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)
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)
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¶
-
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¶
-
priority
= None¶
-
rate_limit
= None¶
-
reject_on_worker_lost
= None¶
-
request_stack
= <celery.utils.threads._LocalStack object>¶
-
run
(requests)¶ The body of the task executed by workers.
-
serializer
= 'json'¶
-
store_errors_even_if_ignored
= False¶
-
track_started
= False¶
-
typing
= True¶
-
-
class
celery_batches.
SimpleRequest
(id, name, args, kwargs, delivery_info, hostname)¶ Pickleable request.
-
args
= ()¶ positional arguments
-
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
-