[疑问]RMAN之snapshot control file

在rman中，有SNAPSHOT CONTROLFILE NAME这个参数，它是说明意思呢？

RMAN> SHOW SNAPSHOT CONTROLFILE NAME;

RMAN configuration parameters for database with db_unique_name HOU are:
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/product/11.1.0/db_1/dbs/snapcf_hou.f'; # default

可以看到，控制文件快照默认保存/u01/app/product/11.1.0/db_1/dbs/下

1.删除/u01/app/product/11.1.0/db_1/dbs/snapcf_hou.f，在rman中备份控制文件，控制文件快照在/u01/app/product/11.1.0/db_1/dbs/目录下自动产生。

2.只备份数据文件

<1>首先删除/u01/app/product/11.1.0/db_1/dbs/snapcf_hou.f

<2>关闭自动备份控制文件

CONFIGURE CONTROLFILE AUTOBACKUP OFF;

<3>然后备份数据文件7

RMAN> backup datafile 7;

Starting backup at 17-FEB-13
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00007 name=/u01/app/oradata/hou/anony_all_2010q4.dbf
channel ORA_DISK_1: starting piece 1 at 17-FEB-13
channel ORA_DISK_1: finished piece 1 at 17-FEB-13
piece handle=/var/rman_bk/copy_39o271ja_1_1.dbf tag=TAG20130217T145538 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 17-FEB-13

在/u01/app/product/11.1.0/db_1/dbs目录下依然生成snapcf_hou.f

网上很多人都说snapshot control file是在备份控制文件的时候产生的，但是我的实验测试显示不备份控制依然会产生snapshot control file。

到底snapshot control file是干什么用的呢？