Hi,
I believe that I encountered a bug or at least a serious limitation with
transaction.on_commit in Django 1.9.x. Essentially, the on_commit hooks
seem to be tied to the database connection instead of the transaction. This
means that unrelated transactions may trigger on_commit hooks, which
results in undesired execution order. Here is an example:
from django.db import transaction
from foobar.models import Model1, Model2
@transaction.atomic
def outer():
print("START - OUTER")
for i in range(4):
f1(i)
print("END - OUTER")
@transaction.atomic
def f1(i):
model = Model1(description="test {0}".format(i))
model.save()
transaction.on_commit(lambda: commit_hook(model, i))
def commit_hook(model, i):
print("START - on_commit hook")
f2(i)
print("STOP - on_commit hook")
@transaction.atomic
def f2(i):
print("CALLING F2")
model = Model2(description="test {0}".format(i))
model.save()
Some quick explanations:
- outer is the outermost atomic block. f1 will only create a savepoint().
This works as expected, there is only one commit (trace erased for
simplicity).
- f2 is wrapped in an "outermost" atomic block and indeed, f2 will be
called four times and there will be four commits (trace erased for
simplicity).
- f1 register a commit_hook. I expect that at the end of outer(), all
commit hooks will be called.
The expected trace is:
START - OUTER
END - OUTER
START - on_commit hook
CALLING F2
STOP - on_commit hook
START - on_commit hook
CALLING F2
STOP - on_commit hook
START - on_commit hook
CALLING F2
STOP - on_commit hook
START - on_commit hook
CALLING F2
STOP - on_commit hook
The actual trace (f2 is triggering the on_commit hooks registered in
f1/outer):
START - OUTER
END - OUTER
START - on_commit hook
CALLING F2
START - on_commit hook
CALLING F2
START - on_commit hook
CALLING F2
START - on_commit hook
CALLING F2
STOP - on_commit hook
STOP - on_commit hook
STOP - on_commit hook
STOP - on_commit hook
I wanted to know if someone encountered this issue or if I am
misunderstanding on_commit before opening a ticket.
Regards,
Bart
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