1、查询数据库中的重做日志组
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 64 52428800 512 1 NO CURRENT 1522229 17-MAY-19 2.8147E+14
2 1 62 52428800 512 1 NO INACTIVE 1502072 16-MAY-19 1515210 17-MAY-19
3 1 63 52428800 512 1 NO INACTIVE 1515210 17-MAY-19 1522229 17-MAY-19
2、具体查看日志文件详情（位置）
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_RECOVERY_DEST_FILE
---------- ------- ------- -------------------------------------------------- ------------------------------
3 ONLINE /u01/app/oraData/orcl/redo03.log NO
2 ONLINE /u01/app/oraData/orcl/redo02.log NO
1 ONLINE /u01/app/oraData/orcl/redo01.log NO
3、创建重做日志组
SQL> alter database add logfile ('/u01/app/oraData/orcl/hbk01.rdo','/u01/app/oraData/orcl/hbk02.rdo') size 5M;
Database altered.
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_RECOVERY_DEST_FILE
---------- ------- ------- -------------------------------------------------- ------------------------------
3 ONLINE /u01/app/oraData/orcl/redo03.log NO
2 ONLINE /u01/app/oraData/orcl/redo02.log NO
1 ONLINE /u01/app/oraData/orcl/redo01.log NO
4 ONLINE /u01/app/oraData/orcl/hbk01.rdo NO
4 ONLINE /u01/app/oraData/orcl/hbk02.rdo NO
可以看到多了两个重做日志文件hbk01.rdo,hbk02.rdo，组的编号为4,查询v$log可以知道4号组的status为UNUSED，表示新建状态，未使用。
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 64 52428800 512 1 NO CURRENT 1522229 17-MAY-19 2.8147E+14
2 1 62 52428800 512 1 NO INACTIVE 1502072 16-MAY-19 1515210 17-MAY-19
3 1 63 52428800 512 1 NO INACTIVE 1515210 17-MAY-19 1522229 17-MAY-19
4 1 0 5242880 512 2 YES UNUSED 0 0
可以看出我们创建重做日志组的编号默认系统产生
我们也可以知道组编号
SQL> alter database add logfile group 8 ('/u01/app/oraData/orcl/hbk10.rdo') size 5M;
Database altered.
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_RECOVERY_DEST_FILE
---------- ------- ------- -------------------------------------------------- ------------------------------
3 ONLINE /u01/app/oraData/orcl/redo03.log NO
2 ONLINE /u01/app/oraData/orcl/redo02.log NO
1 ONLINE /u01/app/oraData/orcl/redo01.log NO
4 ONLINE /u01/app/oraData/orcl/hbk01.rdo NO
4 ONLINE /u01/app/oraData/orcl/hbk02.rdo NO
8 ONLINE /u01/app/oraData/orcl/hbk10.rdo NO
6 rows selected.
以上方式都是新创建重做日志组，并添加重做日志文件（成员），有的时候我们需要在原来的组上添加日志文件（成员），可以使用如下 to group语法，有一个知识点：同一个重做日志组中的日志文件（成员）大小都必须相同，所以在原有重做日志组中添加日志成员，不用指定大小。
SQL> alter database add logfile member '/u01/app/oraData/orcl/hbk8.rdo' to group 8;
Database altered.
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_RECOVERY_DEST_FILE
---------- ------- ------- -------------------------------------------------- ------------------------------
3 ONLINE /u01/app/oraData/orcl/redo03.log NO
2 ONLINE /u01/app/oraData/orcl/redo02.log NO
1 ONLINE /u01/app/oraData/orcl/redo01.log NO
4 ONLINE /u01/app/oraData/orcl/hbk01.rdo NO
4 ONLINE /u01/app/oraData/orcl/hbk02.rdo NO
8 ONLINE /u01/app/oraData/orcl/hbk10.rdo NO
8 INVALID ONLINE /u01/app/oraData/orcl/hbk8.rdo NO
7 rows selected.
