Delayed Job is a plugin used to execute long running jobs in background. For example, downloads, uploads, external interactions etc. And you can also specify when to start a delayed job.

To install delayed_job plugin:

script/plugin install git://github.com/tobi/delayed_job.git

After installation you need to create a table for the delayed job to save the jobs.

script/generate migration create_table_for_delayed_job

And add the following script to the migration file.

class CreateTableForDelayedJob < ActiveRecord::Migration
    def self.up
       create_table :delayed_jobs, :force => true do |t|
          t.integer :priority, :default => 0
          t.integer :attempts, :default => 0
          t.text :handler
          t.text :last_error
          t.datetime :run_at
          t.datetime :locked_at
          t.datetime :failed_at
          t.string :locked_by
          t.timestamps
       end
    end

    def self.down
       drop_table :delayed_jobs
    end
end


Now run the migration:

rake db:migrate


To add a job to delayed_job you can use the enqueue method of Delayed Job. First you have to create a Job Class, for example we need to send a notification mail using delayed job. Then we create a lib file with the content:

Class DelayedNotificationMail
   attr_accessor :id


   def initialize(id)
      self.id = id
   end


   def perform
   end
end

Now we can add job to the delayed_job using:

Delayed::Job.enqueue DelayedNotificationMail.new(@user_id), 0, 1.hour.from_now


To run the jobs in background you have to execute the rake task:


rake jobs:work


This will start a process which will run the jobs in the queue, and will run the job according to the delay specified in the job.

To clear all the jobs in queue you can use the rake task:

rake jobs:clear

For more details you can go to the GitHub