Spring Boot 事务隔离级别

Question

我有这个项目试图检查事务隔离。我从 READ_UNCOMMITTED 级别开始，但它不起作用。 代码非常简单。

主类

@SpringBootApplication
@EnableTransactionManagement
public class HibernateTransactionsLocksTestApplication {

    public static void main(String[] args) {
        SpringApplication.run(HibernateTransactionsLocksTestApplication.class, args);
    }

}

控制器

    @RestController
    public class HomeController {

        private final AccountService accountService;

        public HomeController(AccountService accountService) {
            this.accountService = accountService;
        }

        @GetMapping("/updateAccount2RU")
        public String updateAccount2RU() throws InterruptedException {
            accountService.updateAccount2RU();
            return "done!";
        }

        @GetMapping("/update2Account2RU")
        public String update2Account2RU() throws InterruptedException {
            accountService.update2Account2RU();
            return "done!";
        }
}

服务

@Service
public class AccountService {

    private final AccountRepository accountRepository;

    public AccountService(AccountRepository accountRepository) {
        this.accountRepository = accountRepository;
    }

    @Transactional(isolation = Isolation.READ_UNCOMMITTED)
    public void updateAccount2RU() throws InterruptedException {
        Account a = accountRepository.findById(2).get();
        System.out.println("Account amount: " + a.getAmount());
        a.setAmount(a.getAmount()+1);
        accountRepository.save(a);
        Thread.currentThread().sleep(5000);
    }

    @Transactional(isolation = Isolation.READ_UNCOMMITTED)
    public void update2Account2RU() throws InterruptedException {
        Account a = accountRepository.findById(2).get();
        System.out.println("Account amount: " + a.getAmount());
        a.setAmount(a.getAmount()+1);
        Thread.currentThread().sleep(5000);
    }

}

Repository 是一个简单的 SpringData 存储库

@Repository
public interface AccountRepository extends JpaRepository<Account, Integer> {

    @Transactional(propagation = Propagation.MANDATORY, isolation = Isolation.READ_UNCOMMITTED)
    Account findByName(String name);
}

application.properties

server.contextPath=/

spring.datasource.url=jdbc:mysql://localhost:3306/trasactions-locks-tests
spring.datasource.username=
spring.datasource.password=
spring.jpa.properties.hibernate.dialect =org.hibernate.dialect.MySQL5Dialect

spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
#spring.jpa.properties.hibernate.format_sql=true
logging.level.org.hibernate.SQL=DEBUG
logging.level.org.hibernate.type.descriptor.sql.BasicBinder=TRACE

spring.jpa.open-in-view=false

#Check transactions behaviour
logging.level.org.springframework.transaction.interceptor=TRACE

基本上我在 Chrome 中打开 2 个选项卡并访问 updateAccount2RU（这应该读取帐户并增加金额，线程应该在醒来并提交事务之前休眠 5 秒）同时我访问第二种方法 update2Account2RU读取相同的帐户，并且从第一种方法读取的金额相同，而不是更新的方法。

Answer 1

您很可能需要在第一种方法中使用accountRepository.save(a);。

SQL 更新通常由 Hibernate 缓冲，直到事务提交时，即当您的事务方法返回时。

因此，在 T2 读取记录时，没有挂起的未提交数据库更改。

@Transactional(isolation = Isolation.READ_UNCOMMITTED)
public void updateAccount2RU() throws InterruptedException {
    Account a = accountRepository.findById(2).get();
    System.out.println("Account amount: " + a.getAmount());
    a.setAmount(a.getAmount()+1);

    // force explicit flush so T2 should now see the uncommitted change
    accountRepository.saveAndFlush(a);

    Thread.currentThread().sleep(5000);
}

见：

https://docs.jboss.org/hibernate/stable/core.old/reference/en/html/objectstate-flushing.html

Session 会不时执行所需的 SQL 语句 将 JDBC 连接的状态与对象的状态同步 保存在记忆中。这个过程，flush，默认发生在 以下几点

• 在一些查询执行之前
• 来自 org.hibernate.Transaction.commit()
• 来自 Session.flush()