How to implement transaction processing in MySQL?

How to implement transaction processing in MySQL?

Transaction is one of the important concepts in the database, which can ensure the consistency and integrity of data and the correctness of data in concurrent operations. As a commonly used relational database, MySQL also provides a transaction processing mechanism.

1. Characteristics of transactions

Transactions have the following four characteristics, which are usually summarized by ACID: Atomicity, Consistency, Isolation, and Durability (Durability).

1. Atomicity: A transaction is an indivisible unit of work. Either all executions are successful or none are executed. There will be no partial execution success and partial execution failure.
2. Consistency: The data in the database should remain consistent before and after transaction execution. During the execution of a transaction, data may be modified, deleted, or added, but after the transaction is submitted, the consistency of the data should be guaranteed.
3. Isolation: Transactions should be isolated from each other, that is, the execution of one transaction should not affect other transactions. Each transaction can only see the data before submission of other transactions, but not the uncommitted data.
4. Persistence: Once a transaction is committed, its modifications to the database should be permanent and should not be lost even when the database fails.

2. The use of transactions

MySQL provides two ways to handle transactions: implicit transactions and explicit transactions.

1. Implicit transaction: When a SQL statement is executed, MySQL will automatically encapsulate it into a transaction and commit or rollback it. This method is suitable for executing a single statement or when there is no dependency between multiple statements.

For example, executing the following statement will automatically start a transaction:

INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);

2. Explicit transaction: Control the submission or completion of the transaction by manually specifying the start and end of the transaction. rollback.

The start of a transaction uses the START TRANSACTION statement. The end of the transaction can be used to commit the transaction using COMMIT or use ROLLBACK to roll back the transaction.

START TRANSACTION;
UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE condition;
COMMIT;

In an explicit transaction, you can use the ROLLBACK statement to roll back the entire transaction. You can also use the SAVEPOINT and ROLLBACK TO SAVEPOINT statements to roll back the entire transaction. Setup and rollback to savepoint.

3. Transaction isolation level

The isolation level of a transaction determines the degree of mutual influence between transactions. MySQL provides four isolation levels: Read Uncommitted, Read Committed (Read Committed), Repeatable Read (Repeatable Read) and Serializable (Serializable).

1. Uncommitted read: One transaction can read uncommitted data of another transaction, which may cause dirty reads, non-repeatable reads, and phantom reads.
2. Committed read: A transaction can only read data that has been submitted by another transaction, but it may cause non-repeatable reads and phantom reads.
3. Repeatable reading: The reading results of the same row of data during a transaction are consistent during execution, which can prevent dirty reads and non-repeatable reads, but may lead to phantom reads.
4. Serialization: All transactions are executed in order, which can solve the problems of dirty reads, non-repeatable reads and phantom reads, but it will lead to a decrease in concurrency performance.

4. Things to note about transactions

When using transactions, you need to pay attention to the following points:

1. Minimize the holding time of transactions: Transactions The longer the database lock is held, the longer other transactions need to wait, affecting concurrency performance.
2. Do not perform long-term operations in a transaction: If you perform a long-term operation in a transaction, it will cause other transactions to wait for a long time and reduce concurrency performance.
3. Try to use a lower isolation level: a higher isolation level will cause more locks, resulting in reduced concurrency performance.
4. Use an appropriate transaction size: A transaction that is too large may cause locks to be held for a long time, and a transaction that is too small may cause frequent opening and submission of transactions, affecting performance.

In short, to implement transaction processing in MySQL, you need to understand the characteristics, usage and isolation levels of transactions, and apply them appropriately according to the specific situation. Through reasonable use of transactions, the consistency and integrity of data in the database can be ensured, and the concurrency and stability of the system can be improved.

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