Urd is a scheduler for Django projects. Some features:
- schedule < 1m time slots
- single concurrent execution [1]
- fast enable/disable [2]
- simple deployment
- no extra dependencies beyond Django
| [1] | If tasks take longer to execute than the time to the next execution slot, you get a warning on the next execution. But not simultaneous execution or wild buildup of queues. There is no queue. |
| [2] | It's vitally important to be able to stop a runaway process. With the heartbeat, and with the worker reading the database state before executing, it's easy and fast to disable a job. |
- Install urd
pip install urd - Add
urdtoINSTALLED_APPS - Run
manage.py migrate - Start the scheduler with
manage.py monitor
- Define a
tasks.pymodule in the app that should have tasks. - Create a function like this:
@schedulable_task
def my_task(heartbeat):
for foo in bar:
heartbeat()
do_some_task()Calling heartbeat() regularly is important to make the task cancellable in a timely manner.
Now define a task in the iommi admin. It will be enabled pretty much as soon as you save.
Urd ships with integration for the iommi admin.
- Cron didn't work for me because I need to execute a function more often than once a minute
- Cron also doesn't work for me because if you do once per minute, and the task takes two minutes, you get TWO executing processes of that task for a while. This can be disastrous for a few reasons, and can cause things to spiral out of control.
- Celery/django-q are task queues, not schedulers. They have scheduler components, but they don't have a way to ensure only one process at a time runs a specific task.
- Django-q doesn't allow schedules that execute more often than once per minute
- Django-q caused me a lot of problems where the schedule seemed to put future items in the queue, and I couldn't make it stop trying to execute them.
Urd (or Urðr, or Wyrd) is one of the Norns, the goddesses who weave the destiny of gods and humans.