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https://github.com/collectiveidea/delayed_job

Database based asynchronous priority queue system -- Extracted from Shopify
https://github.com/collectiveidea/delayed_job

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Database based asynchronous priority queue system -- Extracted from Shopify

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README 

        
**If you're viewing this at https://github.com/collectiveidea/delayed_job,

you're reading the documentation for the master branch.

[View documentation for the latest release

(4.1.12).](https://github.com/collectiveidea/delayed_job/tree/v4.1.12)**



Delayed::Job

============

[![Gem Version](https://badge.fury.io/rb/delayed_job.svg)][gem]

![CI](https://github.com/collectiveidea/delayed_job/workflows/CI/badge.svg)

[![Code Climate](https://codeclimate.com/github/collectiveidea/delayed_job.svg)][codeclimate]

[![Coverage Status](https://coveralls.io/repos/collectiveidea/delayed_job/badge.svg?branch=master)][coveralls]



[gem]: https://rubygems.org/gems/delayed_job

[codeclimate]: https://codeclimate.com/github/collectiveidea/delayed_job

[coveralls]: https://coveralls.io/r/collectiveidea/delayed_job



Delayed::Job (or DJ) encapsulates the common pattern of asynchronously executing

longer tasks in the background.



It is a direct extraction from Shopify where the job table is responsible for a

multitude of core tasks. Amongst those tasks are:



* sending massive newsletters

* image resizing

* http downloads

* updating smart collections

* updating solr, our search server, after product changes

* batch imports

* spam checks



[Follow us on Twitter][twitter] to get updates and notices about new releases.



[twitter]: https://twitter.com/delayedjob



Installation

============

delayed_job 3.0.0 only supports Rails 3.0+.



delayed_job supports multiple backends for storing the job queue. [See the wiki

for other backends](https://github.com/collectiveidea/delayed_job/wiki/Backends).



If you plan to use delayed_job with Active Record, add `delayed_job_active_record` to your `Gemfile`.



```ruby

gem 'delayed_job_active_record'

```



If you plan to use delayed_job with Mongoid, add `delayed_job_mongoid` to your `Gemfile`.



```ruby

gem 'delayed_job_mongoid'

```



Run `bundle install` to install the backend and delayed_job gems.



The Active Record backend requires a jobs table. You can create that table by

running the following command:



    rails generate delayed_job:active_record

    rake db:migrate



For Rails 4.2+, see [below](#active-job)



Development

===========

In development mode, if you are using Rails 3.1+, your application code will automatically reload every 100 jobs or when the queue finishes.

You no longer need to restart Delayed Job every time you update your code in development.



Active Job

==========

In Rails 4.2+, set the queue_adapter in config/application.rb



```ruby

config.active_job.queue_adapter = :delayed_job

```



See the [rails guide](http://guides.rubyonrails.org/active_job_basics.html#setting-the-backend) for more details.



Rails 4.x

=========

If you are using the protected_attributes gem, it must appear before delayed_job in your gemfile. If your jobs are failing with:



     ActiveRecord::StatementInvalid: PG::NotNullViolation: ERROR:  null value in column "handler" violates not-null constraint



then this is the fix you're looking for.



Upgrading from 2.x to 3.0.0 on Active Record

============================================

Delayed Job 3.0.0 introduces a new column to the delayed_jobs table.



If you're upgrading from Delayed Job 2.x, run the upgrade generator to create a migration to add the column.



    rails generate delayed_job:upgrade

    rake db:migrate



Queuing Jobs

============

Call `.delay.method(params)` on any object and it will be processed in the background.



```ruby

# without delayed_job

@user.activate!(@device)



# with delayed_job

@user.delay.activate!(@device)

```



If a method should always be run in the background, you can call

`#handle_asynchronously` after the method declaration:



```ruby

class Device

  def deliver

    # long running method

  end

  handle_asynchronously :deliver

end



device = Device.new

device.deliver

```



## Parameters



`#handle_asynchronously` and `#delay` take these parameters:



- `:priority` (number): lower numbers run first; default is 0 but can be reconfigured (see below)

- `:run_at` (Time): run the job after this time (probably in the future)

- `:queue` (string): named queue to put this job in, an alternative to priorities (see below)



These params can be Proc objects, allowing call-time evaluation of the value.



