Djangocon EU: where did it all BEGIN;? Django’s transaction management - Charlie Denton & Sam Searles-Bryant¶

Tags: django, djangocon

(One of my summaries of the 2026 Djangocon EU in Athens).

Transactions are an SQL concept. You “begin” a transaction, do a bunch of statements and at the end “commit” it. Only then does it actually show up in the database for other connections:

BEGIN;
  INSERT ...;
  UPDATE ...;
  INSERT ...;
COMMIT;

If something goes wrong, you can abort it with “rollback”:

BEGIN;
  INSERT ...;
  UPDATE ...;
  INSERT ...;
ROLLBACK;

The SQL default is to run in “autocommit” mode, so everything always updates the database immediately.

The history of Django’s transaction management:

• <0.95 emulated sql’s autocommit by executing COMMIT; after every save.

• 0.95 introduced with commit_on_success():, which would give you a context manager, at the end everything would be committed unless an error occurred. It did have a corner case: you couldn’t really nest commit_on_success.

• 1.6 introduced with atomic():, mostly like commit_on_success, but it introduced SAVEPOINT, allowing you to rollback a nested .atomic() to the savepoint that’s created when you enter a nested ‘atomic’ block.

• 3.2 introduced with atomic(durable=True):. If you had a nested atomic, a transaction you thought was committed might be rolled back by another ‘atomic’ wrapping the code. When you specify durable=True, calling ‘atomic’ fails with an error, as it isn’t legal in this case.

In their own projects they sometimes wanted to have more explicit control. They sometimes had a check like if assert not connection.in_atomic_block, but that didn’t look nice. They split atomic() into separate transaction(), savepoint() and durable() context managers. Nicely explicit.

The code is here: https://github.com/kraken-tech/django-subatomic

A big inspiration for them was a talk by Aymeric Augustin at the 2013 djangocon.eu. Here’s my summary of that talk.

Unrelated photo explanation: a cat I encountered in Athens on an evening stroll in the neighbourhood behind the hotel.