Four characteristics of database transactions: ensuring the integrity and consistency of data operations
In the information age, database systems play a vital role. They carry massive amounts of data and provide data storage and management services for various application systems. In order to ensure the atomicity, consistency, isolation and persistence of database operations, the database introduces the concept of transactions. A transaction is a logical unit of database operations. It combines multiple database operations and executes them as a whole. Either all operations are completed successfully or no operations are performed at all.

1. Four characteristics of transactions
1.1 Atomicity

Atomicity means that all operations in a transaction are either successfully executed or all failed and rolled back. The database system processes transactions as a whole and does not allow transactions to be partially completed. For example, in a transfer operation, either the funds are successfully transferred from account A to account B, or no transfer operation is performed. There will be no situation where the deduction of account A is successful but account B does not receive the funds.

1.2 Consistency

Consistency means that after the transaction is completed, the database must be in a consistent state, that is, it meets all database constraints and business rules. For example, in a bank deposit operation, after the deposit is successful, the account balance must increase the deposit amount, otherwise it violates the consistency constraint of the database.

1.3 Isolation

Isolation means that multiple concurrent transactions do not affect each other, and the execution of each transaction is as if it is carried out in a separate database. The database system implements transaction isolation through a concurrency control mechanism. Common transaction isolation levels include:

Read Uncommitted: A transaction can read uncommitted data.

Read Committed: A transaction can only read committed data.

Repeatable Read: During the execution of a transaction, the data seen is consistent with the data seen at the beginning of the execution.

Serializable: No two transactions can be executed at the same time, just like a transaction is executed sequentially.

1.4 Durability

Persistence means that once a transaction is successfully committed, its changes to the database will be permanently saved and will not be lost even if the database system fails. The database system ensures the persistence of transactions through logging and fault recovery mechanisms.

2. Implementation of transactions
The database system implements the four major characteristics of transactions through the following mechanisms:

Log records: The database system records the operations of all transactions so that transactions can be rolled back or the database state can be restored in the event of a failure.

Concurrency control: The database system uses lock mechanisms or other concurrency control mechanisms to ensure that multiple concurrent transactions do not affect each other.

Fault recovery: The database system has a fault recovery mechanism that can restore the database state after a failure.

3. Application scenarios of transactions
Transactions are widely used in various scenarios where data integrity and consistency need to be guaranteed, such as:

Bank transfer: Ensure the atomicity of the transfer operation, either the transfer is successful or no transfer operation is performed.

Airline ticket booking: Ensure that only one passenger can book the same ticket seat at the same time.

Online shopping: Ensure the consistency of the shopping process, such as the user’s order, payment, and delivery operations are successfully completed.
4. Summary
Database transactions are an important concept in database systems. They provide strong protection for data by ensuring the atomicity, consistency, isolation, and persistence of data operations. Understanding the four characteristics and application scenarios of transactions can help you better design and develop database applications and ensure data security and integrity.

Here are some additional suggestions:

Choose the appropriate isolation level based on the application scenario.
Try to minimize the scope of transactions to improve concurrency performance.
Use optimistic locking mechanisms to improve concurrency performance.
Perform regular database backup and recovery drills.