For example:



```ruby

class LongTasks

  def send_mailer

    # Some other code

  end

  handle_asynchronously :send_mailer, :priority => 20



  def in_the_future

    # Some other code

  end

  # 5.minutes.from_now will be evaluated when in_the_future is called

  handle_asynchronously :in_the_future, :run_at => Proc.new { 5.minutes.from_now }



  def self.when_to_run

    2.hours.from_now

  end



  class << self

    def call_a_class_method

      # Some other code

    end

    handle_asynchronously :call_a_class_method, :run_at => Proc.new { when_to_run }

  end



  attr_reader :how_important



  def call_an_instance_method

    # Some other code

  end

  handle_asynchronously :call_an_instance_method, :priority => Proc.new {|i| i.how_important }

end

```



If you ever want to call a `handle_asynchronously`'d method without Delayed Job, for instance while debugging something at the console, just add `_without_delay` to the method name. For instance, if your original method was `foo`, then call `foo_without_delay`.



Rails Mailers

=============

Delayed Job uses special syntax for Rails Mailers.

Do not call the `.deliver` method when using `.delay`.



```ruby

# without delayed_job

Notifier.signup(@user).deliver



# with delayed_job

Notifier.delay.signup(@user)



# delayed_job running at a specific time

Notifier.delay(run_at: 5.minutes.from_now).signup(@user)



# when using parameters, the .with method must be called before the .delay method

Notifier.with(foo: 1, bar: 2).delay.signup(@user)

```



You may also wish to consider using

[Active Job with Action Mailer](https://edgeguides.rubyonrails.org/active_job_basics.html#action-mailer)

which provides convenient `.deliver_later` syntax that forwards to Delayed Job under-the-hood.



Named Queues

============

DJ 3 introduces Resque-style named queues while still retaining DJ-style

priority. The goal is to provide a system for grouping tasks to be worked by

separate pools of workers, which may be scaled and controlled individually.



Jobs can be assigned to a queue by setting the `queue` option:



```ruby

object.delay(:queue => 'tracking').method



Delayed::Job.enqueue job, :queue => 'tracking'



handle_asynchronously :tweet_later, :queue => 'tweets'

```



You can configure default priorities for named queues:



```ruby

Delayed::Worker.queue_attributes = {

  high_priority: { priority: -10 },

  low_priority: { priority: 10 }

}

```



Configured queue priorities can be overriden by passing priority to the delay method



```ruby

object.delay(:queue => 'high_priority', priority: 0).method

```



You can start processes to only work certain queues with the `queue` and `queues`

options defined below. Processes started without specifying a queue will run jobs

from **any** queue. To effectively have a process that runs jobs where a queue is not

specified, set a default queue name with `Delayed::Worker.default_queue_name` and

have the processes run that queue.



Running Jobs

============

`script/delayed_job` can be used to manage a background process which will

start working off jobs.



To do so, add `gem "daemons"` to your `Gemfile` and make sure you've run `rails

generate delayed_job`.



You can then do the following:



    RAILS_ENV=production script/delayed_job start

    RAILS_ENV=production script/delayed_job stop



    # Runs two workers in separate processes.

    RAILS_ENV=production script/delayed_job -n 2 start

    RAILS_ENV=production script/delayed_job stop



    # Set the --queue or --queues option to work from a particular queue.

    RAILS_ENV=production script/delayed_job --queue=tracking start

    RAILS_ENV=production script/delayed_job --queues=mailers,tasks start



    # Use the --pool option to specify a worker pool. You can use this option multiple times to start different numbers of workers for different queues.

