rman中format参数(format_String clause)

我们经常在使用rman来备份数据库。在使用format指定备份集名称，经常会使用%U等参数，这些参数是什么意思呢？下面开始详细的介绍。

%c  The copy number of the backup piece within a set of duplexed
    backup pieces. If you did not duplex a backup, then this variable
    is 1 for backup sets and 0 for proxy copies.
    If one of these commands is enabled, then the variable shows the
    copy number. The maximum value for %c is 256. 
-->备份片的拷贝数，在一组备份片内。如果没有设置多备份集，那么这个参数默认设置为1并且0个拷贝片。如果设置了多备份集，这个变量显示的是拷贝数。%c的最大值时256.
-->这个参数很少用到。使用场景是需要将备份集保存到2个以及2个以上路径时使用。
-->如果将备份集保存到2个以上路径，需要rman做如下设置
-->CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;
-->CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 2;
-->在format '路径1','路径2'

%d The name of the database.
-->数据库名称

%D The current day of the month (in format DD)
-->日期

%F Combination of DBID, day, month, year, and sequence into a unique
and repeatable generated name.
-->复合format == c-IIIIIIIIII-YYYYMMDD-QQ，其中IIIIIIIIII为dbid，YYYYMMDD为年月日，QQ为十六进制的备份片的多个copy的序号（00-ff）

%M The month (format MM)
-->月份

%n The name of the database, padded on the right with x characters
to a total length of eight characters. (AKA: Porn star alias name)
For example, if the scott is the database name, %n= scottxxx.
-->数据库的8位长度的db_name，不足部分用“x”后面填充

%p The piece number within the backup set. This value starts at 1
for each backup set and is incremented by 1 as each backup piece
is created. Note: If you specify PROXY, then the %p variable must
be included in the FORMAT string either explicitly or implicitly within %U.
-->备份片序号

%s The backup set number. This number is a counter in the control file that
is incremented for each backup set. The counter value starts at 1 and is
unique for the lifetime of the control file. If you restore a backup
control file, then duplicate values can result.
Also, CREATE CONTROLFILE initializes the counter back to 1.
-->备份集序号

%t The backup set time stamp, which is a 4-byte value derived as the
number of seconds elapsed since a fixed reference time.
The combination of %s and %t can be used to form a unique name for
the backup set.
-->备份集的timestamp

%T The year, month, and day (YYYYMMDD)
-->时间格式

%u An 8-character name constituted by compressed representations of
the backup set number and the time the backup set was created.
-->8位的唯一序列号

%U A convenient shorthand for %u_%p_%c that guarantees uniqueness in
generated backup filenames.
If you do not specify a format, RMAN uses %U by default.
-->复合format %u_%p_%c

%Y The year (YYYY)
-->年

%% Specifies the '%' character. e.g. %%Y translates to %Y.
-->这个很少使用