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;

表已建立。

已用時間: 00: 00: 00.06
SQL> desc aa1;
名稱是否為空? 型別
-----------------------------------------------------------------------------------------------

DICT_CODE VARCHAR2(50)

DICT_DESC                                                         VARCHAR2(400)

SQL> create table aa as select * from tab;

表已建立。

已用時間: 00: 00: 00.14
SQL> drop table aa; ----&gt該刪除的是tab模擬表

表已刪除。

已用時間: 00: 00: 00.07
SQL> rename aa1 to aa;

表已重新命名。

已用時間: 00: 00: 00.04
SQL> drop table aa; ---&gt該表是基於base_dict建立的表

表已刪除。

已用時間: 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;

閃回完成。

已用時間: 00: 00: 00.01

SQL> desc aa1; ---------&gt返回的結果證明：recyclebin表2個相同的表閃回機制：後進先出
名稱是否為空? 型別
-----------------------------------------------------------------------------------------------
DICT_CODE VARCHAR2(50)
DICT_DESC            VARCHAR2(400)

SQL>當空間壓力出現時，Oracle會覆蓋些回收站物件從而自動回收表空間。Oracle根據先進先出的原則來選擇丟棄物件進行刪除，所以最先被丟棄的物件也最先被清除。而物件的清除僅僅是為了解決產生的空間壓力問題，所以會盡可能清除少的物件來滿足空間壓力的要求。這樣處理，既最大限度地保證了物件在回收站中的可用時間，又減少了Oracle在事物處理時的效能影響。

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

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