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FAQ

Q: How do I set the priority of a job?

A: Jobs with a higher priority number will be run before other jobs. Normally, jobs are given a priority of 0. Here’s an example where we set the priority to “1”, which means it will run before any other jobs in the queue with a lower priority number:

Delayed::Job.enqueue(NewsletterJob.new('text', User.find(:all).collect(&:email)), 1)

Q: How do I set a job to start at a later (or specific time)?

A: Here’s an example that would set the job to run 5 minutes from now. The “0” is the default priority level for the job, the “5.minutes.from_now” sets the job to run 5 minutes from the time it’s saved in the delayed_jobs table:

Delayed::Job.enqueue(NewsletterJob.new('text', User.find(:all).collect(&:email)), 0, 5.minutes.from_now)

Q: Hello, tobi, I tried this plugin but I got 2 failing built-in specs. The “delayed_job / lib / delayed / job.rb” line 94 is “(`locked_at` IS NULL OR `locked_at` < #{quote_value(now + max_run_time)})”. Should it be “(… < #{quote_value(now – max_run_time)})”?

A: I got that same error. I think it’s a problem with postgres compatibility. It appears to be fixed with this commit. This is now fixed in master; dj should support all database adapters that ActiveRecord implements.

Q: How to a configure the plugin to save failed jobs?

A: Here’s how I configured the plugin. I also wanted to change the number of max attempts, etc:

  # config/initializers/delayed_job_config.rb

  Delayed::Job.destroy_failed_jobs = false
  silence_warnings do
    Delayed::Job.const_set("MAX_ATTEMPTS", 3)
    Delayed::Job.const_set("MAX_RUN_TIME", 5.minutes)
  end

Q: I’m having trouble keeping the job running going when jobs fail. Isn’t there a way to store the error message and move on?

A: My errors are long, so I had to change the last_error column from string to text:


class ChangeLastErrorInDelayedJobsToText < ActiveRecord::Migration
  def self.up
    change_column :delayed_jobs, :last_error, :text
  end

  def self.down
    change_column :delayed_jobs, :last_error, :string
  end
end

Q: Why do I get an error talking about Struct::Group if I use Group.find within a perform method?

A: There’s a strange edge-case with Ruby/Rails where Struct::Group already exists, so calling Group.anything from within a class that inherits from Struct will have strange results. You can workaround this issue by prefixing calls to Group with two colons. For example, ::Group.find would work as expected.

Q: Why am I getting a NoMethodError error that looks like this:

NoMethodError (undefined method `second' for #<Array:0x5588d10>):
    /vendor/plugins/delayed_job/lib/delayed/job.rb:87:in `enqueue'

A: The plugin is incompatible with Rails versions less than 2.2 since this commit in delayed_job, which relies on this commit in Rails. You can upgrade to Rails 2.2, or add a core extension to Array yourself like so:

# config/environment.rb
require 'lib/core_ext'

# lib/core_ext.rb
class Array
  def from(position)
    self[position..-1]
  end

  def to(position)
    self[0..position]
  end

  def second
    self[1]
  end

  def third
    self[2]
  end
end

Q: What can I do to prevent duplicate jobs from being queued up? Shouldn’t there be a check to see if the handler is the same for a job?

Q: Is DJ designed to work exclusively with rails?

A: Not necessarily. There is an example app with Sinatra. It is dependent on ActiveRecord, however.

Q: I’m currently using a daemon to run a task every 30 seconds. Is DJ a good replacement for this?

Q: Can you provide an example of how to run the workers on a separate machine? I assume it should be the same rails project just deployed to a different machine, but maybe with a different environment so it connects to a remote server?

Q: Does each worker process run it’s own rails instance? Can you configure how often it polls the database?

Q: Can you show an example of how to save a job’s progress, so that it can resume from a failure in the middle and not duplicate work (I’m thinking for a newsletter here)?

Q. I sent a task to delayed job and it doesn’t seem to be working. How can I tell if it’s still in progress or whether there was an error that stopped it?

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