This is a comprehensive XML generation benchmark with some of the most popular Ruby gems

benchmark_xml_render.rb

# gem install benchmark-memory activesupport builder nokogiri rabl ox libxml-ruby

require 'benchmark'
require 'benchmark-memory'
require 'builder'
require 'active_support/core_ext/hash/conversions'
require 'rabl'
require 'nokogiri'
require 'libxml'
require 'ox'

class BaseModel
  def initialize(attrs={})
    attrs.each { |k, v| self.send("#{k}=", v) }
  end
end
class UserModel < BaseModel
  attr_accessor :name, :age, :email
end
class CommentModel < BaseModel
  attr_accessor :user, :message, :created_at, :attachment
end
class PostModel < BaseModel
  attr_accessor :content, :author, :comments, :created_at, :published
end

def create_post(size=1_000, comments=10, attachment_size=0)
  PostModel.new(
    content: '-'*size,
    author: UserModel.new(name: 'First Last', age: rand(100), email: 'user@email.com'),
    created_at: Time.now,
    published: true,
    comments: comments.times.map do
      CommentModel.new(
        user: UserModel.new(name: 'First Last', age: rand(100), email: 'user@email.com'),
        message: '-'*400,
        created_at: Time.now,
        attachment: '-'*attachment_size
      )
    end
  )
end

post1 = create_post(1_000, 10, 0)
post2 = create_post(1_000_000, 200, 1_000)
post3 = create_post(10_000_000, 5_000, 10_000)

# uses Builder
# https://github.com/rails/rails/blob/5-2-stable/activesupport/lib/active_support/core_ext/hash/conversions.rb#L75-L92
def render_toxml(post)
  {
    'content'     => post.content,
    'created_at'  => post.created_at,
    'published'   => post.published,

    'author'      => {
      'name'  => post.author.name,
      'age'   => post.author.age,
      'email' => post.author.email,
    },

    'comments'    => post.comments.map do |comment|
      {
        'created_at' => comment.created_at,
        'message'    => comment.message,
        'user'       => {
          'name'  => comment.user.name,
          'age'   => comment.user.age,
          'email' => comment.user.email,
        },
        'attachment' => comment.attachment,
      }
    end
  }.to_xml(root: 'post')
end

def render_stringc(post) # more concatenation
  xml = '<?xml version="1.0" encoding="UTF-8"?>'
  xml << '<post>'
  xml << "  <content>#{post.content.encode(xml: :text)}</content>"
  xml << "  <created-at type=\"dateTime\">#{post.created_at.iso8601}</created-at>"
  xml << "  <published type=\"boolean\">#{post.published}</published>"
  xml << '  <author>'
  xml << "    <name>#{post.author.name.encode(xml: :text)}</name>"
  xml << "    <age type=\"integer\">#{post.author.age}</age>"
  xml << "    <email>#{post.author.email.encode(xml: :text)}</email>"
  xml << '  </author>'
  xml << '  <comments type="array">'
  post.comments.each do |comment|
    xml << '  <comment>'
    xml << "    <created-at type=\"dateTime\">#{comment.created_at.iso8601}</created-at>"
    xml << "    <message>#{comment.message.encode(xml: :text)}</message>"
    xml << '    <user>'
    xml << "      <name>#{comment.user.name.encode(xml: :text)}</name>"
    xml << "      <age type=\"integer\">#{comment.user.age}</age>"
    xml << "      <email>#{comment.user.email.encode(xml: :text)}</email>"
    xml << '    </user>'
    xml << "    <attachment>#{comment.attachment.encode(xml: :text)}</attachment>"
    xml << '  </comment>'
  end
  xml << '  </comments>'
  xml << '</post>'
  xml
end

