Avoid DB and Queue race

example.rb

class User < ActiveRecord::Base
  after_save :queue_welcome_email, :on => :create

  private
  def queue_welcome_email
    Resque.enqueue(WelcomeEmailJob, Marshal.
      dump({ :email => self.email, :full_name => "#{self.first_name} #{self.last_name}" }))
  end
end

class WelcomeEmailJob
  @queue = :normal

  def self.perform(user_data)
    UserMailer.welcome_email(Marshal.load(user_data)).deliver
  end
end