celery_batches

Experimental task class that buffers messages and processes them as a list. Task requests are buffered in memory (on a worker) until either the flush count or flush interval is reached. Once the requests are flushed, they are sent to the task as a list of SimpleRequest instances.

It is possible to return a result for each task request by calling mark_as_done on your results backend. Returning a value from the Batch task call is only used to provide values to signals and does not populate into the results backend.

Warning

For this to work you have to set worker_prefetch_multiplier to zero, or some value where the final multiplied value is higher than flush_every. Note that Celery will attempt to continually pull data into memory if this is set to zero. This can cause excessive resource consumption on both Celery workers and the broker when used with a deep queue.

In the future we hope to add the ability to direct batching tasks to a channel with different QoS requirements than the task channel.

Simple Example

A click counter that flushes the buffer every 100 messages, and every 10 seconds. Does not do anything with the data, but can easily be modified to store it in a database.

# Flush after 100 messages, or 10 seconds.
@app.task(base=Batches, flush_every=100, flush_interval=10)
def count_click(requests):
    from collections import Counter
    count = Counter(request.kwargs['url'] for request in requests)
    for url, count in count.items():
        print('>>> Clicks: {0} -> {1}'.format(url, count))

Then you can ask for a click to be counted by doing:

>>> count_click.delay('http://example.com')

Example returning results

An interface to the Web of Trust API that flushes the buffer every 100 messages, and every 10 seconds.

import requests
from urlparse import urlparse

from celery_batches import Batches

wot_api_target = 'https://api.mywot.com/0.4/public_link_json'

@app.task(base=Batches, flush_every=100, flush_interval=10)
def wot_api(requests):
    sig = lambda url: url
    reponses = wot_api_real(
        (sig(*request.args, **request.kwargs) for request in requests)
    )
    # use mark_as_done to manually return response data
    for response, request in zip(reponses, requests):
        app.backend.mark_as_done(request.id, response, request=request)


def wot_api_real(urls):
    domains = [urlparse(url).netloc for url in urls]
    response = requests.get(
        wot_api_target,
        params={'hosts': ('/').join(set(domains)) + '/'}
    )
    return [response.json[domain] for domain in domains]

Using the API is done as follows:

>>> wot_api.delay('http://example.com')

Note

If you don’t have an app instance then use the current app proxy instead:

from celery import current_app
current_app.backend.mark_as_done(request.id, response, request=request)

API

class celery_batches.Batches

Strategy(task, app, consumer)

str(object=’’) -> str str(bytes_or_buffer[, encoding[, errors]]) -> str

Create a new string object from the given object. If encoding or errors is specified, then the object must expose a data buffer that will be decoded using the given encoding and error handler. Otherwise, returns the result of object.__str__() (if defined) or repr(object). encoding defaults to sys.getdefaultencoding(). errors defaults to ‘strict’.

abstract = True

Deprecated attribute abstract here for compatibility.

apply(args=None, kwargs=None, *_args, **_kwargs)

Execute this task locally as a batch of size 1, by blocking until the task returns.

Arguments:

args (Tuple): positional arguments passed on to the task.

Returns:

celery.result.EagerResult: pre-evaluated result.

apply_buffer(requests, args=(), kwargs={})

flush(requests)

flush_every = 10

Maximum number of message in buffer.

flush_interval = 30

Timeout in seconds before buffer is flushed anyway.

ignore_result = False

If enabled the worker won’t store task state and return values for this task. Defaults to the task_ignore_result setting.

priority = None

Default task priority.

rate_limit = None

Rate limit for this task type. Examples: None (no rate limit), ‘100/s’ (hundred tasks a second), ‘100/m’ (hundred tasks a minute),`’100/h’` (hundred tasks an hour)

reject_on_worker_lost = None

Even if acks_late is enabled, the worker will acknowledge tasks when the worker process executing them abruptly exits or is signaled (e.g., :sig:`KILL`/:sig:`INT`, etc).

Setting this to true allows the message to be re-queued instead, so that the task will execute again by the same worker, or another worker.

Warning: Enabling this can cause message loops; make sure you know what you’re doing.

request_stack = <celery.utils.threads._LocalStack object>

Task request stack, the current request will be the topmost.

run(requests)

The body of the task executed by workers.

serializer = 'json'

The name of a serializer that are registered with kombu.serialization.registry. Default is ‘json’.

store_errors_even_if_ignored = False

When enabled errors will be stored even if the task is otherwise configured to ignore results.

track_started = False

If enabled the task will report its status as ‘started’ when the task is executed by a worker. Disabled by default as the normal behavior is to not report that level of granularity. Tasks are either pending, finished, or waiting to be retried.

Having a ‘started’ status can be useful for when there are long running tasks and there’s a need to report what task is currently running.

The application default can be overridden using the task_track_started setting.

typing = True

Enable argument checking. You can set this to false if you don’t want the signature to be checked when calling the task. Defaults to app.strict_typing.

class celery_batches.SimpleRequest(id, name, args, kwargs, delivery_info, hostname, reply_to, correlation_id)

A request to execute a task.

A list of SimpleRequest instances is provided to the batch task during execution.

This must be pickleable (if using the prefork pool), but generally should have the same properties as Request.

args = ()

positional arguments

chord = None

TODO

correlation_id = None

used similarly to reply_to

delivery_info = None

message delivery information.

classmethod from_request(request)

hostname = None

worker node name

id = None

task id

kwargs = {}

keyword arguments

name = None

task name

reply_to = None

used by rpc backend when failures reported by parent process