Understand the ACID properties and transaction management of MySQL and PostgreSQL

Understand the ACID properties and transaction management of MySQL and PostgreSQL

ACID (Atomicity, Consistency, Isolation, and Durability) properties and transaction management are very important concepts when developing database applications. This article will introduce MySQL and PostgreSQL, two popular relational database systems, and focus on their characteristics in terms of ACID properties and transaction management.

MySQL is an open source relational database management system that is widely used in the development of small and medium-sized applications and websites. PostgreSQL is also an open source relational database management system that is considered a powerful and scalable option, especially suitable for large enterprise-level applications.

1. Atomicity
   The atomicity in the ACID attribute means that a transaction (transaction) either all executes successfully or all fails and is rolled back. In MySQL, you can use the three statements BEGIN, COMMIT and ROLLBACK to control the start, commit and rollback of a transaction. The following is an example of MySQL atomicity:

BEGIN;
INSERT INTO users VALUES (1, 'John');
INSERT INTO transactions VALUES (100, 'John', ' Payment', 50);
COMMIT;

In PostgreSQL, the atomicity of transactions is achieved through BEGIN, COMMIT and ROLLBACK statements, similar to MySQL. The following is an example of PostgreSQL atomicity:

BEGIN;
INSERT INTO users VALUES (1, 'John');
INSERT INTO transactions VALUES (100, 'John', 'Payment', 50);
COMMIT;

2. Consistency (Consistency)
   Consistency in the ACID attribute means that the state of the database must be consistent before and after the transaction is executed. This means that operations within a transaction must adhere to all constraints and rules defined by the database. In MySQL and PostgreSQL, consistency is achieved by performing operations within transactions. If an operation violates any constraints or rules, the entire transaction will be rolled back.
3. Isolation (Isolation)
   Isolation in the ACID attribute means that each transaction should be isolated from other transactions. This means that one transaction cannot affect the execution results of other transactions. Both MySQL and PostgreSQL support multiple isolation levels, including Read Uncommitted, Read Committed, Repeatable Read and Serializable. The following is an example of MySQL isolation:

SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
BEGIN;
SELECT * FROM users WHERE id = 1;
COMMIT;

In PostgreSQL, you can use the SET TRANSACTION ISOLATION LEVEL command to set the isolation level. The following is an example of PostgreSQL isolation:

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
BEGIN;
SELECT * FROM users WHERE id = 1;
COMMIT;

4. Durability (Durability)
   Durability in ACID attributes refers to that once the transaction is committed, the changes to the database will be permanent and will not be lost even if a system failure occurs. This is achieved by logging all operations and changes in the transaction log. Both MySQL and PostgreSQL use transaction logs to ensure durability.

The above are some of the main features of MySQL and PostgreSQL in terms of ACID properties and transaction management. Different database systems may have slightly different syntax and commands, but the basic principles and concepts are universal.

Summary:
ACID properties and transaction management are crucial concepts in database applications. MySQL and PostgreSQL are two common relational database systems that provide powerful functions and flexibility in terms of ACID properties and transaction management. Developers should choose a suitable database system based on specific needs and scenarios, and use transaction management appropriately to ensure data consistency and durability.

Note: The above examples are for reference only, please modify and use them according to the actual situation.

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