Setting up the Delay Jobs gem

I am using Ruby on Rails 3.0.9 and I am trying to setup the delay_job gem for my web application in order to send emails in this way:

Notifier.delay.send_email(@user)

As well as written in the official gem documentation, to start my "delayed jobs" I should use one of the following line of code

$ 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

or invoke the rake jobs:work task.

In production mode I prefer to use one of the RAILS_ENV=... statements, but I would like to know where (that is, in which file) I should add that code in order to start the workers on application start (BTW: at this time I am not using Capistrano to deploy my application).

More, I would like to know what exactly "workers" are and if my VPS hosting (running Ubuntu 10.04 LTS) can run multiple of those or how to know how many workers my server can run.

Finally, I would like to know what options can I add in the config/initializers/delayed_job.rb file and if there are some advices or tricks about the Delay Job gem.

To start your workers on application start I would just call the proper command from an initalizer. The code to do this would look like:

system "RAILS_ENV=production #{Rails.root.join('script','delayed_job')} stop"
system "RAILS_ENV=production #{Rails.root.join('script','delayed_job')} -n 2 start"

The path might be a little off and there most likely is a cleaner way to do it but I dont know of anything off of the top of my head.