Modified DelayedJob workflow to use the Document's ID rather than serializing the entire Document object.

gistfile1.rb

class Document < ActiveRecord::Base

  # Environment-specific direct upload url verifier screens for malicious posted upload locations.
  DIRECT_UPLOAD_URL_FORMAT = %r{\Ahttps:\/\/s3\.amazonaws\.com\/myapp#{!Rails.env.production? ? "\\-#{Rails.env}" : ''}\/(?<path>uploads\/.+\/(?<filename>.+))\z}.freeze
  
  belongs_to :user
  has_attached_file :upload

  validates :direct_upload_url, presence: true, format: { with: DIRECT_UPLOAD_URL_FORMAT }
    
  before_create :set_upload_attributes
  after_create :queue_processing
  
  attr_accessible :direct_upload_url
  
  # Store an unescaped version of the escaped URL that Amazon returns from direct upload.
  def direct_upload_url=(escaped_url)
    write_attribute(:direct_upload_url, (CGI.unescape(escaped_url) rescue nil))
  end
  
  # Determines if file requires post-processing (image resizing, etc)
  def post_process_required?
    %r{^(image|(x-)?application)/(bmp|gif|jpeg|jpg|pjpeg|png|x-png)$}.match(upload_content_type).present?
  end
  
  # Final upload processing step
  def self.transfer_and_cleanup(id)
    document = Document.find(id)
    direct_upload_url_data = DIRECT_UPLOAD_URL_FORMAT.match(document.direct_upload_url)
    s3 = AWS::S3.new
    
    if document.post_process_required?
      document.upload = URI.parse(URI.escape(document.direct_upload_url))
    else
      paperclip_file_path = "documents/uploads/#{id}/original/#{direct_upload_url_data[:filename]}"
      s3.buckets[Rails.configuration.aws[:bucket]].objects[paperclip_file_path].copy_from(direct_upload_url_data[:path])
    end

    document.processed = true
    document.save
    
    s3.buckets[Rails.configuration.aws[:bucket]].objects[direct_upload_url_data[:path]].delete
  end
      
  protected
  
  # Set attachment attributes from the direct upload
  # @note Retry logic handles S3 "eventual consistency" lag.
  def set_upload_attributes
    tries ||= 5
    direct_upload_url_data = DIRECT_UPLOAD_URL_FORMAT.match(direct_upload_url)
    s3 = AWS::S3.new
    direct_upload_head = s3.buckets[Rails.configuration.aws[:bucket]].objects[direct_upload_url_data[:path]].head

    self.upload_file_name     = direct_upload_url_data[:filename]
    self.upload_file_size     = direct_upload_head.content_length
    self.upload_content_type  = direct_upload_head.content_type
    self.upload_updated_at    = direct_upload_head.last_modified
  rescue AWS::S3::Errors::NoSuchKey => e
    tries -= 1
    if tries > 0
      sleep(3)
      retry
    else
      false
    end
  end
  
  # Queue file processing
  def queue_processing
    Document.delay.transfer_and_cleanup(id)
  end

end