    # The following command will start 1 worker for the tracking queue,

    # 2 workers for the mailers and tasks queues, and 2 workers for any jobs:

    RAILS_ENV=production script/delayed_job --pool=tracking --pool=mailers,tasks:2 --pool=*:2 start



    # Runs all available jobs and then exits

    RAILS_ENV=production script/delayed_job start --exit-on-complete

    # or to run in the foreground

    RAILS_ENV=production script/delayed_job run --exit-on-complete



**Rails 4:** *replace script/delayed_job with bin/delayed_job*



Workers can be running on any computer, as long as they have access to the

database and their clock is in sync. Keep in mind that each worker will check

the database at least every 5 seconds.



You can also invoke `rake jobs:work` which will start working off jobs. You can

cancel the rake task with `CTRL-C`.



If you want to just run all available jobs and exit you can use `rake jobs:workoff`



Work off queues by setting the `QUEUE` or `QUEUES` environment variable.



    QUEUE=tracking rake jobs:work

    QUEUES=mailers,tasks rake jobs:work



Restarting delayed_job

======================



The following syntax will restart delayed jobs:



    RAILS_ENV=production script/delayed_job restart



To restart multiple delayed_job workers:



    RAILS_ENV=production script/delayed_job -n2 restart



**Rails 4:** *replace script/delayed_job with bin/delayed_job*



Custom Jobs

===========

Jobs are simple ruby objects with a method called perform. Any object which responds to perform can be stuffed into the jobs table. Job objects are serialized to yaml so that they can later be resurrected by the job runner.



```ruby

NewsletterJob = Struct.new(:text, :emails) do

  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end

end



Delayed::Job.enqueue NewsletterJob.new('lorem ipsum...', Customers.pluck(:email))

```



To set a per-job max attempts that overrides the Delayed::Worker.max_attempts you can define a max_attempts method on the job



```ruby

NewsletterJob = Struct.new(:text, :emails) do

  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end



  def max_attempts

    3

  end

end

```



To set a per-job max run time that overrides the Delayed::Worker.max_run_time you can define a max_run_time method on the job



NOTE: this can ONLY be used to set a max_run_time that is lower than Delayed::Worker.max_run_time. Otherwise the lock on the job would expire and another worker would start the working on the in progress job.



```ruby

NewsletterJob = Struct.new(:text, :emails) do

  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end



  def max_run_time

    120 # seconds

  end

end

```



To set a per-job default for destroying failed jobs that overrides the Delayed::Worker.destroy_failed_jobs you can define a destroy_failed_jobs? method on the job



```ruby

NewsletterJob = Struct.new(:text, :emails) do

  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end



  def destroy_failed_jobs?

    false

  end

end

```



To set a default queue name for a custom job that overrides Delayed::Worker.default_queue_name, you can define a queue_name method on the job



```ruby

NewsletterJob = Struct.new(:text, :emails) do

  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end



  def queue_name

    'newsletter_queue'

  end

end

```



On error, the job is scheduled again in 5 seconds + N ** 4, where N is the number of attempts. You can define your own `reschedule_at` method to override this default behavior.



```ruby

NewsletterJob = Struct.new(:text, :emails) do

  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end



  def reschedule_at(current_time, attempts)

    current_time + 5.seconds

  end

end

```



Hooks

=====

You can define hooks on your job that will be called at different stages in the process:



**NOTE:** If you are using ActiveJob these hooks are **not** available to your jobs. You will need to use ActiveJob's callbacks. You can find details here https://guides.rubyonrails.org/active_job_basics.html#callbacks



```ruby

class ParanoidNewsletterJob < NewsletterJob

  def enqueue(job)

    record_stat 'newsletter_job/enqueue'

  end



  def perform

    emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) }

  end



  def before(job)

    record_stat 'newsletter_job/start'

  end



  def after(job)

    record_stat 'newsletter_job/after'

  end



  def success(job)

    record_stat 'newsletter_job/success'

  end



  def error(job, exception)

    Airbrake.notify(exception)

  end



  def failure(job)

    page_sysadmin_in_the_middle_of_the_night

  end

end

