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Delated_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


  • 1.6 Renamed locked_until to locked_at. We now store when we start a given task instead of how long it will be locked by the worker. This allows us to get a reading on how long a task took to execute.
  • 1.5 Job runners can now be run in parallel. Two new database columns are needed: locked_until and locked_by. This allows us to use pessimistic locking, which enables us to run as many worker processes as we need to speed up queue processing.
  • 1.0 Initial release


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

create_table :delayed_jobs, :force => true do |table| table.integer :priority, :default => 0 table.integer :attempts, :default => 0 table.text :handler table.string :last_error table.datetime :run_at table.datetime :locked_at table.string :locked_by table.timestamps end


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.

class NewsletterJob <, :emails) def perform emails.each { |e| NewsletterMailer.deliver_text_to_email(text, e) } end end Delayed::Job.enqueue‘lorem ipsum…’, Customers.find(:all).collect(&:email))

There is also a second way to get jobs in the queue: send_later., massive_csv)

This will simply create a Delayed::PerformableMethod job in the jobs table which serializes all the parameters you pass to it. There are some special smarts for active record objects
which are stored as their text representation and loaded from the database fresh when the job is actually run later.

Running the tasks

You can invoke rake jobs:work which will start working off jobs. You can cancel the rake task by CTRL-C.

At Shopify we run the the tasks from a simple script/job_runner which is being invoked by runnit:

  #!/usr/bin/env ruby
  require File.dirname(__FILE__) + '/../config/environment'
  SLEEP = 5
  trap('TERM') { puts 'Exiting...'; $exit = true }
  trap('INT')  { puts 'Exiting...'; $exit = true }
  puts "*** Starting job worker #{Delayed::Job.worker_name}"
    loop do  
      result = nil                                 
      realtime = Benchmark.realtime do  
        result = Delayed::Job.work_off      
      count = result.sum
      break if $exit
        puts 'Waiting for more jobs...'
        status = "#{count} jobs processed at %.4f j/s, %d failed ..." % [count / realtime, result.last] status
        puts status
      break if $exit
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