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Transaction barriers for Django and Celery.

Project description

django_transaction_barrier provides a barrier-like abstraction for transactions. A Django application developer can use a “transaction barrier” to spawn a task within a transaction and guarantee that the task blocks until it’s able to access the updates made in the transaction. django_transaction_barrier is designed with Celery in mind and provides a Celery task base class. Using the base class it’s easy to write code that atomically modifies the database and spawns a Celery task that executes after the transaction commits.

Installation

Install from source or use pip:

pip install django_transaction_barrier

and add “django_transaction_barrier” to INSTALLED_APPS in settings.py:

INSTALLED_APPS = (
    'django_transaction_barrier',
    ...
)

Usage

from celery import task
from django.db import transaction
from django_transaction_barrier.celery import TransactionBarrierTask

@task(base=TransactionBarrierTask)
def do_something_task(model_id):
  value = Model.objects.get(id=model_id).value
  ...

@transaction.atomic
def kick_off_task(model, value):
    model.value = value
    do_something_task.apply_async_with_barrier(args=(model.id,))
    model.save()

Details

If an application spawns an asynchronous TransactionBarrierTask the task is guaranteed to execute eventually (assuming a durable task queue) after the transaction commits. If the transaction aborts, the task raises a TransactionAborted exception and does not execute. In autocommit mode (i.e., “outside of a transaction”) TransactionBarrierTasks behave like normal Celery tasks.

If an application synchrnously executes a TransactionBarrierTask (e.g., with Celery eager mode) within a transaction, the task executes immediately without waiting for the transaction to commit.

Implementation

django_transaction_barrier implements transaction barriers using row insertion to signify a committed transaction and some DB-specifc logic to detect an abort.

Tests

docker build -t tests . && docker run tests

TODO

  • Add support for a mysql backend.

Project details


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Filename, size & hash SHA256 hash help File type Python version Upload date
django-transaction-barrier-0.3.tar.gz (7.6 kB) Copy SHA256 hash SHA256 Source None Feb 23, 2015

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