Archived redo logfiles（归档重做日志）
因为在线重做日志的运行机制（循环使用的机制），会导致日志被覆盖，
为了保证日志不被覆盖，更长时间的保留，那么，在线重做日志切换之后，
将写满的在线重做日志，保存在另外一个存储位置，这种机制，称之为归档；
ARCn这个进程负责归档操作；
如果想要采用归档机制，那么必须将数据库置为归档模式；
如何查询当前数据库的归档模式？
SYS@orcl11g> archive log list;
Database log mode No Archive Mode -- 数据库日志模式（非归档）
Automatic archival Disabled -- 自动归档
Archive destination USE_DB_RECOVERY_FILE_DEST --归档存储位置
Oldest online log sequence 0 -- 最老的在线重做日志的序列号
Current log sequence 29 -- 当前日志序列号
SYS@orcl11g> select log_mode from v$database;
LOG_MODE
------------
NOARCHIVELOG
如何设置数据库为归档模式？
1.一致性关闭数据库
shutdown immediate；
2.将数据库启动到mount状态
startup mount；
3.修改数据库日志模式
SYS@orcl11g> alter database archivelog;
SYS@orcl11g> alter database noarchivelog; --归档模式，转换为非归档模式
4.打开数据库
alter database open；
5.查看日志模式：
SYS@orcl11g> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 0
Next log sequence to archive 29 -- 下一个要被归档的日志序列号
Current log sequence 29
归档模式的设置和管理；
设置归档的相关参数：
查看归档位置：
SYS@orcl11g> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST -- 默认的归档位置：闪回恢复区
Oldest online log sequence 0
Next log sequence to archive 29
Current log sequence 29
SYS@orcl11g> show parameter db_recovery_file_dest;
NAME TYPE VALUE
------------------------------------ ----------- ----------------------------------
db_recovery_file_dest string /u01/app/oracle/fast_recovery_area
db_recovery_file_dest_size big integer 4122M
可以手动修改归档位置：
SYS@orcl11g> show parameter log_archive_dest_
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_1 string (null)
log_archive_dest_10 string (null)
log_archive_dest_11 string (null)
log_archive_dest_12 string (null)
。。。。。
ORACLE11G版本，一共可以设置31个归档位置；
Oracle10g版本，一共可以设置10个归档位置
这么多的归档位置，主要是用于oracle的灾备软件：DATAGUARD
******************************
如何手动设置归档位置：
SYS@orcl11g> alter system set log_archive_dest_1='location=/u01/app/oracle/arch';
System altered.
SYS@orcl11g> host ls /u01/app/oracle/arch
SYS@orcl11g> alter system switch logfile;
System altered.
SYS@orcl11g> host ls /u01/app/oracle/arch
1_30_816622368.dbf
归档位置状态参数：
SYS@orcl11g> show parameter log_archive_dest_state_1;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_state_1 string enable
Values:
■ enable
Specifies that a valid log archive destination can be used for a subsequent
archiving operation (automatic or manual). This is the default.
■ defer
Specifies that valid destination information and attributes are preserved, but the
destination is excluded from archiving operations until re-enabled.
■ alternate
Specifies that a log archive destination is not enabled but will become enabled if
communications to another destination fail.
defer：
SYS@orcl11g> alter system set log_archive_dest_state_2=defer;
System altered.
SYS@orcl11g> alter system switch logfile;
System altered.
SYS@orcl11g> host ls /u01/app/oracle/arch*
/u01/app/oracle/arch:
1_30_816622368.dbf 1_31_816622368.dbf 1_32_816622368.dbf
/u01/app/oracle/arch2:
1_31_816622368.dbf
alternate：备胎
SYS@orcl11g> alter system set log_archive_dest_state_2=alternate;
System altered.
SYS@orcl11g> show parameter log_archive_dest_2;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2 string location=/u01/app/oracle/arch2
SYS@orcl11g> alter system set
log_archive_dest_1='location=/u01/app/oracle/arch mandatory noreopen alternate=log_archive_dest_2';
System altered.
[root@db253 mnt]# chown root.root /u01/app/oracle/arch
[root@db253 mnt]# ll -d /u01/app/oracle/arch
drwxr-xr-x 2 root root 4096 Jun 17 10:49 /u01/app/oracle/arch
SYS@orcl11g> alter system switch logfile;
System altered.
SYS@orcl11g> host ls /u01/app/oracle/arch*
/u01/app/oracle/arch:
1_30_816622368.dbf 1_32_816622368.dbf
1_31_816622368.dbf 1_33_816622368.dbf
/u01/app/oracle/arch2:
1_31_816622368.dbf 1_34_816622368.dbf
log_archive_dest_n:参数的配置
LOCATION=path_name -- location=/u01/app/oracle/arch
MANDATORY -- 强制的，表示这个归档位置，必须要归档成功
REOPEN[=seconds] -- 如果某个归档路径出现问题，那么，几秒钟重试
SYS@orcl11g> alter system set log_archive_dest_3='location=/u01/app/oracle/arch3 mandatory reopen=5';
System altered.
