目的:修改当前在线日志从默认50M增加至512M。

1.查看当前日志组的状态
SQL> select group#,members,bytes/1024/1024,status from v$log;

    GROUP#    MEMBERS BYTES/1024/1024 STATUS
---------- ---------- --------------- ----------------
         1          1              50 INACTIVE
         2          1              50 CURRENT
         3          1              50 INACTIVE

2.查看在线日志组的位置
SQL> select MEMBER from v$logfile;

MEMBER
--------------------------------------------------------------------------------
/u01/app/oradata/ARPDB/redo01.log
/u01/app/oradata/ARPDB/redo02.log
/u01/app/oradata/ARPDB/redo03.log

3.新增group 4-6日志组，大小为512M
alter database add logfile group 4 ('/u01/app/oradata/ARPDB/redo04.log') size 512M;
alter database add logfile group 5 ('/u01/app/oradata/ARPDB/redo05.log') size 512M;
alter database add logfile group 6 ('/u01/app/oradata/ARPDB/redo06.log') size 512M;

4.切换当前日志到新的日志组
alter system switch logfile;   
alter system switch logfile;

---让在线日志组，变成inactive的方式，执行如下命令：
alter system checkpoint;

5.删除旧的日志组
alter database drop logfile group 1;
alter database drop logfile group 2;
alter database drop logfile group 3;

6.查看修改后的日志组的状态信息：
SQL> select group#,members,bytes/1024/1024,status from v$log;

    GROUP#    MEMBERS BYTES/1024/1024 STATUS
---------- ---------- --------------- ----------------
         4          1             512 INACTIVE
         5          1             512 CURRENT
         6          1             512 UNUSED