OCP-1Z0-053-V12.02-374题

 

374.Which of the following statements are true regarding the Recycle Bin? (Choose all that apply.)

A. The Recycle Bin is a physical storage area for dropped objects.

B. The Recycle Bin is a logical container for dropped objects.

C. The Recycle Bin stores the results of a Flashback Drop operation.

D. The objects in the Recycle Bin are stored in the tablespace in which they were created.

Answer: BD

答案解析：

参考：http://blog.csdn.net/rlhua/article/details/12407737

如果不启用回收站，则删除表时，与该表及其从属对象关联的空间会立即变为可回收（也就是说，该空间可用于其它对象）。

 

如果启用了回收站，则删除表时，与该表及其从属对象关联的空间不会立即变为可回收，即使该空间确实显示在DBA_FREE_SPACE中。

 

相反，会在回收站中引用删除的对象，这些对象仍属于其各自的所有者。在空间不紧张时，绝不会把回收站对象使用的空间自动回收。

这样，你就能在尽可能长的期限内恢复回收站对象。

 

将删除的表“移动”到回收站时，将使用系统生成的名称对该表及其关联对象和约束条件进行重命名。重命名惯例如下：BIN$unique_id$version。

 

其中，unique_id是该对象的全局唯一标识符，包含26 个字符，用于在所有数据库之间唯一地标识回收站名称，而version是数据库分配的版本号。

 

回收站本身是一个数据字典表，用于维护已删除对象的原始名称与各自系统生成名称之间的关系。可使用DBA_RECYCLEBIN视图查询回收站。

The recycle bin is actually a data dictionary table containing information about dropped objects. Dropped tables and any associated objects such as indexes, constraints, nested tables, and the likes are not removed and still occupy space. They continue to count against user space quotas, until specifically purged from the recycle bin or the unlikely situation where they must be purged by the database because of tablespace space constraints.

Each user can be thought of as having his own recycle bin, because, unless a user has the SYSDBA privilege, the only objects that the user has access to in the recycle bin are those that the user owns. A user can view his objects in the recycle bin using the following statement:

SELECT * FROM RECYCLEBIN;

When you drop a tablespace including its contents, the objects in the tablespace are not placed in the recycle bin and the database purges any entries in the recycle bin for objects located in the tablespace. The database also purges any recycle bin entries for objects in a tablespace when you drop the tablespace, not including contents, and the tablespace is otherwise empty.

官网参考：http://docs.oracle.com/cd/E11882_01/server.112/e25494/tables.htm#sthref2315