CONFIGURE BACKUP OPTIMIZATION
------------------------------------什么是backup optimization?
oracle通过optimization来有选择backup datafile，archivelog，backup set，跳过那些已存在的满足条件的。
条件都哪些呢？
----datafile
The datafile must have the same DBID, checkpoint SCN, creation SCN, and RESETLOGS SCN and time as a datafile already in a backup. The datafile must be offline-normal, read-only, or closed normally.
--前提是数据文件必须处于offline-normal，read-only，closed normally才激活optimization，才会进一步验证。数据文件要具有一样的DBID,checkpoin SCN，creation SCN，resetlogs SCN，time as a datafile already in a backup（个人理解是已存在的备份的创建时间）。
----archivelog
Same DBID, thread, sequence number, and RESETLOGS SCN and time.
--相同的DBID，线程，序列号和resetlogs SCN/time
----backupset
Same DBID, backup set record ID and stamp
-相同 DBID，backup set，记录ID和时间戳
----------------------------------------怎么启用optimization
----查看opitimization的状态
RMAN> SHOW BACKUP OPTIMIZATION;
----默认是off
----------启用
RMAN> CONFIGURE BACKUP OPTIMIZATION ON;
----------关闭
RMAN> CONFIGURE BACKUP OPTIMIZATION OFF;
RMAN在下列条件下才激活optimization
1.configure backup optimization on;
2.运行一下命令时参考bakcup database
backup archivelog with all or like options
backup recovery area
backup recovery files
backup datafilecopy
3.同时只能有一个通道被分配SBT/DISK,同一个bakcup命令中不能包含SBT和DISK.
------------------------------------retention policise，redundancy和optimization的优先级
例：read-only tablespace users retention policese 7 days，bakcuped 31-1；
optimization on
在28-2的时候，执行backup会再备份users，因为时间超过了retention的7天，这时retention的优先级大于optimization；
待续。。。以下8-27新增
关于optimization和redundancy的关系
1.10g以后redundancy参数设置的值即为保留的备份数，redundancy 2 即保留2份，不同于9i；
2.增量备份的时候，level0级开始到下一个level0之间的备份当作一份。
比如redundancy为1. 周一备份的level0，周2level1，周3level1.在周三的时候执行delete obsolete并不会删除level0。
because this backup is not redundant: the Tuesday level 1 backup could be used to recover the Monday level 0 backup to a time between noon on Tuesday and noon on Wednesday.
因为周1到周3的3个备份才是一个完整的用来recovery的备份。
如果在周四的时候执行level0备份，然后delete obsolete才会删除周1的level0以及周2，周三的level1.