Hibernate SpringBoot Prevent Multithread Update - multithreading

Question

I have a counter in database that needs to update to maintain the total number of "downloads". This counter will be updated every time the user downloads a file. The counter is created based on file name. We create a new entry in database if the name is not there with counter value as 1, else update it.
As per the deployment we have two instances of the same applications running.
The problem I am facing is how to prevent the update in case one thread is already updating/creating it.
Thread 1 :
currentCounter = 1
updateOperation = 1 + 1 = 2
Thread 2 (Same Time) :
currentCounter = 1
updateOperation = 1 + 1 = 2
Expected updateOperation = 2 + 1 = 3
This will be a even bigger problem when I have two instances running.

Answer 1

I suggest to use event registration entity
#Entity
public class EventRegistration {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
String eventName;
LocalDateTime happenedAt;
boolean handled;
#Version
Long version;
public EventRegistration(String eventName) {
this.eventName = eventName;
happenedAt = LocalDateTime.now();
handled = false;
}
public void setAsHandled() {
handled = true;
}
// getters, equals, hascode, toString etc...
}
You can create new record of EventRegistration for every event occuarence. Then update counter of event by timer adding number of unhandled EventRegistrations and setting handled = true or even delete handled reconds
#Autowired
EventRegistrationRepository repository;
#Transactional
public void updateEventCounter(String eventName) {
List<EventRegistration> registrations = repository.getAllByEventNameAndHandled(eventName, false);
//update event counter
registrations.forEach(EventRegistration::setAsHandled);
repository.save(registrations);
}