def render_stringi(post) # only interpolation
  %(<?xml version="1.0" encoding="UTF-8"?>
<post>
  <content>#{post.content.encode(xml: :text)}</content>
  <created-at type="dateTime">#{post.created_at.iso8601}</created-at>
  <published type="boolean">#{post.published}</published>
  <author>
    <name>#{post.author.name.encode(xml: :text)}</name>
    <age type="integer">#{post.author.age}</age>
    <email>#{post.author.email.encode(xml: :text)}</email>
  </author>
  <comments type="array">
  #{
    post.comments.map do |comment|
      %(
      <comment>
        <created-at type="dateTime">#{comment.created_at.iso8601}</created-at>
        <message>#{comment.message.encode(xml: :text)}</message>
        <user>
          <name>#{comment.user.name.encode(xml: :text)}</name>
          <age type="integer">#{comment.user.age}</age>
          <email>#{comment.user.email.encode(xml: :text)}</email>
        </user>
        <attachment>#{comment.attachment.encode(xml: :text)}</attachment>
      </comment>
)
    end.join('')
  }
  </comments>
</post>)
end

def render_rabl(post)
  # # Create a post.rabl file with the following content
  # attribute :content
  # attribute :created_at
  # attribute :published

  # child(:author) do
  #   attribute :name
  #   attribute :age
  #   attribute :email
  # end

  # child(:comments) do
  #   attribute :created_at
  #   attribute :message
  #   child(:user) do
  #     attribute :name
  #     attribute :age
  #     attribute :email
  #   end
  #   attribute :attachment
  # end
  Rabl.render(post, 'post', view_path: '.', format: :xml, root: 'post')
end

def render_builder(post)
  xml = Builder::XmlMarkup.new
  xml.instruct! :xml, version: '1.0', encoding: 'UTF-8'
  xml.post do |builder|
    builder.content post.content
    builder.created_at post.created_at, type: 'dateTime'
    builder.published post.published, type: 'boolean'
    builder.author do |builder|
      builder.name post.author.name
      builder.age post.author.age, type: 'integer'
      builder.email post.author.email
    end
    post.comments.each do |comment|
      builder.comments do |builder|
        builder.created_at comment.created_at, type: 'dateTime'
        builder.message comment.message
        builder.user do |builder|
          builder.name comment.user.name
          builder.age comment.user.age, type: 'integer'
          builder.email comment.user.email
        end
        builder.attachment comment.attachment
      end
    end
  end
end

def render_nokogiri(post)
  Nokogiri::XML::Builder.new do |xml|
    xml.post do
      xml.content post.content
      xml.created_at post.created_at, type: 'dateTime'
      xml.published post.published, type: 'boolean'
      xml.author do
        xml.name post.author.name
        xml.age post.author.age, type: 'integer'
        xml.email post.author.email
      end
      post.comments.each do |comment|
        xml.comments do
          xml.created_at comment.created_at, type: 'dateTime'
          xml.message comment.message
          xml.user do
            xml.name comment.user.name
            xml.age comment.user.age, type: 'integer'
            xml.email comment.user.email
          end
          xml.attachment comment.attachment
        end
      end
    end
  end.to_xml
end

def render_libxml(post)
  doc = LibXML::XML::Document.new
  doc.encoding = LibXML::XML::Encoding::UTF_8
  doc.root = root = LibXML::XML::Node.new('post')

  node = LibXML::XML::Node.new('content')
  node.content = post.content
  root << node

  node = LibXML::XML::Node.new('created-at')
  node.content = post.created_at.iso8601
  LibXML::XML::Attr.new(node, 'type', 'dateTime')
  root << node

  node = LibXML::XML::Node.new('published')
  node.content = post.published.to_s
  LibXML::XML::Attr.new(node, 'type', 'boolean')
  root << node

  author = LibXML::XML::Node.new('author')

  node = LibXML::XML::Node.new('name')
  node.content = post.author.name
  author << node

  node = LibXML::XML::Node.new('age')
  node.content = post.author.age.to_s
  LibXML::XML::Attr.new(node, 'type', 'integer')
  author << node

  node = LibXML::XML::Node.new('email')
  node.content = post.author.email
  author << node

  root << author

  comments = LibXML::XML::Node.new('comments')
  LibXML::XML::Attr.new(comments, 'type', 'array')
  post.comments.each do |comment|
    node_comment = LibXML::XML::Node.new('comment')

    node = LibXML::XML::Node.new('created-at')
    node.content = comment.created_at.iso8601
    LibXML::XML::Attr.new(node, 'type', 'dateTime')
    node_comment << node

    node = LibXML::XML::Node.new('message')
    node.content = comment.message
    node_comment << node

    user = LibXML::XML::Node.new('user')

    node = LibXML::XML::Node.new('name')
    node.content = comment.user.name
    user << node

