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I have a test queue in celery and I have defined a task for it:
@celery_app.task(queue='test', ignore_result=True)
def priority_test(priority):
print(priority)
which just print the argument.I want to set the priority attribute which is defined here for appy_async. So, I wrote a for loop like this:
for i in range(100):
priority_test.apply_async((i%10,), queue="test", priority=i%10)
I excpected to see some result like this:
[2017-12-26 17:21:37,309: WARNING/ForkPoolWorker-1] 10
[2017-12-26 17:21:37,311: WARNING/ForkPoolWorker-1] 10
[2017-12-26 17:21:37,314: WARNING/ForkPoolWorker-1] 10
[2017-12-26 17:21:37,317: WARNING/ForkPoolWorker-1] 9
[2017-12-26 17:21:37,319: WARNING/ForkPoolWorker-1] 9
[2017-12-26 17:21:37,321: WARNING/ForkPoolWorker-1] 9
[2017-12-26 17:21:37,323: WARNING/ForkPoolWorker-1] 8
[2017-12-26 17:21:37,326: WARNING/ForkPoolWorker-1] 8
[2017-12-26 17:21:37,329: WARNING/ForkPoolWorker-1] 8
[2017-12-26 17:21:37,332: WARNING/ForkPoolWorker-1] 7
[2017-12-26 17:21:37,334: WARNING/ForkPoolWorker-1] 7
[2017-12-26 17:21:37,336: WARNING/ForkPoolWorker-1] 7
[2017-12-26 17:21:37,341: WARNING/ForkPoolWorker-1] 6
[2017-12-26 17:21:37,344: WARNING/ForkPoolWorker-1] 6
[2017-12-26 17:21:37,346: WARNING/ForkPoolWorker-1] 6
[2017-12-26 17:21:37,349: WARNING/ForkPoolWorker-1] 5
[2017-12-26 17:21:37,351: WARNING/ForkPoolWorker-1] 5
[2017-12-26 17:21:37,353: WARNING/ForkPoolWorker-1] 5
[2017-12-26 17:21:37,355: WARNING/ForkPoolWorker-1] 4
[2017-12-26 17:21:37,358: WARNING/ForkPoolWorker-1] 4
[2017-12-26 17:21:37,360: WARNING/ForkPoolWorker-1] 4
means execute the same priorities after each other but it executed them in the normal way:
[2017-12-26 17:21:37,309: WARNING/ForkPoolWorker-1] 10
[2017-12-26 17:21:37,311: WARNING/ForkPoolWorker-1] 9
[2017-12-26 17:21:37,314: WARNING/ForkPoolWorker-1] 8
[2017-12-26 17:21:37,317: WARNING/ForkPoolWorker-1] 7
[2017-12-26 17:21:37,319: WARNING/ForkPoolWorker-1] 6
[2017-12-26 17:21:37,321: WARNING/ForkPoolWorker-1] 5
[2017-12-26 17:21:37,323: WARNING/ForkPoolWorker-1] 4
[2017-12-26 17:21:37,326: WARNING/ForkPoolWorker-1] 3
[2017-12-26 17:21:37,329: WARNING/ForkPoolWorker-1] 2
[2017-12-26 17:21:37,332: WARNING/ForkPoolWorker-1] 1
[2017-12-26 17:21:37,334: WARNING/ForkPoolWorker-1] 10
[2017-12-26 17:21:37,336: WARNING/ForkPoolWorker-1] 9
[2017-12-26 17:21:37,341: WARNING/ForkPoolWorker-1] 8
[2017-12-26 17:21:37,344: WARNING/ForkPoolWorker-1] 7
[2017-12-26 17:21:37,346: WARNING/ForkPoolWorker-1] 6
[2017-12-26 17:21:37,349: WARNING/ForkPoolWorker-1] 5
[2017-12-26 17:21:37,351: WARNING/ForkPoolWorker-1] 4
[2017-12-26 17:21:37,353: WARNING/ForkPoolWorker-1] 3
[2017-12-26 17:21:37,355: WARNING/ForkPoolWorker-1] 2
[2017-12-26 17:21:37,358: WARNING/ForkPoolWorker-1] 1
[2017-12-26 17:21:37,360: WARNING/ForkPoolWorker-1] 10
[2017-12-26 17:21:37,362: WARNING/ForkPoolWorker-1] 9
[2017-12-26 17:21:37,364: WARNING/ForkPoolWorker-1] 8
[2017-12-26 17:21:37,365: WARNING/ForkPoolWorker-1] 7
[2017-12-26 17:21:37,367: WARNING/ForkPoolWorker-1] 6
[2017-12-26 17:21:37,369: WARNING/ForkPoolWorker-1] 5
[2017-12-26 17:21:37,371: WARNING/ForkPoolWorker-1] 4
[2017-12-26 17:21:37,373: WARNING/ForkPoolWorker-1] 3
[2017-12-26 17:21:37,374: WARNING/ForkPoolWorker-1] 2
[2017-12-26 17:21:37,376: WARNING/ForkPoolWorker-1] 1
How should I apply priority in celery with rabbitmq and what is the priority attribute in the doc above?
751
apply_async(args[, kwargs[, …]]) Sends a task message. delay(*args, **kwargs) Shortcut to send a task message, but doesn't support execution options. calling ( __call__ )
Python solves this by using a binary heap to implement the priority queue. The Python priority queue is built on the heapq module, which is basically a binary heap. The get command dequeues the highest priority elements from the queue.
Process of Task Execution by Celery can be broken down into:Your application sends the tasks to the task broker, it is then reserved by a worker for execution & finally the result of task execution is stored in the result backend.
Celery communicates via messages, usually using a broker to mediate between clients and workers. To initiate a task, the Celery client adds a message to the queue, and the broker then delivers that message to a worker. The most commonly used brokers are Redis and RabbitMQ.
In order to have priority working properly you need to properly configure a couple of settings and you need at least version 3.5.0 of RabbitMQ.
First set the x-max-priority of your queue to 10. From the docs :
from kombu import Exchange, Queue
app.conf.task_queues = [
Queue('tasks', Exchange('tasks'), routing_key='tasks',
queue_arguments={'x-max-priority': 10},
]
A default value for all queues can be set using the task_queue_max_priority setting:
app.conf.task_queue_max_priority = 10
Then configure the following settings:
CELERY_ACKS_LATE = True
CELERYD_PREFETCH_MULTIPLIER = 1
By default the prefetch multiplier is 4, which in your case will cause the first 4 tasks with priority 10, 9, 8 and 7 to be fetched before the other tasks are present in the queue. The CELERY_ACKS_LATE setting will cause the tasks to be acknowledged after they have been executed. You can experiment with this setting to see what behaviour you prefer.
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