Accidental deletions are a common concern for administrators and developers alike. Fortunately, Oracle Database offers a powerful safety net known as the Flashback Drop Table feature, designed to mitigate the risk of unintended data loss. This feature allows you to recover dropped tables with ease, providing a safeguard against irreversible mistakes.
Understanding the Recycle Bin in Oracle Database
Central to the functionality of the Flashback Drop Table feature is the Recycle Bin, a hidden repository within the Oracle Database where dropped objects are retained temporarily. Think of it as a virtual recycling bin for your database, preserving dropped tables and their associated metadata until explicitly purged.
Enabling and Using the Recycle Bin
Enabling the Recycle Bin is a straightforward process, requiring only a simple alteration to your database settings:
ALTER SYSTEM SET RECYCLEBIN = ON;
Once enabled, any dropped tables will be automatically moved to the Recycle Bin instead of being permanently deleted. To retrieve a dropped table from the Recycle Bin, you can use the following SQL statement:
FLASHBACK TABLE table_name TO BEFORE DROP;
This command leverages the power of Oracle’s Flashback technology to restore the dropped table to its previous state, effectively rolling back the drop operation and salvaging your data from the brink of oblivion.
Prerequisites for Flashback Drop Table
It’s important to note that both the Flashback and Flash Recovery features must be enabled in your Oracle Database environment to utilise the Flashback Drop Table functionality effectively. Without these features enabled, the ability to recover dropped tables will be unavailable.
Executing a proof of concept
As a proof of concept, we will generate a table with 100 random numbers. After dropping the table, we will verify that it is in the recycle bin and proceed to recover it. Additionally, we will verify that all records are retrieved using a checksum.
SQL> CREATE TABLE test AS
SELECT TRUNC(DBMS_RANDOM.VALUE(0, 100)) AS random_number
FROM dual
CONNECT BY level <= 100;
Table created.
SQL> desc test
Name Null? Type
----------------------------------------- -------- ----------------------------
RANDOM_NUMBER NUMBER
SQL> select count(*), sum(random_number) from test;
COUNT(*) SUM(RANDOM_NUMBER)
---------- ------------------
100 4921
SQL> drop table test;
Table dropped.
SQL> SELECT ORIGINAL_NAME, TYPE, TS_NAME FROM RECYCLEBIN;
ORIGINAL_N TYPE TS_NAME
---------- ------------------------- ------------------------------
TEST TABLE USERS
SQL>
SQL> FLASHBACK TABLE test TO BEFORE DROP;
Flashback complete.
SQL> SELECT ORIGINAL_NAME, TYPE, TS_NAME FROM RECYCLEBIN;
no rows selected
SQL> select count(*), sum(random_number) from test;
COUNT(*) SUM(RANDOM_NUMBER)
---------- ------------------
100 4921
Using Drop with the Purge option
The DROP command can be used with the PURGE option as a finality clause, permanently removing objects from the database, bypassing the Recycle Bin entirely. When PURGE is specified, the dropped object is immediately and irreversibly eliminated from the database, freeing up space and resources. This option is particularly useful when there is certainty that the dropped object will not be needed again, and it ensures efficient management of database storage. It’s important to exercise caution when using the PURGE option, as it precludes any possibility of recovery, making it suitable only for situations where permanent deletion is intended.
In addition, the PURGE command can be used to remove an object from the recycle bin.
-- Check the objects in the recycle bin SELECT * FROM recyclebin; -- Purge all objects from the recycle bin PURGE RECYCLEBIN; -- Verify that the recycle bin is empty SELECT * FROM recyclebin;