How to perform data concurrency control and conflict resolution operations in MySQL?

How to perform data concurrency control and conflict resolution operations in MySQL?

Introduction:
In most business scenarios, the database is a core component. When multiple concurrent users perform read and write operations on the database at the same time, concurrency control problems and data conflicts may occur in the database. To solve these problems, MySQL provides a variety of concurrency control mechanisms and conflict resolution operations.

1. Concurrency control mechanism:

1. Lock mechanism:
   The lock mechanism in MySQL is used to control access and modification of data. The lock mechanism is divided into shared lock (read lock) and exclusive lock (write lock). Shared locks allow multiple sessions to acquire the lock at the same time for read operations; exclusive locks can only be acquired by one session for write operations.
2. Transaction:
   A transaction is a logical unit of a series of database operations, either all executed successfully or all rolled back. MySQL implements ACID (atomicity, consistency, isolation, and durability) features through the use of transactions to ensure data integrity and consistency.
3. Isolation level:
   MySQL provides four transaction isolation levels, namely read uncommitted, read committed, repeatable read and serialization. The isolation level determines the degree of interaction between transactions and provides different concurrency control capabilities.

2. Conflict resolution operation:

1. Optimistic lock:
   Optimistic lock assumes that no conflicts will occur in most cases of concurrent access, so the data will not be added. Lock. When updating data, use version numbers or timestamps to detect and resolve concurrency conflicts. If a conflict occurs, go back and try again until successful.

Code example:

-- 创建表
CREATE TABLE items (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50),
    quantity INT,
    version INT
);

-- 插入数据
INSERT INTO items (name, quantity, version) VALUES ('item1', 10, 0);

-- 查询数据
SELECT * FROM items WHERE id = 1;

-- 乐观锁更新数据
START TRANSACTION;
    -- 获取当前版本号
    SELECT version INTO @current_version FROM items WHERE id = 1;

    -- 更新数据
    UPDATE items SET quantity = 5, version = version + 1 WHERE id = 1 AND version = @current_version;
    
    -- 检查是否更新成功
    SELECT ROW_COUNT() INTO @affected_rows;
    
    -- 根据更新结果进行处理
    IF @affected_rows = 0 THEN
        -- 冲突处理代码
        -- 重新尝试更新或抛出异常
    ELSE
        -- 提交事务
        COMMIT;
    END IF;

2. Pessimistic lock:
   Pessimistic lock assumes that conflicts will occur in most cases of concurrent access, so the data is locked. By using the SELECT FOR UPDATE statement, an exclusive lock is added to the data to be updated, and other sessions cannot modify the data before acquiring the lock.

Code example:

-- 悲观锁更新数据
START TRANSACTION;
    -- 加锁并查询数据
    SELECT * FROM items WHERE id = 1 FOR UPDATE;
    
    -- 更新数据
    UPDATE items SET quantity = 5 WHERE id = 1;
    
    -- 提交事务
    COMMIT;

Conclusion:
MySQL provides concurrency control mechanisms such as lock mechanism, transaction and isolation level, through optimistic locking and pessimistic locking and corresponding conflict resolution operation, which can effectively solve the conflict problem when accessing the database concurrently. In specific applications, appropriate concurrency control strategies and conflict resolution operations can be selected based on business needs and performance requirements.

(Note: The above code examples are only demonstrations, not specific business codes. In actual application, please modify and adjust according to the specific situation.)

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