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回收站(Recycle Bin）从原理上来说就是一个数据字典表，放置用户删除（drop）掉的数据库对象信息。用户进行删除操作的对象并没有被数据库删除，仍然会占用空间。除非是由于用户手工进行Purge或者因为存储空间不够而被数据库清掉。
如果一个表被drop删除，那么与表关联的对象、约束条件、索引都会一并删除。

2种查看回收站的当前状态：（默认是打开的）
SQL> show parameter bin
NAME TYPE VALUE

cursor_bind_capture_destination string memory+disk
recyclebin string on

SQL> SELECT Value FROM V$parameter WHERE Name = 'recyclebin';
VALUE

ON

启动或者关闭回收站里的每个会话（session）和系统（system），代码如下：

ALTER SYSTEM SET recyclebin = ON;
ALTER SESSION SET recyclebin = ON;
ALTER SYSTEM SET recyclebin = OFF;
ALTER SESSION SET recyclebin = OFF;

注：执行ALTER SESSION SET recyclebin = OFF只适用于当前会话窗口，重新复制新窗口默认回收站依旧是打开的，测试如下：
SQL> ALTER SESSION SET recyclebin = OFF;
Session altered.
新开窗口：
[oracle @strong ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Thu Jan 28 18:03:00 2018
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> show parameter bin
NAME TYPE VALUE

cursor_bind_capture_destination string memory+disk
recyclebin string on

修改system系统级别的测试如下：
SQL> ALTER SYSTEM SET recyclebin = OFF;
ALTER SYSTEM SET recyclebin = OFF
*
ERROR at line 1:
ORA-02096: specified initialization parameter is not modifiable with this
option
报错：不允许这样操作
原因：回收站是数据文件里面的动态参数，需要添加spoce=spfile，重启数据库才能修改成功


测试如下：
SQL> alter system set recyclebin=off scope=spfile;
System altered.

[root @strong ~]# reboot
Broadcast message from root @strong
(/dev/pts/5) at 18:05 ...
The system is going down for reboot NOW!


[root @strong ~]# su - oracle
[oracle @strong ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Thu Jan 18 18:10:29 2018
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options


SQL> show parameter bin

NAME TYPE VALUE

cursor_bind_capture_destination string memory+disk

recyclebin string OFF


注：生产线上建议把回收站设置为on打开，当我们有误操作删除表时，还可以到回收站找回（以上只是我本人的测试，不建议在生产线操作）。