MySQL is throwing deadlock errors, what can I do?¶

Answer: MySQL has default isolation level set to REPEATABLE-READ, if you don’t really need that, set it to READ-COMMITTED. You can do that by adding the following to your my.cnf:

[mysqld]
transaction-isolation = READ-COMMITTED

For more information about InnoDBs transaction model see MySQL - The InnoDB Transaction Model and Locking in the MySQL user manual.

(Thanks to Honza Kral and Anton Tsigularov for this solution)

celeryd is not doing anything, just hanging¶

Answer: See MySQL is throwing deadlock errors, what can I do?.

I’m having IntegrityError: Duplicate Key errors. Why?¶

Answer: See MySQL is throwing deadlock errors, what can I do?. Thanks to howsthedotcom.

Why won’t my Task run?¶

Answer: Did you register the task in the applications tasks.py module? (or in some other module Django loads by default, like models.py?). Also there might be syntax errors preventing the tasks module being imported.

You can find out if the celery daemon is able to run the task by executing the task manually:

>>> from myapp.tasks import MyPeriodicTask
>>> MyPeriodicTask.delay()

Watch celery daemons logfile (or output if not running as a daemon), to see if it’s able to find the task, or if some other error is happening.

Why won’t my Periodic Task run?¶

See Why won’t my Task run?.

Can I send some tasks to only some servers?¶

As of now there is only one use-case that works like this, and that is tasks of type A can be sent to servers x and y, while tasks of type B can be sent to server z. One server can’t handle more than one routing_key, but this is coming in a later release.

Say you have two servers, x, and y that handles regular tasks, and one server z, that only handles feed related tasks, you can use this configuration:

• Servers x and y: settings.py:

AMQP_SERVER = "rabbit"
AMQP_PORT = 5678
AMQP_USER = "myapp"
AMQP_PASSWORD = "secret"
AMQP_VHOST = "myapp"

CELERY_AMQP_CONSUMER_QUEUE = "regular_tasks"
CELERY_AMQP_EXCHANGE = "tasks"
CELERY_AMQP_PUBLISHER_ROUTING_KEY = "task.regular"
CELERY_AMQP_CONSUMER_ROUTING_KEY = "task.#"
CELERY_AMQP_EXCHANGE_TYPE = "topic"

• Server z: settings.py:

AMQP_SERVER = "rabbit"
AMQP_PORT = 5678
AMQP_USER = "myapp"
AMQP_PASSWORD = "secret"
AMQP_VHOST = "myapp"

CELERY_AMQP_CONSUMER_QUEUE = "feed_tasks"
CELERY_AMQP_EXCHANGE = "tasks"
CELERY_AMQP_PUBLISHER_ROUTING_KEY = "task.regular"
CELERY_AMQP_CONSUMER_ROUTING_KEY = "task.feed.#"
CELERY_AMQP_EXCHANGE_TYPE = "topic"

Now to make a Task run on the z server you need to set its routing_key attribute so it starts with the words "task.feed.":

from feedaggregator.models import Feed
from celery.task import Task

class FeedImportTask(Task):
    name = "import_feed"
    routing_key = "task.feed.importer"

    def run(self, feed_url):
        # something importing the feed
        Feed.objects.import_feed(feed_url)

You can also override this using the routing_key argument to celery.task.apply_async():

>>> from celery.task import apply_async
>>> from myapp.tasks import RefreshFeedTask
>>> apply_async(RefreshFeedTask, args=["http://cnn.com/rss"],
...             routing_key="task.feed.importer")