[oracle@ora10g ~]$ cd $ORACLE_BASE/flash_recovery_area/ORA10G/archivelog
[oracle@ora10g archivelog]$ ll
total 8
drwxr-x--- 2 oracle oinstall 4096 Sep 24 11:46 2014_09_24
[oracle@ora10g archivelog]$ mv 2014_09_24/* .
[oracle@ora10g archivelog]$ ll
total 6636
drwxr-x--- 2 oracle oinstall 4096 Sep 24 11:59 2014_09_24
-rw-r----- 1 oracle oinstall 597504 Sep 24 11:46 o1_mf_1_10_b24ho39f_.arc
-rw-r----- 1 oracle oinstall 5473792 Sep 24 11:35 o1_mf_1_3_b24gz52r_.arc
-rw-r----- 1 oracle oinstall 373248 Sep 24 11:35 o1_mf_1_4_b24gz81d_.arc
-rw-r----- 1 oracle oinstall 180224 Sep 24 11:35 o1_mf_1_5_b24gzbb6_.arc
-rw-r----- 1 oracle oinstall 33792 Sep 24 11:35 o1_mf_1_6_b24gzd6y_.arc
-rw-r----- 1 oracle oinstall 26624 Sep 24 11:35 o1_mf_1_7_b24gzky8_.arc
-rw-r----- 1 oracle oinstall 1536 Sep 24 11:35 o1_mf_1_8_b24gzqnt_.arc
-rw-r----- 1 oracle oinstall 57344 Sep 24 11:44 o1_mf_1_9_b24hjflc_.arc
这里共有8个归档日志文件被“删除”
2. 进入RMAN，对归档日志进行交叉校验
[oracle@ora10g archivelog]$ exit
exit
host command complete
RMAN> crosscheck archivelog all;
released channel: ORA_DISK_1
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=145 devtype=DISK
validation failed for
archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_3_b24gz52r_.arc recid=208 stamp=859116904
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_4_b24gz81d_.arc recid=209 stamp=859116904
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_5_b24gzbb6_.arc recid=210 stamp=859116906
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_6_b24gzd6y_.arc recid=211 stamp=859116908
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_7_b24gzky8_.arc recid=212 stamp=859116914
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_8_b24gzqnt_.arc recid=213 stamp=859116919
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_9_b24hjflc_.arc recid=214 stamp=859117453
validation failed for archived log
archive log filename=/u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2014_09_24/o1_mf_1_10_b24ho39f_.arc recid=215 stamp=859117603
Crosschecked 8 objects
-rw-r----- 1 oracle oinstall 606K Sep 24 12:00 ora10g-4175411955_20140924_859118422_297.arc
-rw-r----- 1 oracle oinstall 166M Sep 24 12:02 ora10g-4175411955_20140924_859118425_298.db
-rw-r----- 1 oracle oinstall 610K Sep 24 12:02 ora10g-4175411955_20140924_859118562_299.arc
-rw-r----- 1 oracle oinstall 7.3M Sep 24 12:02 ora10g-c-4175411955-20140924-01.ctl
可以看到，备份全部完成了，共生成了2个归档日志备份集（arc），1个数据库备份集(db)以及控制文件备份集（ctl），这里有个细节要注意，由于我在脚本中写入了%s参数，从上面生成备份集生成的时间以及顺序可以发现RMAN备份这样一个顺序：
1. 对现有可以备份的数据库归档日志文件做一个备份
2. 对数据库进行备份
3. 切换一下日志，对完成全库备份后的归档日志再做一个备份（即使你没有通过RMAN> sql "alter system archive log current";来手动切）
4. 对控制文件备份（包括spfile，生成在同一个备份集）
我们可以看一下详细的日志输出，来对这个顺序有更深刻的了解：
Starting backup at 24-914
current log archived
using channel ORA_DISK_1
channel ORA_DISK_1: starting compressed archive log backupset
channel ORA_DISK_1: specifying archive log(s) in backup set
input archive log thread=1 sequence=11 recid=216 stamp=859118422
channel ORA_DISK_1: starting piece 1 at 24-914
channel ORA_DISK_1: finished piece 1 at 24-914
piece handle=/u01/orabackup/backupsets/ora10g-4175411955_20140924_859118422_297.arc tag=ARC_BAK
comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:03
Finished backup at 24-914
Starting backup at 24-914
using channel ORA_DISK_1
channel ORA_DISK_1: starting compressed full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/u01/app/oracle/oradata/ora10g/system01.dbf
