MySQ中出现幻读问题的解决过程

-- 测试表结构
CREATE TABLE account (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    balance DECIMAL(10,2),
    INDEX idx_balance (balance)
);

-- 测试数据
INSERT INTO account VALUES 
(1, 'Alice', 1000.00),
(2, 'Bob', 2000.00),
(3, 'Charlie', 3000.00);

if (trx_id == creator_trx_id) {
    // 本事务修改的，可见
    return true;
} else if (trx_id < min_trx_id) {
    // 事务已提交，可见
    return true;
} else if (trx_id >= max_trx_id) {
    // 事务还未开始，不可见
    return false;
} else if (trx_id in m_ids) {
    // 事务未提交，不可见
    return false;
} else {
    // 事务已提交，可见
    return true;
}

-- 表中存在记录id=10,20,30
-- 事务A执行：
SELECT * FROM table WHERE id > 15 FOR UPDATE;

-- 锁定的范围包括：
-- (10,20)间隙锁
-- 20记录锁
-- (20,30)间隙锁
-- 30记录锁
-- (30,+∞)间隙锁

import java.sql.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class PhantomReadSolution {
    private static final String URL = "jdbc:mysql://localhost:3306/bank";
    private static final String USER = "root";
    private static final String PASSWORD = "password";
    
    public static void main(String[] args) {
        // 初始化测试数据
        initTestData();
        
        // 创建线程池模拟并发
        ExecutorService executor = Executors.newFixedThreadPool(2);
        
        // 事务A：检查并更新高余额账户
        executor.execute(() -> {
            try (Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)) {
                // 设置为可重复读隔离级别
                conn.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);
                conn.setAutoCommit(false);
                
                System.out.println("【事务A】开始，隔离级别：REPEATABLE_READ");
                
                // 第一次查询：获取高余额账户
                System.out.println("【事务A】第一次查询：余额>1500的账户");
                queryHighBalanceAccounts(conn);
                
                // 模拟处理时间
                Thread.sleep(2000);
                
                // 第二次查询：再次检查
                System.out.println("【事务A】第二次查询：余额>1500的账户");
                queryHighBalanceAccounts(conn);
                
                // 执行更新操作
                System.out.println("【事务A】执行更新：将高余额账户的余额增加10%");
                updateHighBalanceAccounts(conn);
                
                conn.commit();
                System.out.println("【事务A】提交事务");
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        
        // 事务B：插入新账户
        executor.execute(() -> {
            try {
                // 让事务A先开始
                Thread.sleep(500);
                
                try (Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)) {
                    conn.setAutoCommit(false);
                    System.out.println("【事务B】开始");
                    
                    // 插入新账户
                    System.out.println("【事务B】插入新账户：David，余额1800");
                    PreparedStatement stmt = conn.prepareStatement(
                        "INSERT INTO account (name, balance) VALUES (?, ?)");
                    stmt.setString(1, "David");
                    stmt.setDouble(2, 1800.00);
                    stmt.executeUpdate();
                    
                    conn.commit();
                    System.out.println("【事务B】提交事务");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        
        executor.shutdown();
    }
    
    private static void initTestData() {
        try (Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)) {
            Statement stmt = conn.createStatement();
            stmt.execute("DROP TABLE IF EXISTS account");
            stmt.execute("CREATE TABLE account (" +
                         "id INT AUTO_INCREMENT PRIMARY KEY," +
                         "name VARCHAR(50)," +
                         "balance DECIMAL(10,2)," +
                         "INDEX idx_balance (balance))");
            stmt.execute("INSERT INTO account (name, balance) VALUES " +
                         "('Alice', 1000.00), ('Bob', 2000.00), ('Charlie', 3000.00)");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    
    private static void queryHighBalanceAccounts(Connection conn) throws SQLException {
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery(
            "SELECT id, name, balance FROM account WHERE balance > 1500");
        
        System.out.println("高余额账户列表：");
        while (rs.next()) {
            System.out.printf("id=%d, name=%s, balance=%.2f%n",
                rs.getInt("id"), rs.getString("name"), rs.getDouble("balance"));
        }
        rs.close();
        stmt.close();
    }
    
    private static void updateHighBalanceAccounts(Connection conn) throws SQLException {
        // 使用FOR UPDATE加锁，防止幻读影响更新操作
        Statement stmt = conn.createStatement();
        int count = stmt.executeUpdate(
            "UPDATE account SET balance = balance * 1.1 " +
            "WHERE balance > 1500");
        System.out.println("更新了 " + count + " 条记录");
        stmt.close();
    }
}

START TRANSACTION;
-- 快照读
SELECT * FROM account WHERE balance > 1500; -- 看到2条记录

-- 其他事务插入新记录并提交

-- 当前读
SELECT * FROM account WHERE balance > 1500 FOR UPDATE; -- 看到3条记录
-- 此时事务内看到了"幻影行"

-- 添加版本号字段
ALTER TABLE account ADD COLUMN version INT DEFAULT 0;

-- 乐观锁更新
UPDATE account 
SET balance = balance * 1.1, version = version + 1
WHERE balance > 1500 AND version = #{oldVersion};