SYS@orcl11g> alter system switch logfile;
System altered.
SYS@orcl11g> host ls /u01/app/oracle/arch*
/u01/app/oracle/arch:
1_30_816622368.dbf 1_32_816622368.dbf
1_31_816622368.dbf 1_33_816622368.dbf
/u01/app/oracle/arch2:
1_31_816622368.dbf 1_35_816622368.dbf 1_37_816622368.dbf
1_34_816622368.dbf 1_36_816622368.dbf
/u01/app/oracle/arch3:
1_37_816622368.dbf
root#chown root.root /u01/app/oracle/arch3
SQL> alter system switch logfile;
SYS@orcl11g> host ls /u01/app/oracle/arch*
/u01/app/oracle/arch:
1_30_816622368.dbf 1_32_816622368.dbf
1_31_816622368.dbf 1_33_816622368.dbf
/u01/app/oracle/arch2:
1_31_816622368.dbf 1_35_816622368.dbf 1_37_816622368.dbf
1_34_816622368.dbf 1_36_816622368.dbf 1_38_816622368.dbf
/u01/app/oracle/arch3:
1_37_816622368.dbf
SYS@orcl11g> select group#,sequence#,status,archived from v$log;
GROUP# SEQUENCE# STATUS ARC
---------- ---------- ---------------- ---
1 39 CURRENT NO
2 38 ACTIVE NO
3 37 ACTIVE YES
多次切换之后，数据库hang住；
如果将数据库置为归档模式，但是，在线重做日志却没有被归档，那么，数据库hang住；
重新修改mandatory，reopen属性的归档位置，数据库继续正常运行；
表示归档成功位置的最小个数：
SYS@orcl11g> show parameter min_succeed
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_min_succeed_dest integer 1
归档进程设置参数：
SYS@orcl11g> show parameter log_archive_max_processes
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_max_processes integer 4
[oracle@db253 ~]$ ps -ef | grep ora_ | grep arc
oracle 23330 1 0 10:29 ? 00:00:00 ora_arc0_orcl11g
oracle 23362 1 0 10:29 ? 00:00:00 ora_arc1_orcl11g
oracle 23365 1 0 10:29 ? 00:00:00 ora_arc2_orcl11g
oracle 23368 1 0 10:29 ? 00:00:00 ora_arc3_orcl11g
SYS@orcl11g> show parameter log_archive_format
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_format string %t_%s_%r.dbf
归档相关的数据字典：
v$archived_log;
SYS@orcl11g> desc v$archived_log;
Name Null? Type
----------------------------------------- -------- ----------------------------
RECID NUMBER
STAMP NUMBER
NAME VARCHAR2(513)
DEST_ID NUMBER
THREAD# NUMBER
SEQUENCE# NUMBER
RESETLOGS_CHANGE# NUMBER
RESETLOGS_TIME DATE
RESETLOGS_ID NUMBER
FIRST_CHANGE# NUMBER
FIRST_TIME DATE
NEXT_CHANGE# NUMBER
NEXT_TIME DATE
BLOCKS NUMBER
BLOCK_SIZE NUMBER
CREATOR VARCHAR2(7)
REGISTRAR VARCHAR2(7)
STANDBY_DEST VARCHAR2(3)
ARCHIVED VARCHAR2(3)
APPLIED VARCHAR2(9)
DELETED VARCHAR2(3)
STATUS VARCHAR2(1)
COMPLETION_TIME DATE
DICTIONARY_BEGIN VARCHAR2(3)
DICTIONARY_END VARCHAR2(3)
END_OF_REDO VARCHAR2(3)
BACKUP_COUNT NUMBER
ARCHIVAL_THREAD# NUMBER
ACTIVATION# NUMBER
IS_RECOVERY_DEST_FILE VARCHAR2(3)
COMPRESSED VARCHAR2(3)
FAL VARCHAR2(3)
END_OF_REDO_TYPE VARCHAR2(10)
BACKED_BY_VSS VARCHAR2(3)
SYS@orcl11g> select sequence#,name from v$archived_log order by 1;
SEQUENCE# NAME
---------- --------------------------------------------------------------------------------
29 /u01/app/oracle/fast_recovery_area/ORCL11G/archivelog/2013_06_17/o1_mf_1_29_8vwxglwq_.arc
30 /u01/app/oracle/arch/1_30_816622368.dbf