input datafile fno=00003 name=/u01/app/oracle/oradata/ora10g/sysaux01.dbf
input datafile fno=00002 name=/u01/app/oracle/oradata/ora10g/undotbs01.dbf
input datafile fno=00005 name=/u01/app/oracle/oradata/ora10g/example01.dbf
input datafile fno=00006 name=/u01/app/oracle/oradata/ora10g/zlm01.dbf
input datafile fno=00004 name=/u01/app/oracle/oradata/ora10g/users01.dbf
channel ORA_DISK_1: starting piece 1 at 24-914
channel ORA_DISK_1: finished piece 1 at 24-914
piece handle=/u01/orabackup/backupsets/ora10g-4175411955_20140924_859118425_298.db tag=DB_BAK
comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:02:16
Finished backup at 24-914
Starting backup at 24-914
current log archived
using channel ORA_DISK_1
channel ORA_DISK_1: starting compressed archive log backupset
channel ORA_DISK_1: specifying archive log(s) in backup set
input archive log thread=1 sequence=12 recid=217 stamp=859118561
channel ORA_DISK_1: starting piece 1 at 24-914
channel ORA_DISK_1: finished piece 1 at 24-914
piece handle=/u01/orabackup/backupsets/ora10g-4175411955_20140924_859118562_299.arc tag=ARC_BAK
comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:02
Finished backup at 24-914
Starting Control File and SPFILE Autobackup at 24-914
piece handle=/u01/orabackup/backupsets/ora10g-c-4175411955-20140924-01.ctl comment=NONE
Finished Control File and SPFILE Autobackup at 24-914
顺序执行的4个部分，分别生成了4个备份集，虽然从日志来看，并没有发现备份完数据库以后，RMAN对归档日志进行了切换，但实际上确实是如此的，因为此刻我并没有对数据库进行切换归档操作。其实在RMAN对数据库备份之后对日志切换后再把归档日志备份一遍，是为了能让尽可能多的数据库改动都被写入磁盘，方便将来用备份集恢复。
对数据库的DML操作是通过写入online redo logfile来保证其一致性的，即使是undo中的数据，也会写入redo日志，我们称之为undo的redo，undo的redo向量与redo的redo向量合并为一条redo记录，被写入online redo logfile，而归档日志的作用，就是当online redo logfile要被刷新时，先对这些要刷新的内容进行归档，那么既然redo内容包含了所以的数据库的更改，恢复时也必须要使用归档日志来进行recover，把数据库推进到一致性状态。
RMAN是属于非一致性的备份，可以在数据库open状态下对数据库进行备份，要使不一致性备份的数据库达到一致性状态，那么就只有靠归档日志来实现了。那么，当RMAN切换日志的那一刻，可以保证数据库的最新更改内容被写到这个归档日志中，并对其备份，那么备份时间点之前的那些归档，就不再需要了。
考虑到备份全部归档会浪费大量磁盘空间，也没有这个必要，我们可以在RMAN备份前，先删除一部分归档，使归档备份集可以小一点，在磁盘空间比较紧张的情况下尤为需要注意，删除归档，可以使用以下的命令：
--删除7天前归档
RMAN> delete noprompt archivelog all completed before ‘sysdate-7‘;
或
RMAN> delete noprompt archivelog until time ‘sysdate-7‘;
--删除7小时前归档
RMAN> delete noprompt archivelog all completed
before ‘sysdate-7/24‘;
或
RMAN> delete noprompt archivelog until time ‘sysdate-7/24‘;
注意语法区别，前者有all关键字，而后者没有，不能互换使用，否则会报错：
RMAN> delete noprompt archivelog all until time ‘sysdate-7‘;
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-00558: error encountered while parsing input commands
RMAN-01009: syntax error: found "until": expecting one of: "backed, completed, device, like, ;, tag"
RMAN-01007: at line 1 column 32 file: standard input
RMAN> delete noprompt archivelog completed before ‘sysdate-7/24‘;
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-00558: error encountered while parsing input commands
RMAN-01009: syntax error: found "completed": expecting one of: "all, double-quoted-string, from, high, integer, like, logseq, low, scn, sequence, single-quoted-string, time, until"
RMAN-01007: at line 1 column 28 file: standard input
删除完以后，记得crosscheck一下，再把失效的归档日志记录从控制文件中去掉
RMAN> crosscheck achivelog all;
RMAN> delete noprompt expired archivelog all;
备份的时候还可以再利用压缩特性（RMAN> backup as compressed backupset ...），使备份集更加小，但可能带来的副作用是备份和恢复时间会适当久一些，看磁盘空间和时间哪个更重要了。这样，我们的备份集才是最精简的。
