celery parallel tasking error 'no result backend configured'

Question

Running django-celery 3.1.16, Celery 3.1.17, Django 1.4.16. Trying to run some parallel tasks using 3 workers and collect the results using the following:

from celery import group

positions = []
jobs = group(celery_calculate_something.s(data.id) for data in a_very_big_list)
results = jobs.apply_async()
positions.extend(results.get())

The task celery_calculate_something returns an object to place the in the results list:

app.task(ignore_result=False)
def celery_calculate_something(id):
  <do stuff>

No matter what I try, I always get the same result when calling get() on results:

No result backend configured.  Please see the documentation for more information.

However, the results backend IS configured - I have many other tasks with ignore_result=False merrily adding to the tasks meta table in django_celery. It is something to do with using the results returned from group(). I should note it is not set explicitly in settings - it seems that django-celery has set it automatically for you.

I have the worker collecting events using:

manage.py celery worker -l info -E

and celerycam running with

python manage.py celerycam

Inspecting the results object returned (an instance of GroupResult) I can see that the backend attr is an instance of DisabledBackend. Is this the problem? What have I mis-understood?

Dan · Accepted Answer · 2015-05-20 09:49:23Z

You did not configure the results backend, so basically you need tables to store the results, since you have django-celery add it to INSTALLED_APPS in your settings.py file and then perform the migration (python manage.py migrate) After that open your celery.py file and modify your backend to djcelery.backends.database:DatabaseBackend.
Here's an example

app = Celery('almanet',
 broker='amqp://guest@localhost//',
 backend='djcelery.backends.database:DatabaseBackend',
 include=['alm_crm.tasks'] #References your tasks. Donc forget to put the whole absolute path.
 )

After that you can import results from celery import result Now you can save the result and extract the result by job.id

from celery import group
positions = []
jobs = group(celery_calculate_something.s(data.id) for data in
a_very_big_list)
results = jobs.apply_async()
results.save()
some_task_result = result.GroupResult.restore(results.id)
print some_task_results.ready()

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