active_job / delayed_job を高速化するハック ref: https://qiita.com/tonluqclml/items/f6a0411a8fbe3031cb0d

file0.rb

class CsvFormController < ApplicationController
  # 「名前・年齢・メールアドレス」のCSVファイルをアップロードして、Userを作れる画面
  #
  #   太郎,32,taro@example.com
  #   二郎,30,jiro@example.com
  #   三郎,27,sabu@example.com
  def upload
    rows = CSV.parse(params[:file].read)
    UserUploadJob.perform_later(rows: rows)
  end
end

class UserUploadJob < ApplicationJob
  def perform(rows:)
    User.transaction do
      rows.each do |row|
        User.create!(name: row[0], age: row[1], email: row[2])
      end
    end
    # 処理が終わったら、メールやSlackで通知
  end
end

file1.rb

module Delayed
  module Backend
    module Base
      ...

      def payload_object=(object)
        @payload_object = object
        self.handler = object.to_yaml
      end

      ...
    end
  end
end

file2.rb

require 'benchmark'
require 'json'
require 'yaml'

large_array = (1..1_000_000).map { |x| [x, x, x] }

puts '.to_json'
puts Benchmark::CAPTION
puts Benchmark.measure { large_array.to_json }
puts
puts '.to_yaml'
puts Benchmark::CAPTION
puts Benchmark.measure { large_array.to_yaml }

file3.txt

.to_json
      user     system      total        real
  0.180000   0.030000   0.210000 (  0.218959)

.to_yaml
      user     system      total        real
 30.350000   0.890000  31.240000 ( 33.154655)

file4.rb

class UserUploadJob
  def serialize_arguments(args)
    params = args.first.clone

    # rows（配列の配列）を、TSV形式の文字列に変換
    params[:rows] = params[:rows].map { |r| r.join("\t") }.join("\n")
    super([params])
  end

  def deserialize_arguments(serialized_arguments)
    args = super(serialized_arguments)

    # TSV形式の文字列を配列の配列に変換
    args.first[:entries] = args.first[:entries].lines.map { |l| l.strip.split("\t") }
    args
  end