在原来存在的日志组中添加日志成员，将显示INVALID ONLINE（不可访问）
4、删除重做日志组
删除重做日志组只是更新了控制文件，被删除的组所拥有的重做日志文件并没有从操作系统中删除，需要手工删除，而且只能删除状态是INAVTIVE的重做日志组，如果想删除当前（CURRENT）的重做日志组，必须手工切换，可以使用alter system switch logfile,而且每个数据库至少需要有两组重做日志组，因为要循环使用。
删除之前先查询下
SQL> select group#,status from v$log;
GROUP# STATUS
---------- ----------------
1 CURRENT
2 INACTIVE
3 INACTIVE
4 UNUSED
8 UNUSED
像组2和组3都可以删，而组1为当前使用，不能删，除非切换使用日志组。删除之前先记下文件位置，方便手动执行操作系统rm删除命令
alter database drop logfile group 2;
5、删除日志成员
需要注意的是，一个日志组中至少需要保留一个成员，而且只能删除状态不是ONLINE或CURRENT的日志成员。
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_RECOVERY_DEST_FILE
---------- ------- ------- -------------------------------------------------- ------------------------------
3 ONLINE /u01/app/oraData/orcl/redo03.log NO
2 ONLINE /u01/app/oraData/orcl/redo02.log NO
1 ONLINE /u01/app/oraData/orcl/redo01.log NO
4 ONLINE /u01/app/oraData/orcl/hbk01.rdo NO
4 ONLINE /u01/app/oraData/orcl/hbk02.rdo NO
8 ONLINE /u01/app/oraData/orcl/hbk10.rdo NO
8 INVALID ONLINE /u01/app/oraData/orcl/hbk8.rdo NO
2 INVALID ONLINE /u01/app/oraData/orcl/redo02_new.log NO
1 INVALID ONLINE /u01/app/oraData/orcl/redo01_new.log NO
9 rows selected.
SQL> alter database drop logfile member '/u01/app/oraData/orcl/hbk10.rdo';
alter database drop logfile member '/u01/app/oraData/orcl/hbk10.rdo'
*
ERROR at line 1:
ORA-00362: member is required to form a valid logfile in group 8
ORA-01517: log member: '/u01/app/oraData/orcl/hbk10.rdo'
SQL> alter database drop logfile member '/u01/app/oraData/orcl/hbk8.rdo';
Database altered.
6、日志组切换状态
如果重做日志组的状态是CURRENT,则执行alter system switch logfile将变成其他状态。
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 64 52428800 512 2 NO CURRENT 1522229 17-MAY-19 2.8147E+14
2 1 62 52428800 512 2 NO INACTIVE 1502072 16-MAY-19 1515210 17-MAY-19
3 1 63 52428800 512 1 NO INACTIVE 1515210 17-MAY-19 1522229 17-MAY-19
4 1 0 5242880 512 2 YES UNUSED 0 0
8 1 0 5242880 512 1 YES UNUSED 0 0
SQL> alter system switch logfile;
System altered.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 64 52428800 512 2 NO ACTIVE 1522229 17-MAY-19 1528474 17-MAY-19
2 1 62 52428800 512 2 NO INACTIVE 1502072 16-MAY-19 1515210 17-MAY-19
3 1 63 52428800 512 1 NO INACTIVE 1515210 17-MAY-19 1522229 17-MAY-19
4 1 65 5242880 512 2 NO CURRENT 1528474 17-MAY-19 2.8147E+14
8 1 0 5242880 512 1 YES UNUSED 0 0
一开始是组1为CURRENT，切换后，组4为CURRENT，可以多次执行这个命令，只有一个组会变成CURRENT，关于哪个组会变成下一个CURRENT,我也不知道，应该有算法吧。
如果重做日志组的状态是ACTIVE，执行如下命令，会把状态变成INACTIVE
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 64 52428800 512 2 NO INACTIVE 1522229 17-MAY-19 1528474 17-MAY-19
2 1 62 52428800 512 2 NO INACTIVE 1502072 16-MAY-19 1515210 17-MAY-19
3 1 63 52428800 512 1 NO INACTIVE 1515210 17-MAY-19 1522229 17-MAY-19
4 1 65 5242880 512 2 NO ACTIVE 1528474 17-MAY-19 1528568 17-MAY-19
8 1 66 5242880 512 1 NO CURRENT 1528568 17-MAY-19 2.8147E+14
SQL> alter system checkpoint;
System altered.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 64 52428800 512 2 NO INACTIVE 1522229 17-MAY-19 1528474 17-MAY-19
2 1 62 52428800 512 2 NO INACTIVE 1502072 16-MAY-19 1515210 17-MAY-19
3 1 63 52428800 512 1 NO INACTIVE 1515210 17-MAY-19 1522229 17-MAY-19
4 1 65 5242880 512 2 NO INACTIVE 1528474 17-MAY-19 1528568 17-MAY-19
8 1 66 5242880 512 1 NO CURRENT 1528568 17-MAY-19 2.8147E+14
当前组4是ACTIVE状态，执行命令后变成INACTIVE状态了。
7、查看重做日志是否归档
SQL> select group#,status,archived from v$log;
GROUP# STATUS ARC
---------- ---------------- ---
1 INACTIVE NO
2 INACTIVE NO
3 INACTIVE NO
4 INACTIVE NO
8 CURRENT NO
NO表示未归档，YES表示已归档。
因为我的没有开启归档模式，所以都显示NO
SQL> select name,log_mode from v$database;
NAME LOG_MODE
--------- ------------
ORCL NOARCHIVELOG