https://github.com/rails/rails/pull/36352

benchmark_pluck_datetime.rb

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails"
  gem "mysql2"
  gem "pg"
  gem "benchmark-ips"
end

require "active_record"

ActiveRecord::Base.establish_connection(adapter: "mysql2", database: "test", username: "root")
# ActiveRecord::Base.establish_connection(adapter: "postgresql", database: "test")

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :name
    t.timestamps null: false
  end
end

class User < ActiveRecord::Base
end

10.times do |i|
  User.create!(name: "user #{i}")
end

users = User.all

Benchmark.ips do |x|
  x.report("users.pluck(:id)") { users.pluck(:id) }
  x.report("users.pluck(:name)") { users.pluck(:name) }
  x.report("users.pluck(:created_at)") { users.pluck(:created_at) }
end