Question

I am trying to implement a basic optimistic lock mechanism with a retry interceptor.

So the thing is there is a object Quiz with a property responsesCount. In case that there is a optimistic Lock exception thrown during an update of the quiz, the respective update method will be invoked again from the retry interceptor.

The thing is that something is not right because the retried method has the same version number number every time, and because of this it will fail the transaction no matter what.

version: 10

process A:
start update quiz, version 10
process B:
start update quiz, version 10
process B:
finish update quiz, version 11
process A:
optimistic exception thrown raised update quiz, retry process A
inside the retried method the version is always 10

What can I do then? It should increment automatically the version in order to success the transaction

Answer 1

An optimistic lock exception is handled like this:

First re-read the record, getting the new version number and the updated field values which the conflicting transaction wrote.

Then reapply your operation, based on the new values.
In your case this is simple — incrementing a value is order-independent or commutative. Other operations might not be simple to reapply — for example, suppose the transactions were both trying to move a bug in an issue tracker from one workflow state to another. This transition can only happen once, so the retrying transaction would need to check that the bug was still in a valid state for that transition, and if not it would report an error to the user.