#32527: needs_rollback flag issue with implementation of backend that does not
support savepoint
-------------------------------------+-------------------------------------
Reporter: Hemant Bhanawat | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution: needsinfo
Keywords: savepoint | Triage Stage:
needs_rollback database backend | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Mariusz Felisiak):
* status: new => closed
* resolution: => needsinfo
Old description:
> 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
New description:
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
}}}
--
Comment:
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.
--
Ticket URL: <https://code.djangoproject.com/ticket/32527#comment:1>
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