How to delete data space in oracle

As the amount of enterprise data continues to grow, data management has become a key issue that organizations and enterprises must face and solve. One of them is how to delete data and reclaim space. Oracle, as a common relational database management system, provides some powerful features and tools in terms of data deletion and space reclamation, which will be introduced in detail below.

1. The concept of deleting data space in Oracle

Deleting data space in Oracle refers to deleting the space occupied by tables, indexes, constraints and other objects that are no longer needed. It is generally divided into There are two ways of physical deletion and logical deletion.

Physical deletion is to directly delete the data from the disk physically and cannot be restored, while logical deletion marks the data as "deleted" and is not directly cleared from the disk. At this time, it can be restored through operation to recover data.

In Oracle, logical deletion can be achieved using delete statements, for example:

DELETE FROM table_name WHERE criteria;

And physical deletion requires the use of TRUNCATE TABLE statement, as follows:

TRUNCATE TABLE table_name;

It should be noted that , TRUNCATE TABLE is different from DELETE FROM in that it will recycle the table's data for reuse instead of clearing it directly. Therefore, in some cases, TRUNCATE TABLE is a more efficient method.

2. Oracle’s principles for deleting data space

When deleting data space, we need to follow the following principles:

1. Commit transaction

Before deleting data, the transaction of the current session needs to be committed to ensure that changes to the data take effect and will not be rolled back.

2. Disable constraints

When deleting a table, you need to consider whether there are any constraints such as foreign keys, because if there are such constraints, you must first disable them, otherwise the deletion will fail. . The statement to disable constraints is as follows:

ALTER TABLE table_name DISABLE CONSTRAINT constraint_name;

3. Backup data

Before performing the deletion operation, it is best to perform a data backup to avoid data loss.

4. Delete in batches

If you want to delete a large amount of data, it is best to delete it in batches to avoid performance problems caused by deleting a large amount of data at once.

3. How to delete data space in Oracle

In addition to using DELETE FROM and TRUNCATE TABLE statements, Oracle also provides some other powerful features and tools to delete data space. Below we will Introduced one by one:

1. Flashback Drop

Flashback Drop is a concept introduced in Oracle 10g, which allows us to undo the delete operation while retaining the data file. We can use the following statement to enable Flashback Drop:

ALTER SYSTEM SET recyclebin=on;

With Flashback Drop, once we perform a DELETE or TRUNCATE operation and the data is moved to the recycle bin, we can use the following statement to restore it:

FLASHBACK TABLE table_name TO BEFORE DROP;

2. Purge

Purge is a tool used to clear the recycle bin objects. We can use the following statement to clear the recycle bin:

PURGE RECYCLEBIN;

If you need to delete a specific Object, you can use the following statement:

PURGE TABLE table_name;

3. Table partition

Oracle table partitioning is to divide the table into multiple parts according to the specified strategy, and each part is managed independently Data can be cleared independently. Table partitioning can improve database performance and reliability. When deleting, data can be controlled based on partitions.

4. Automatically delete partition tables recursively

When we want to delete a partition table, we must delete each partition one by one, which is very tedious. Therefore, Oracle introduced automatic recursive deletion of partitioned tables. When creating a partitioned table, you can specify the ON DELETE CASCADE option, as follows:

CREATE TABLE test_table (  
    id INT,
    created_at DATE,
    data VARCHAR2(5000)
)
PARTITION BY RANGE (created_at)
INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))
(
    PARTITION p_initial VALUES LESS THAN (TO_DATE('01-01-2022','DD-MM-YYYY'))
);

When we execute the following statement, all partitions will be automatically deleted:

DELETE FROM test_table WHERE created_at < TO_DATE('01-01-2021', 'DD-MM-YYYY');

4. Conclusion

Oracle deletion of data space is crucial for enterprise data management, and plays a great role in reducing system bottlenecks and improving system performance. Through the introduction of this article, readers can become familiar with the principles and methods of deletion space in Oracle database, which provides a reference for practical operations. It should be noted that before deleting a data space, you must be cautious, back up, and understand the consequences of the operation.

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