needs_rollback flag issue with implementation of backend that does not support savepoint

[Hemant Bhanawat]

I am implementing a backend for Yugabyte. Yugabyte currently doesn't support savepoints. Hence, in the backend, I have set uses_savepoints= False

However, while running the test. I hit the following issue.

The error: "TransactionManagementError: An error occurred in the current transaction. You can't execute queries until the end of the 'atomic' block."

On some investigation, I found that this exception is thrown if self.needs_rollback is True. The first test that uses savepoint passes successfully. However, the second test has needs_rollback set as true and hits this exception.

The problem stems from the following code of enter function in transaction.py

            if self.savepoint and not connection.needs_rollback:
                sid = connection.savepoint()
                connection.savepoint_ids.append(sid)
            else:
                connection.savepoint_ids.append(None)

Basically, a None is inserted in the savepoint_ids when the savepoints are not supported. And the following code in exit function of transaction.py, it sets needs_rollback as true:

                    if sid is None:
                        connection.needs_rollback = True

Can someone please clarify if this is an issue with the code or there is something else that we can do at our layer. For the time being, we have overridden the function savepoint of DatabaseWrapper to return 1. And, we ask the users of our backend to not set savepoint=true in parameters of transaction.atomic().

    def savepoint(self):
             return 1 

[Mariusz Felisiak]

Thanks for this report, however I'm not able to confirm (with the given details) that it is an issue in Django. As far as I'm aware it should work properly. In Django < 2.0 we supported SQLite < 3.7.5 with the same configuration (see 27193aea0088b238e3ee0f0f235364a34a09265c) and it worked fine. You can try to create a topic on the ​https://forum.djangoproject.com or a discussion on DevelopersMailingList.

Feel-free to reopen the ticket when you can provide more details and prove it's an issue in Django.