    node = LibXML::XML::Node.new('age')
    node.content = comment.user.age.to_s
    LibXML::XML::Attr.new(node, 'type', 'integer')
    user << node

    node = LibXML::XML::Node.new('email')
    node.content = comment.user.email
    user << node

    node_comment << user

    node = LibXML::XML::Node.new('attachment')
    node.content = comment.attachment
    node_comment << node

    comments << node_comment
  end

  root << comments

  doc.to_s
end

def render_ox(post)
  doc = Ox::Document.new(:version => '1.0')

  instruct = Ox::Instruct.new(:xml)
  instruct[:version] = '1.0'
  instruct[:encoding] = 'UTF-8'
  doc << instruct

  root = Ox::Element.new('post')
  doc << root

  node = Ox::Element.new('content')
  node << post.content
  root << node

  node = Ox::Element.new('created-at')
  node[:type] = 'dateTime'
  node << post.created_at.iso8601
  root << node

  node = Ox::Element.new('published')
  node[:type] = 'boolean'
  node << post.published.to_s
  root << node

  author = Ox::Element.new('author')

  node = Ox::Element.new('name')
  node << post.author.name
  author << node

  node = Ox::Element.new('age')
  node[:type] = 'integer'
  node << post.author.age.to_s
  author << node

  node = Ox::Element.new('email')
  node << post.author.email
  author << node

  root << author

  comments = Ox::Element.new('comments')
  comments[:type] = 'array'
  post.comments.each do |comment|
    node_comment = Ox::Element.new('comment')

    node = Ox::Element.new('created-at')
    node[:type] = 'dateTime'
    node << comment.created_at.iso8601
    node_comment << node

    node = Ox::Element.new('message')
    node << comment.message
    node_comment << node

    user = Ox::Element.new('user')

    node = Ox::Element.new('name')
    node << comment.user.name
    user << node

    node = Ox::Element.new('age')
    node[:type] = 'integer'
    node << comment.user.age.to_s
    user << node

    node = Ox::Element.new('email')
    node << comment.user.email
    user << node

    node_comment << user

    node = Ox::Element.new('attachment')
    node << comment.attachment
    node_comment << node

    comments << node_comment
  end

  root << comments

  Ox.dump(doc)
end

# Confirm rendering is working fine
puts "Are the renderers consistent?"
puts ([render_stringc(post1), render_stringi(post1), render_toxml(post1),
render_builder(post1), render_rabl(post1), render_nokogiri(post1),
render_libxml(post1), render_ox(post1)].map { |xml| Hash.from_xml(xml) }.uniq.size == 1)


[post1, post2, post3].each_with_index do |post_i, i|
  puts
  puts '------------------'
  puts "Benchmark of post#{i+1}"
  puts '------------------'

  nrep = 1000
  bench = Benchmark.bm(10) do |x|
    x.report('toxml:')  { nrep.times { render_toxml(post_i) } }
    x.report('stringc:')  { nrep.times { render_stringc(post_i) } }
    x.report('stringi:')  { nrep.times { render_stringi(post_i) } }
    x.report('rabl:')  { nrep.times { render_rabl(post_i) } }
    x.report('builder:')  { nrep.times { render_builder(post_i) } }
    x.report('nokogiri:')  { nrep.times { render_nokogiri(post_i) } }
    x.report('libxml:')  { nrep.times { render_libxml(post_i) } }
    x.report('ox:')  { nrep.times { render_ox(post_i) } }
  end

  puts
  puts "Results in ms per execution:"
  bench.each do |bm|
    puts ">>>>> #{bm.label} - %.3f ms" % (bm.real*1000.0/nrep)
  end
  puts

  Benchmark.memory do |x|
    x.report('toxml:')  { render_toxml(post_i) }
    x.report('stringc:')  { render_stringc(post_i) }
    x.report('stringi:')  { render_stringi(post_i) }
    x.report('rabl:')  { render_rabl(post_i) }
    x.report('builder:')  { render_builder(post_i) }
    x.report('nokogiri:')  { render_nokogiri(post_i) }
    x.report('libxml:')  { render_libxml(post_i) }
    x.report('ox:')  { render_ox(post_i) }
    x.compare!
  end
end