OCP-1Z0-053-V12.02-605题

605.What two are the prerequisites for enabling Flashback Database? (Choose two)

A. The database must be in ARCHIVELOG mode

B. The database must be in MOUNT EXCLUSIVE mode

C. The database must be opened in RESTRICTED mode

D. The database instance must be started in the NOMOUNT state

E. The database instance must have the keep buffer pool defined

Answer: AB

答案解析：

参考：闪回数据库：http://blog.csdn.net/rlhua/article/details/12421005

按以下步骤配置闪回数据库：

1.配置快速恢复区。

2.使用DB_FLASHBACK_RETENTION_TARGET初始化参数设置保留目标。可指定一个上限（以分钟为单位），指示数据库能够闪回到多长时间以前。 ALTER SYSTEM SETDB_FLASHBACK_RETENTION_TARGET=2880 SCOPE=BOTH 使用了2,880 分钟，相当于两天。此参数只是一个目标，并不提供任何保证。闪回时间间隔取决于快速恢复区中保存的闪回数据量。

3.使用以下命令启用闪回数据库：

ALTER DATABASE FLASHBACK ON;

必须先针对归档配置数据库，之后才能发出命令来启用闪回数据库。

可以使用以下查询来确定是否已启用闪回数据库：

SELECT flashback_on FROM v$database;

可使用ALTER DATABASE FLASHBACK OFF命令来禁用闪回数据库。这样，会自动删除所有现有的闪回数据库日志。

注：只有在独占模式下装载数据库后才能启用闪回数据库，在打开状态下则不可以。

参考：http://docs.oracle.com/cd/E11882_01/backup.112/e10642/flashdb.htm#BRADV593

Prerequisites for Flashback Database and Guaranteed Restore Points

To ensure successful operation of Flashback Database and guaranteed restore points, you must first set several key database options.

Flashback Database

Configure the following database settings before enabling Flashback Database:

• Your database must be running in ARCHIVELOG mode, because archived logs are used in the Flashback Database operation.

• You must have a fast recovery area enabled, because flashback logs can only be stored in the fast recovery area.

• For Oracle Real Application Clusters (Oracle RAC) databases, the fast recovery area must be in a clustered file system or in ASM.