wrong sequence of SELECT's and UPDATES in spring-boot-service accessing repository - jpa

Question

i have all simple classes, but i have a problem with the spring-boot-service and the repository.
It's like I have a test class with the following test and the necessary method execut():
#Test
public void deposit() throws Exception {
long balance = accountService.getBalance(accountNr, pin);
execute(() -> accountService.deposit(accountNr, amount), INVOCATIONS);
long newBalance = accountService.getBalance(accountNr, pin);
assertEquals(balance + INVOCATIONS * amount, newBalance);
}
public static void execute(Task task, int times) throws InterruptedException
{
ExecutorService executorService = Executors.newCachedThreadPool();
for (int i = 0; i < times; i++) {
executorService.submit(() -> {
try {
task.run();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
});
}
executorService.shutdown();
executorService.awaitTermination(1, TimeUnit.HOURS);
}
Then there is a very simple entity with four attributes:
#Entity
public class Account {
#Id
#GeneratedValue
private Integer nr;
#Version
private Integer version;
private String pin;
private long balance;
...
The service has a method that first searches for an account, modifies a value, and attempts to store it in the database:
public void deposit(int accountNr, long amount) throws InvalidCredentials, InvalidTransaction {
Account account = accountRepository.getAccountByNr(accountNr);
account.deposit(amount);
accountRepository.saveAndFlush(account);
}
When I now perform the test, the SELECT's and UPDATES are confused, so that the correct value is not in the database at the end.
I then provided the service method with #Transactional(isolation = Isolation.READ_COMMITTED, propagation = Propagation.REQUIRES_NEW), which didn't help either.
Does anyone have an idea?
The log output after spring - banner is:
INFO 20320 --- [ main] o.e.b.a.AccountServiceConcurrentIT : Started AccountServiceConcurrentIT in 9.063 seconds (JVM running for 11.324)
DEBUG 20320 --- [ main] org.hibernate.SQL : select nextval ('hibernate_sequence')
DEBUG 20320 --- [ main] org.hibernate.SQL : insert into account (balance, pin, version, nr) values (?, ?, ?, ?)
DEBUG 20320 --- [ main] org.hibernate.SQL : select account0_.balance as col_0_0_ from account account0_ where account0_.nr=? and account0_.pin=?
DEBUG 20320 --- [pool-1-thread-8] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-2] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-6] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-9] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-2] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-6] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-8] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-4] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-4] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-9] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-3] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-5] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [ool-1-thread-10] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-1] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-7] org.hibernate.SQL : select account0_.nr as nr1_0_, account0_.balance as balance2_0_, account0_.pin as pin3_0_, account0_.version as version4_0_ from account account0_ where account0_.nr=?
DEBUG 20320 --- [pool-1-thread-7] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [ool-1-thread-10] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-5] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-3] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [pool-1-thread-1] org.hibernate.SQL : update account set balance=?, pin=?, version=? where nr=?
DEBUG 20320 --- [ main] org.hibernate.SQL : select account0_.balance as col_0_0_ from account account0_ where account0_.nr=? and account0_.pin=?
java.lang.AssertionError:
Expected :10000
Actual :1000

Answer 1

You are using the ExecutorService to start 10 threads.
These 10 threads are running independently. That means there is no predictable order which thread runs first. As you can see in the log output:
[pool-1-thread-8]
[pool-1-thread-2]
[pool-1-thread-6]
[pool-1-thread-9]
[pool-1-thread-2]
[pool-1-thread-6]
[pool-1-thread-8]
[pool-1-thread-4]
[pool-1-thread-4]
[pool-1-thread-9]
[pool-1-thread-3]
[pool-1-thread-5]
[ool-1-thread-10]
[pool-1-thread-1]
[pool-1-thread-7]
[pool-1-thread-7]
[ool-1-thread-10]
[pool-1-thread-5]
[pool-1-thread-3]
[pool-1-thread-1]
To avoid overwriting of your account balance you must use pessimistic locking.
That can be achieved on the repository with a #Lock annotation:
#Lock(LockModeType.PESSIMISTIC_WRITE)
Account account = accountRepository.getAccountByNr(accountNr);
An you have to make sure that the deposit method is transactional to run all the code in the same transaction:
#Transactional
public void deposit(int accountNr, long amount) throws InvalidCredentials, InvalidTransaction {
Account account = accountRepository.getAccountByNr(accountNr);
account.deposit(amount);
accountRepository.saveAndFlush(account);
}
So every call to getAccountByNr will lock the record and the end of the transaction will release the lock.