MySQL乐观锁和悲观锁的使用与区别

-- 1. 开始事务
START TRANSACTION;

-- 2. 加排他锁（悲观锁）
SELECT * FROM products WHERE id = 1 FOR UPDATE;

-- 3. 执行业务逻辑
UPDATE products SET stock = stock - 1 WHERE id = 1;

-- 4. 提交事务
COMMIT;

-- 表结构增加版本字段
CREATE TABLE products (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    stock INT,
    version INT DEFAULT 0
);

-- 更新时检查版本号
UPDATE products 
SET stock = stock - 1, version = version + 1 
WHERE id = 1 AND version = 1;  -- 这里的1是读取时的版本号

-- 检查影响行数，如果为0表示版本不一致，需要重试

-- 表结构增加时间戳字段
CREATE TABLE products (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    stock INT,
    update_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

-- 更新时检查时间戳
UPDATE products 
SET stock = stock - 1 
WHERE id = 1 AND update_time = '2024-01-01 10:00:00';

-- 基于库存数量判断
UPDATE products 
SET stock = stock - 1 
WHERE id = 1 AND stock > 0;

// Java 示例代码
public boolean deductStockWithRetry(int productId, int quantity) {
    for (int i = 0; i < MAX_RETRY; i++) {
        Product product = productDao.getById(productId);
        if (product.getStock() < quantity) {
            return false; // 库存不足
        }
        int affectedRows = productDao.updateStock(productId, quantity, product.getVersion());
        if (affectedRows > 0) {
            return true; // 更新成功
        }
        // 版本冲突，重试
        Thread.sleep(100); // 短暂等待
    }
    throw new RuntimeException("更新失败，超过最大重试次数");
}

-- 核心业务使用悲观锁
START TRANSACTION;
SELECT * FROM account WHERE user_id = 123 FOR UPDATE;
-- 执行资金操作
COMMIT;
-- 非核心业务使用乐观锁
UPDATE article SET like_count = like_count + 1 
WHERE id = 456 AND version = current_version;