Spring Data JPA : A transaction with isolation READ_COMMITTED does not see data committed in another transaction

Question

So, I have a very simple Spring Boot-based web application.

The database has one table, user , with columns id and username and one record: (1, 'Joe') .

I also have the following classes:

User - an entity mapped to the table user

UserRepository - a Spring Data JPA repository for it

UserService + DefaultUserService - a service layer with CRUD methods

UserController - a controller with two methods: get and update

Application - the main class (with @EnableTransactionManagement annotation on it)

So, what I'm trying to do is to test transaction isolation level READ_COMMITTED . I'm sending two simultaneous requests:

1. To /update , which updates a user, setting its name to Jack , then puts a current thread to sleep for 5s and then commits the transaction.
2. To /get , which repeatedly reads the same user for 10 times making a nap for 1s after every attempt.

The issue is that even after the transaction for (1) has been committed, (2) keeps returning an old value - Joe . If I try to send another request to /get after that, it returns Jack , as expected, so the issue happens only if transaction (2) has started before transaction (1) has committed a change to the DB.

You may find some code for reference below.

Service:

@Service
public class DefaultUserService implements UserService {

    ... //fields & constructor

    @Override
    @SneakyThrows
    @Transactional(isolation = Isolation.READ_COMMITTED)
    public User read(Long id) {
        User user = userRepository.findById(id).get();
        Thread.sleep(1000);
        return user;
    }

    @Override
    @SneakyThrows
    @Transactional
    public User update(Long id, User update) {
        log.info("Entering update method for user {}", id);
        User user = read(id);

        user.setUsername("Jack");
        user = userRepository.save(user);

        log.info("User {} updated, falling asleep for 5s", id);
        Thread.sleep(5000);

        return user;
    }
}

Controller:

@RestController
public class UserController {

    ... //fields & constructor

    @RequestMapping("/update")
    public User update() {
        User user = userService.update(1L, new User("Jack"));
        log.info("UPDATED: {}", user);
        return user;
    }

    @RequestMapping("/get")
    public User get() {
        User user = userService.read(1L);
        for (int i = 0; i < 10; i++) {
            log.info("READ: {}", user);
            user = userService.read(1L);
        }
        return user;
    }
}    

Log output:

04:37:52.915 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:53.151 [nio-8781-exec-1] Entering update method for user 1
04:37:53.919 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:54.152 [nio-8781-exec-1] User 1 updated, falling asleep for 5s
04:37:54.922 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:55.926 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:56.932 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:57.937 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:58.943 [io-8781-exec-10] READ: ID: 1 :: Joe
04:37:59.222 [nio-8781-exec-1] UPDATED: ID: 1 :: Jack
04:37:59.947 [io-8781-exec-10] READ: ID: 1 :: Joe
04:38:00.950 [io-8781-exec-10] READ: ID: 1 :: Joe
04:38:01.956 [io-8781-exec-10] READ: ID: 1 :: Joe

Responses returned by controllers are also different. For /update it's:

{"id":1,"username":"Jack"}

While for /get :

{"id":1,"username":"Joe"}

I'm using MySQL 5.7.18 and Spring Boot 2.1.0.

Any ideas about what I might be doing wrong/missing? Thanks in advance.

Answer 1

Your code works correctly with Oracle but with MySQL its bit different. Read here about isolation levels in MySql

https://blog.pythian.com/understanding-mysql-isolation-levels-repeatable-read/

I believe if you change isolation level of your method to Read committed it should work as by default MySql has Repeatable-read which is handled bit differntly.

   @Transactional(Isolation.READ_COMMITTED)
    public User update(Long id, User update) 

Answer 2

Set:

@Override
@SneakyThrows
@Transactional(propagation = Propagation.REQUIRES_NEW, isolation = Isolation.READ_COMMITTED)
public User read(Long id) {
    User user = userRepository.findById(id).get();
    Thread.sleep(1000);
    return user;
}