620.You are using the control file to maintain information about the database backups that are being
performed by Recovery Manager (RMAN).
Identify two scenarios is which you must have a recovery catalog. (Choose two.)
A. To store the backup information of multiple database
B. To restrict the amount of space that is used by the backups
C. To maintain a backup for a certain time is set by the CONTROL_FILE_RECORD_KEEP_TIME parameter.
D. To list the data files that were in a target database at a given time by using the AT option of REPORT SCHEMA command.
Answer: AD
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/backup.112/e10643/rcmsynta2006.htm#RCMRF90281
题中意在比较控制文件和恢复目录，指出两个必须只用恢复目录的场景：
A，可以存储多个数据库的备份信息，恢复目录可以做到，控制文件只能记录一个数据库的备份信息
D，atClause：
atClause
This subclause specifies a point in time as a time, SCN, or log sequence number. You must be connected to a recovery catalog when issuing a REPORT SCHEMAcommand with an AT clause.
| Syntax Element | Description |
|---|---|
AT SCN integer |
Specifies an SCN. |
AT SEQUENCE integer |
Specifies a log sequence number. The integer indicates the time when the specified log was first opened. |
THREAD integer |
Specifies a redo THREAD number. The integer indicates the time when the thread was first opened. |
AT TIME 'date_string' |
Specifies a date (see Example 3-14). The NLS_LANG and NLS_DATE_FORMAT environment
variables specify the format for the time. |
Example 3-14 Reporting a Database Schema
This example, which requires a recovery catalog, reports the names of all data files and tablespaces 20 minutes ago.