rq-scheduler-bcfg

============ RQ Scheduler

RQ Scheduler <https://github.com/rq/rq-scheduler>_ is a small package that adds job scheduling capabilities to RQ <https://github.com/nvie/rq>, a Redis <http://redis.io/> based Python queuing library.

.. image:: https://travis-ci.org/rq/rq-scheduler.svg?branch=master :target: https://travis-ci.org/rq/rq-scheduler

============ Requirements

• RQ_

============ Installation

You can install RQ Scheduler_ via pip::

pip install rq-scheduler

Or you can download the latest stable package from PyPI <http://pypi.python.org/pypi/rq-scheduler>_.

===== Usage

Schedule a job involves doing two different things:

1. Putting a job in the scheduler
2. Running a scheduler that will move scheduled jobs into queues when the time comes

---

Scheduling a Job

There are two ways you can schedule a job. The first is using RQ Scheduler's enqueue_at

.. code-block:: python

from redis import Redis
from rq import Queue
from rq_scheduler import Scheduler
from datetime import datetime

scheduler = Scheduler(connection=Redis()) # Get a scheduler for the "default" queue

# You can also instantiate a Scheduler using an RQ Queue
queue = Queue('foo', connection=Redis())
scheduler = Scheduler(queue=queue)

# Puts a job into the scheduler. The API is similar to RQ except that it
# takes a datetime object as first argument. So for example to schedule a
# job to run on Jan 1st 2020 we do:
scheduler.enqueue_at(datetime(2020, 1, 1), func) # Date time should be in UTC

# Here's another example scheduling a job to run at a specific date and time (in UTC),
# complete with args and kwargs.
scheduler.enqueue_at(datetime(2020, 1, 1, 3, 4), func, foo, bar=baz)

The second way is using enqueue_in. Instead of taking a datetime object, this method expects a timedelta and schedules the job to run at X seconds/minutes/hours/days/weeks later. For example, if we want to monitor how popular a tweet is a few times during the course of the day, we could do something like

.. code-block:: python

from datetime import timedelta

# Schedule a job to run 10 minutes, 1 hour and 1 day later
scheduler.enqueue_in(timedelta(minutes=10), count_retweets, tweet_id)
scheduler.enqueue_in(timedelta(hours=1), count_retweets, tweet_id)
scheduler.enqueue_in(timedelta(days=1), count_retweets, tweet_id)

IMPORTANT: You should always use UTC datetime when working with RQ Scheduler_.

---

Periodic & Repeated Jobs

As of version 0.3, RQ Scheduler_ also supports creating periodic and repeated jobs. You can do this via the schedule method. Note that this feature needs RQ_ >= 0.3.1.

This is how you do it

.. code-block:: python

scheduler.schedule(
    scheduled_time=datetime.utcnow(), # Time for first execution, in UTC timezone
    func=func,                     # Function to be queued
    args=[arg1, arg2],             # Arguments passed into function when executed
    kwargs={'foo': 'bar'},         # Keyword arguments passed into function when executed
    interval=60,                   # Time before the function is called again, in seconds
    repeat=10,                     # Repeat this number of times (None means repeat forever)
    meta={'foo': 'bar'}            # Arbitrary pickleable data on the job itself
)

IMPORTANT NOTE: If you set up a repeated job, you must make sure that you either do not set a result_ttl value or you set a value larger than the interval. Otherwise, the entry with the job details will expire and the job will not get re-scheduled.

---

Cron Jobs

As of version 0.6.0, RQ Scheduler_ also supports creating Cron Jobs, which you can use for repeated jobs to run periodically at fixed times, dates or intervals, for more info check https://en.wikipedia.org/wiki/Cron. You can do this via the cron method.

This is how you do it

.. code-block:: python

scheduler.cron(
    cron_string,                # A cron string (e.g. "0 0 * * 0")
    func=func,                  # Function to be queued
    args=[arg1, arg2],          # Arguments passed into function when executed
    kwargs={'foo': 'bar'},      # Keyword arguments passed into function when executed
    repeat=10,                  # Repeat this number of times (None means repeat forever)
    queue_name=queue_name,      # In which queue the job should be put in
    meta={'foo': 'bar'}         # Arbitrary pickleable data on the job itself
)

---

Retrieving scheduled jobs

Sometimes you need to know which jobs have already been scheduled. You can get a list of enqueued jobs with the get_jobs method

.. code-block:: python

list_of_job_instances = scheduler.get_jobs()

In it's simplest form (as seen in the above example) this method returns a list of all job instances that are currently scheduled for execution.

Additionally the method takes two optional keyword arguments until and with_times. The first one specifies up to which point in time scheduled jobs should be returned. It can be given as either a datetime / timedelta instance or an integer denoting the number of seconds since epoch (1970-01-01 00:00:00). The second argument is a boolen that determines whether the scheduled execution time should be returned along with the job instances.

Example

.. code-block:: python

# get all jobs until 2012-11-30 10:00:00
list_of_job_instances = scheduler.get_jobs(until=datetime(2012, 10, 30, 10))

# get all jobs for the next hour
list_of_job_instances = scheduler.get_jobs(until=timedelta(hours=1))

# get all jobs with execution times
jobs_and_times = scheduler.get_jobs(with_times=True)
# returns a list of tuples:
# [(<rq.job.Job object at 0x123456789>, datetime.datetime(2012, 11, 25, 12, 30)), ...]

---

Checking if a job is scheduled

You can check whether a specific job instance or job id is scheduled for execution using the familiar python in operator

.. code-block:: python

if job_instance in scheduler:
    # Do something
# or
if job_id in scheduler:
    # Do something

---

Canceling a job

To cancel a job, simply pass a Job or a job id to scheduler.cancel

.. code-block:: python

scheduler.cancel(job)

Note that this method returns None whether the specified job was found or not.

---

Running the scheduler

RQ Scheduler_ comes with a script rqscheduler that runs a scheduler process that polls Redis once every minute and move scheduled jobs to the relevant queues when they need to be executed

.. code-block:: bash

# This runs a scheduler process using the default Redis connection
rqscheduler

If you want to use a different Redis server you could also do

.. code-block:: bash

rqscheduler --host localhost --port 6379 --db 0

The script accepts these arguments:

• -H or --host: Redis server to connect to
• -p or --port: port to connect to
• -d or --db: Redis db to use
• -P or --password: password to connect to Redis
• -b or --burst: runs in burst mode (enqueue scheduled jobs whose execution time is in the past and quit)
• -i INTERVAL or --interval INTERVAL: How often the scheduler checks for new jobs to add to the queue (in seconds, can be floating-point for more precision).
• -j or --job-class: specify custom job class for rq to use (python module.Class)
• -q or --queue-class: specify custom queue class for rq to use (python module.Class)

The arguments pull default values from environment variables with the same names but with a prefix of RQ_REDIS_.