oracle First In First Out (FIFO)/Last In First Out (LIFO) .....

You discover that your Recycle Bin contains two tables with the same name, MY_TABLE. You also have a table named MY_TABLE in your schema. You execute the following statement:

FLASHBACK TABLE my_table TO BEFORE DROP RENAME TO my_table2;

What will be the result of executing this statement?

A. One of the tables is recovered from the Recycle Bin using a First In First Out (FIFO) approach.

B. One of the tables is recovered from the Recycle Bin using a Last In First Out (LIFO) approach.

C. Both the tables are recovered from the Recycle Bin with one table renamed to MY_TABLE2 and the other to a system-generated name.

D. None of the tables are recovered from the Recycle Bin, and the statement returns an error.

Answer: B

SQL> create table aa1 as select dict_code,dict_desc from base_dict;

表已创建。

已用时间: 00: 00: 00.06
SQL> desc aa1;
名称是否为空? 类型
-----------------------------------------------------------------------------------------------

DICT_CODE VARCHAR2(50)

DICT_DESC                                                         VARCHAR2(400)

SQL> create table aa as select * from tab;

表已创建。

已用时间: 00: 00: 00.14
SQL> drop table aa; ---->该删除的是tab模拟表

表已删除。

已用时间: 00: 00: 00.07
SQL> rename aa1 to aa;

表已重命名。

已用时间: 00: 00: 00.04
SQL> drop table aa; --->该表是基于base_dict创建的表

表已删除。

已用时间: 00: 00: 00.01
SQL> sho recycle;
ORIGINAL NAME    RECYCLEBIN NAME                OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
AA               BIN$LdL8XIZ2T9q/VKY/co2S8A==$0 TABLE        2013-04-19:11:40:09
AA               BIN$LVSXxo8OTfyfxTFN+sw8Bg==$0 TABLE        2013-04-19:11:39:55
SQL> FLASHBACK TABLE aa to before drop rename to aa1;

闪回完成。

已用时间: 00: 00: 00.01

SQL> desc aa1; --------->返回的结果证明：recyclebin表2个相同的表闪回机制：后进先出
名称是否为空? 类型
-----------------------------------------------------------------------------------------------
DICT_CODE VARCHAR2(50)
DICT_DESC            VARCHAR2(400)

SQL>当空间压力出现时，Oracle会覆盖些回收站对象从而自动回收表空间。Oracle根据先进先出的原则来选择丢弃对象进行删除，所以最先被丢弃的对象也最先被清除。而对象的清除仅仅是为了解决产生的空间压力问题，所以会尽可能清除少的对象来满足空间压力的要求。这样处理，既最大限度地保证了对象在回收站中的可用时间，又减少了Oracle在事物处理时的性能影响。

ITPub博客

OCP(11g)-----> oracle First In First Out (FIFO)/Last In First Out

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