04A.LOG          NO
         4         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 04B.LOG          NO

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         4         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 04C.LOG          NO

已选择6行。


SQL> alter database drop logfile group 3;

数据库已更改。

SQL> select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         2 STALE   ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO02. NO
                           LOG

         1         ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01. NO
                           LOG

         4         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 04A.LOG          NO
         4         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 04B.LOG          NO
         4         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 04C.LOG          NO

 

SQL> alter database add logfile
  2  ('c:\disk3\orcl\onlinelog\redo 03A.log',
  3  'c:\disk6\orcl\onlinelog\redo 03B.log',
  4  'c:\disk9\orcl\onlinelog\redo 03C.log')
  5  size 15M;

数据库已更改。

SQL> alter database drop logfile group 2;

数据库已更改。

SQL> select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         3         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 03A.LOG          NO
         1         ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01. NO
                           LOG

         4         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 04A.LOG          NO
         4         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 04B.LOG          NO
         4         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 04C.LOG          NO
         3         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 03B.LOG          NO
         3         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 03C.LOG          NO

已选择7行。

SQL> alter database add logfile
  2  ('c:\disk3\orcl\onlinelog\redo 02A.log',
  3  'c:\disk6\orcl\onlinelog\redo 02B.log',
  4  'c:\disk9\orcl\onlinelog\redo 02C.log')
  5  size 15M;

数据库已更改。

SQL> select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         3         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 03A.LOG          NO
         2         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 02A.LOG          NO
         1         ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01. NO
                           LOG

         4         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 04A.LOG          NO
         4         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 04B.LOG          NO
         4         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 04C.LOG          NO
         3         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 03B.LOG          NO
         3         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 03C.LOG          NO
         2         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 02B.LOG          NO

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         2         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 02C.LOG          NO

已选择10行。

SQL> alter system switch logfile;

系统已更改。

 

SQL> select group#,sequence#,members,bytes,status,archived from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          5          1   52428800 ACTIVE           NO
         2          6          3   15728640 CURRENT          NO
         3          0          3   15728640 UNUSED           YES
         4          0          3   15728640 UNUSED           YES

SQL> alter system switch logfile;

系统已更改。

SQL> select group#,sequence#,members,bytes,status,archived from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          5          1   52428800 ACTIVE           NO
         2          6          3   15728640 ACTIVE           NO
         3          7          3   15728640 CURRENT          NO
         4          0          3   15728640 UNUSED           YES

SQL> alter system switch logfile;

系统已更改。

SQL> select group#,sequence#,members,bytes,status,archived from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          5          1   52428800 ACTIVE           NO
         2          6          3   15728640 ACTIVE           NO
         3          7          3   15728640 ACTIVE           NO
         4          8          3   15728640 CURRENT          NO

SQL> alter system switch logfile;

系统已更改。

SQL> select group#,sequence#,members,bytes,status,archived from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          9          1   52428800 CURRENT          NO
         2          6          3   15728640 ACTIVE           NO
         3          7          3   15728640 ACTIVE           NO
         4          8          3   15728640 ACTIVE           NO

SQL> alter system switch logfile;

系统已更改。

SQL> select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         3         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 03A.LOG          NO
         2         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 02A.LOG          NO
         1         ONLINE  C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01. NO
                           LOG

         4         ONLINE  C:\DISK3\ORCL\ONLINELOG\REDO 04A.LOG          NO
         4         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 04B.LOG          NO
         4         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 04C.LOG          NO
         3         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 03B.LOG          NO
         3         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 03C.LOG          NO
         2         ONLINE  C:\DISK6\ORCL\ONLINELOG\REDO 02B.LOG          NO

    GROUP# STATUS  TYPE    MEMBER                                        IS_
---------- ------- ------- --------------------------------------------- ---
         2         ONLINE  C:\DISK9\ORCL\ONLINELOG\REDO 02C.LOG          NO

已选择10行。

SQL> select group#,sequence#,members,bytes,status,archived from v$log;

    GROUP#  SEQUENCE#    MEMBERS      BYTES STATUS           ARC
---------- ---------- ---------- ---------- ---------------- ---
         1          9          1   52428800 ACTIVE           NO
         2         10          3   15728640 CURRENT          NO
         3          7          3   15728640 ACTIVE           NO
         4          8          3   15728640 ACTIVE           NO

SQL>

切换来切换去,第一组重做日志组不是活动组就是当前组,暂定问题7
碰到重做日志组序列号不连续,定为问题8
到此,基本上重做日志就已完成。最后一步就是把原有的旧文件删除。