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Hello!

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doES iT sCaLe?

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Jubilee Year

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Look at all the things I’m NOT doing!

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Prologue

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Ruby Script

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But At What Cost?

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Aaron Patterson

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Live From Here

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I have stickers of my cat! (please say "hello")

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@tenderlove

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Other == Puns?

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Speaking of Twitter…

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@buritica

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~54% useless

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March 14, 2019

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"But At What Cost?" Bot

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Twitter: 100% Useless

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Facepalm-er

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Facepalm-ee

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Response Algorithm Is it a pun? "Aaron" "But At What Cost?" Yes No

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Let’s Practice

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G GitHub

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Active Job

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G GitHub We’re Hiring!!!!

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http://git.io/sparkles

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Ruby Core Team

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10 Years On Ruby Core! W ow !!!

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Rails Core Team

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I ❤ Ruby

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Just Worked™

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No Boilerplate

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Java (1.3?) vs Ruby List list = new ArrayList(); list.add("1"); list.add("2"); list.add("3"); Iterator iter = list.iterator(); List intList = new ArrayList(); while (iter.hasNext()) { String str = (String)iter.next(); intList.add(Integer.parseInt(str)); } list = %w{ 1 2 3 } intList = list.map { |l| l.to_i } Java Ruby

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My First Ruby Program Serious ^

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Never Write Inﬁnite Loops

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I ❤ Rails

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No content

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Just Worked™

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No Boilerplate

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Community Values

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"I MUST WRITE RAILS!"

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BUT AT WHAT COST?

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-25% $114k ➡ $85k (in 2006)

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More Companies

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More People

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Thank You!

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#ENDGAME

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BUT AT WHAT COST?

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No content

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Game of Thrones

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Dumbledore Dies

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Cool Performance Tips

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No Parenthesis is Faster

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Parens vs No Parens def foo1(bar, baz) end def foo2(bar, baz) end def foo3(bar, baz) end def foo1 bar, baz end def foo2 bar, baz end def foo3 bar, baz end Parens No Parens

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"No code is faster than no code"

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ruby -y

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Parse States $ ruby --disable-gems -y with-parens.rb | wc -l 805 $ ruby --disable-gems -y without-parens.rb | wc -l 778

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Single Quotes Are 2x Faster Than Double Quotes

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You Have To Hit The Shift Key To Type "

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Actual Performance Tip Rails 6!

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Allocation Count Started GET "/users/new" for ::1 at 2019-04-30 16:45:49 -0500 Processing by UsersController#new as */* Rendering users/new.html.erb within layouts/application Rendered users/_form.html.erb (Duration: 1.4ms | Allocations: 552) Rendered users/new.html.erb within layouts/application (Duration: 1.7ms | Allocations: 640) Completed 200 OK in 6ms (Views: 5.4ms | ActiveRecord: 0.0ms | Allocations: 4140) Started GET "/users/new" for ::1 at 2019-04-30 16:47:02 -0500 Processing by UsersController#new as */* Rendering users/new.html.erb within layouts/application Rendered users/_form.html.erb (Duration: 1.4ms | Allocations: 827) Rendered users/_expensive.html.erb (Duration: 1.6ms | Allocations: 10098) Rendered users/new.html.erb within layouts/application (Duration: 4.3ms | Allocations: 11553) Completed 200 OK in 9ms (Views: 8.5ms | ActiveRecord: 0.0ms | Allocations: 15981)

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Rails at GitHub

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Template Pre-Compilation Method Name Generation

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Template Pre- Compilation

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Method Name Generation

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Build a Template Renderer!

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Rails is MVC

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MVC Model View Controller Request

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Modal View Controller

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MVC Model View Controller Request Action Controller Action View Active Record

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Action View

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Action View Finds Templates Compiles Templates Executes Views

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View Templates

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ERB

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Developed by @m_seki

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ERB Template

New User

<%= render_form %> <%= link_to 'Back' %> new.html.erb

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ERB Compiler require "erb" # Compile the template template = ERB.new File.read "test.html.erb" # Print the template source puts template.src # Evaluate the template puts template.result(binding) compile.rb

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Compiled Template _erbout = +"" _erbout << "

New User

\n\n".freeze _erbout << render_form.to_s _erbout << "\n\n".freeze _erbout << link_to("Back").to_s _erbout << "\n".freeze _erbout

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Modiﬁed Compile Script require "erb" def render_form "" end def link_to(text) "#{text}" end # Compile the template template = ERB.new File.read "test.html.erb" # Evaluate the template puts template.result(binding)

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Compiler Output $ ruby compiler.rb

New User

Back

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ERB Translations ERB Source Translated Ruby <%= something %> _erbout << something.to_s <% something_else %> something_else

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Capturing Blocks

<%= capture do %> Hello! <% end %>

require "erb" def capture yield end # Compile the template template = ERB.new File.read "test.html.erb" puts template.result(binding)

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What is the output? Hello!

