29 November, 2012

Recycle Bin in Database


Oracle introduced in database 10g new feature called "Recycle Bin" to store the dropped database objects.
If any table is dropped then any associated object to this table such as indexes, constraints and any other dependent object are renamed with a prefix of bin$$.

Use of Recycle Bin
If user drop an important object accidentally, and he want to get it again.
With Recycle Bin feature user can easily restore the dropped objects.

Enable and Disable Recycle Bin
You can use the below query to distinguish which Recycle Bin is enabled or no

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

It will return on or off
on means that Recycle Bin is enabled and off is disabled.

You can enable and disable Recycle Bin per session and system, there fore you can use the below scripts to enable and disable Recycle Bin per session or system.

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



Get Contents of Recycle Bin
To get the dropped object in Recycle Bin, you can use any one of the below query statements.

 SELECT * FROM RECYCLEBIN;  
   
 SELECT * FROM USER_RECYCLEBIN;  
   
 SELECT * FROM DBA_RECYCLEBIN;  

Restore Dropped Objects
You can use the below syntax to restore dropped objects

 FLASHBACK TABLE <<Dropped_Table_Name>> TO BEFORE DROP RENAME TO <<New_Table_Name>>;  

Note that RENAME TO portion in restore statement is optional and you should use it if you want to restore dropped object with new name.

Clearing the Recycle Bin
You can clear specific entries in Recycle Bin or complete Recycle Bin

a- Clear Specific Table
PURGE TABLE <<Table_NAME>>;

b- Clear specific index
PURGE INDEX <<Index_NAME>>;

c- Clear every objects associated with specific table space
PURGE TABLESPACE<<Table_NAME>>;

d- Clear objects of a specific user in table space
PURGE TABLESPACE<<Table_NAME>> USER <<User_Name>>;

e- Clear complete Recycle Bin
PURGE TABLE <<Table_NAME>>;

e- Clear Complete Recycle Bin
PURGE RECYCLEBIN;

f- You can clear the table from RECYCLE Bin while dropping it
DROP TABLE <<Table_Name>> PURGE;

Demo
Now I will take a demo and for clarifying  Recycle Bin feature

1-Enable Recycle Bin feature

ALTER SYSTEM SET recyclebin = ON;  

2- Create DEMO_RECYCLEBIN database table

 CREATE TABLE DEMO_RECYCLEBIN (COL1 NUMBER);  

3- Insert one record in DEMO_RECYCLEBIN table

 INSERT INTO DEMO_RECYCLEBIN (COL1)  
    VALUES (1);  
   
 COMMIT;  

4- Drop  DEMO_RECYCLEBIN  table

 DROP TABLE DEMO_RECYCLEBIN;  

5- Query the Recycle Bin contents

SELECT * FROM USER_RECYCLEBIN;  

The data will be like below

6- Restore DEMO_RECYCLEBIN table from Recycle Bin

 FLASHBACK TABLE DEMO_RECYCLEBIN TO BEFORE DROP;  

7- Quert DEMO_REYCLEBIN after restoring

 SELECT * FROM DEMO_RECYCLEBIN;  

It will return the data existed before dropping

8- Drop table again and clear the Recycle Bin

 DROP TABLE DEMO_RECYCLEBIN PURGE;  


Thanks
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