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?.

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")