重做日志

1. 数据字典视图v$log记录了当前数据库的日志组号，日志序列号和每个日志文件的大小(以字节为单位)，每个日志组的成员数量，以及日志组的当前状态
SYS@orcl>select group#,sequence#,bytes/1024/1024,members,archived,status from v$log;
GROUP#  SEQUENCE# BYTES/1024/1024 MEMBERS ARC STATUS
---------- ---------- --------------- ---------- --- ----------------
1   13        50            1 YES INACTIVE
2   14        50            1 NO  CURRENT
3   12        50            1 YES INACTIVE
2. 17:25:59 SYS@orcl>select * from v$logfile;
    GROUP# STATUS  TYPE    MEMBER  IS_
---------- ------- ------- ------------------------------ ---                status:stale:说明该文件内容是不完整的
  3   ONLINE  /u01/app/oracle/oradata/orcl/r NO                                空白：说明该日志组正在使用
    edo03.log                                                                invalid：表示该文件不能被访问
                                                                             deleted：表示该文件已经不再使用
  2   ONLINE  /u01/app/oracle/oradata/orcl/r NO
    edo02.log
  1   ONLINE  /u01/app/oracle/oradata/orcl/r NO
    edo01.log
3. 添加重做日志组
SYS@orcl>alter database add logfile group 4 ('/u01/app/oracle/oradata/orcl/redoa.log','/u01/app/oracle/oradata/orcl/redob.log') size 100M;
SYS@orcl>alter database add logfile group 5 ('/u01/app/oracle/oradata/orcl/redo11.log','/u01/app/oracle/oradata/orcl/redo22.log',
        '/u01/app/oracle/oradata/orcl/redo33.log') size 50M;
4. 验证日志组是否添加
SYS@orcl>col member for a30
SYS@orcl>select * from v$logfile;
GROUP# STATUS  TYPE    MEMBER  IS_
---------- ------- ------- ------------------------------ ---
3   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo03.log
2   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo02.log
1   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo01.log
4   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edoa.log
4   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edob.log
5   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo11.log
5   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo22.log
5   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo33.log
5. 删除日志组
SYS@orcl>alter database drop logfile group 5;
6. 验证日志组是否删除
SYS@orcl>select * from v$logfile;
    GROUP# STATUS  TYPE    MEMBER  IS_
---------- ------- ------- ------------------------------ ---
3   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo03.log
2   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo02.log
1   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edo01.log
4   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edoa.log
4   ONLINE  /u01/app/oracle/oradata/orcl/r NO
  edob.log
7. 向日志组中添加成员
SYS@orcl>alter database add logfile member '/u01/app/oracle/oradata/orcl/redo01a.log' to group 1,
                                           '/u01/app/oracle/oradata/orcl/redo02a.log' to group 2,
                                           '/u01/app/oracle/oradata/orcl/redo03a.log' to group 3;
8. 验证日志组成员数量
SYS@orcl>select GROUP#,SEQUENCE#,BYTES/1024/1024,MEMBERS,STATUS from v$log;
    GROUP#  SEQUENCE# BYTES/1024/1024 MEMBERS STATUS
---------- ---------- --------------- ---------- ----------------
     1   13       50             2     INACTIVE
     2   14       50             2     CURRENT
     3   12       50             2     INACTIVE
     4    0      100             2     UNUSED
9. 删除日志组成员
alter database drop logfile member '/u01/app/oracle/oradata/orcl/redo02a.log';
10.重做日志组更改大小的话，只能添加新的日志组，设置大小，然后删除之前的日志组。。。
11.清除联机重做日志
数据库处于归档模式时候，如果正在使用的重做日志文件损坏，重做日志不能完成归档，这个时候，要清除重做日志文件并且重新初始化重做日志文件
SYS@orcl>alter database claer logfile group 1;
12.强制切换日志组，强制触发检查点事件
18:31:01 SYS@orcl>alter system switch logfile;
System altered.
18:31:18 SYS@orcl>alter system checkpoint;
System altered.