```



Gory Details

============

The library revolves around a delayed_jobs table which looks as follows:



```ruby

create_table :delayed_jobs, :force => true do |table|

  table.integer  :priority, :default => 0      # Allows some jobs to jump to the front of the queue

  table.integer  :attempts, :default => 0      # Provides for retries, but still fail eventually.

  table.text     :handler                      # YAML-encoded string of the object that will do work

  table.text     :last_error                   # reason for last failure (See Note below)

  table.datetime :run_at                       # When to run. Could be Time.zone.now for immediately, or sometime in the future.

  table.datetime :locked_at                    # Set when a client is working on this object

  table.datetime :failed_at                    # Set when all retries have failed (actually, by default, the record is deleted instead)

  table.string   :locked_by                    # Who is working on this object (if locked)

  table.string   :queue                        # The name of the queue this job is in

  table.timestamps

end

```



On error, the job is scheduled again in 5 seconds + N ** 4, where N is the number of attempts or using the job's defined `reschedule_at` method.



The default `Worker.max_attempts` is 25. After this, the job is either deleted (default), or left in the database with "failed_at" set.

With the default of 25 attempts, the last retry will be 20 days later, with the last interval being almost 100 hours.



The default `Worker.max_run_time` is 4.hours. If your job takes longer than that, another computer could pick it up. It's up to you to

make sure your job doesn't exceed this time. You should set this to the longest time you think the job could take.



By default, it will delete failed jobs (and it always deletes successful jobs). If you want to keep failed jobs, set

`Delayed::Worker.destroy_failed_jobs = false`. The failed jobs will be marked with non-null failed_at.



By default all jobs are scheduled with `priority = 0`, which is top priority. You can change this by setting `Delayed::Worker.default_priority` to something else. Lower numbers have higher priority.



The default behavior is to read 5 jobs from the queue when finding an available job. You can configure this by setting `Delayed::Worker.read_ahead`.



By default all jobs will be queued without a named queue. A default named queue can be specified by using `Delayed::Worker.default_queue_name`.



If no jobs are found, the worker sleeps for the amount of time specified by the sleep delay option. Set `Delayed::Worker.sleep_delay = 60` for a 60 second sleep time.



It is possible to disable delayed jobs for testing purposes. Set `Delayed::Worker.delay_jobs = false` to execute all jobs realtime.



Or `Delayed::Worker.delay_jobs` can be a Proc that decides whether to execute jobs inline on a per-job basis:



```ruby

Delayed::Worker.delay_jobs = ->(job) {

  job.queue != 'inline'

}

```



You may need to raise exceptions on SIGTERM signals, `Delayed::Worker.raise_signal_exceptions = :term` will cause the worker to raise a `SignalException` causing the running job to abort and be unlocked, which makes the job available to other workers. The default for this option is false.



Here is an example of changing job parameters in Rails:



```ruby

# config/initializers/delayed_job_config.rb

Delayed::Worker.destroy_failed_jobs = false

Delayed::Worker.sleep_delay = 60

Delayed::Worker.max_attempts = 3

Delayed::Worker.max_run_time = 5.minutes

Delayed::Worker.read_ahead = 10

Delayed::Worker.default_queue_name = 'default'

Delayed::Worker.delay_jobs = !Rails.env.test?

Delayed::Worker.raise_signal_exceptions = :term

Delayed::Worker.logger = Logger.new(File.join(Rails.root, 'log', 'delayed_job.log'))

```



Cleaning up

===========

You can invoke `rake jobs:clear` to delete all jobs in the queue.



Having problems?

================

Good places to get help are:

* [Google Groups](http://groups.google.com/group/delayed_job) where you can join our mailing list.

* [StackOverflow](http://stackoverflow.com/questions/tagged/delayed-job)