Hello!

ERROR!

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Compiled Source _erbout = +'' _erbout << "

\n ".freeze _erbout << ( capture do ).to_s _erbout << "\n Hello!\n ".freeze end _erbout << "\n

\n".freeze _erbout

<%= capture do %> Hello! <% end %>

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Compiled Source _erbout = +'' _erbout << "

\n ".freeze _erbout << ( capture do ).to_s _erbout << "\n Hello!\n ".freeze end _erbout << "\n

\n".freeze _erbout

<%= capture do %> Hello! <% end %>

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How does this work in Rails?

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ERB Compiler BLOCK_EXPR = /\s*((\s+|\))do|\{)(\s*\|[^|]*\|)?\s*\Z/ def add_expression(indicator, code) flush_newline_if_pending(src) if (indicator == "==") || @escape src << "@output_buffer.safe_expr_append=" else src << "@output_buffer.append=" end if BLOCK_EXPR.match?(code) src << " " << code else src << "(" << code << ");" end end

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ERB in Rails

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Different ERB Flavors Original ERB ERubis ERubi

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ERB Performance

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Rendering Speed require "erb" require "benchmark/ips" class AaronView TEMPLATES = { } TEMPLATES["index"] = <<-eerb

Hello <%= name %>

eerb def name; "Aaron"; end def render(template) ERB.new(TEMPLATES[template]).result(binding) end end view = AaronView.new Benchmark.ips do |x| x.report("render") { view.render("index") } end

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Rendering Speed $ ruby rendering_speed.rb Warming up -------------------------------------- render 2.696k i/100ms Calculating ------------------------------------- render 27.117k (± 5.9%) i/s - 137.496k in 5.092633s

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Cache Compilation class AaronView TEMPLATES = { } TEMPLATES["index"] = <<-eerb

Hello <%= name %>

eerb def name; "Aaron"; end def render(template) ERB.new(TEMPLATES[template]).result(binding) end COMPILED_TEMPLATES = { } def render_compiled(template) erb = COMPILED_TEMPLATES[template] ||= ERB.new(TEMPLATES[template]) erb.result(binding) end end view = AaronView.new Benchmark.ips do |x| x.report("render") { view.render("index") } x.report("render compiled") { view.render_compiled("index") } x.compare! end

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Cache Compilation $ ruby rendering_speed.rb Warming up -------------------------------------- render 2.709k i/100ms render compiled 6.293k i/100ms Calculating ------------------------------------- render 27.115k (± 2.6%) i/s - 138.159k in 5.098881s render compiled 63.645k (± 3.9%) i/s - 320.943k in 5.050544s Comparison: render compiled: 63645.5 i/s render: 27114.8 i/s - 2.35x slower

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Deﬁne a Method class AaronView TEMPLATES = { } TEMPLATES["index"] = <<-eerb

Hello <%= name %>

eerb def name; "Aaron"; end def render(template) ERB.new(TEMPLATES[template]).result(binding) end COMPILED_TEMPLATES = { } def render_compiled(template) erb = COMPILED_TEMPLATES[template] ||= ERB.new(TEMPLATES[template]) erb.result(binding) end METHODS_DEFINED = { } def render_with_method(template) unless METHODS_DEFINED.key? template erb = ERB.new(TEMPLATES[template]) self.class.class_eval "def render_#{template}; #{erb.src}; end" METHODS_DEFINED[template] = true end send "render_#{template}" end end

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Deﬁne a Method $ ruby rendering_speed.rb Warming up -------------------------------------- render 2.750k i/100ms render compiled 6.462k i/100ms render method 114.420k i/100ms Calculating ------------------------------------- render 28.389k (± 2.7%) i/s - 143.000k in 5.041158s render compiled 65.860k (± 2.4%) i/s - 329.562k in 5.006962s render method 1.477M (± 1.7%) i/s - 7.437M in 5.038304s Comparison: render method: 1476591.3 i/s render compiled: 65860.1 i/s - 22.42x slower render: 28388.6 i/s - 52.01x slower

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Method Generation require "erb" erb_source = <<-erb

Hello <%= name %>

erb erb = ERB.new erb_source template = "index" self.class.class_eval "def render_#{template}; #{erb.src}; end" send "render_#{template}" Template Source Compile Source Deﬁne a m ethod Render the Template

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Method Generation def render_index _erbout = +'' _erbout << "\n \n

Hello ".freeze _erbout << name.to_s _erbout << "

\n\n".freeze _erbout end Compiled Source

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Templates Are Translated to Methods

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Rails Template Methods

This is an inner template <% puts methods.grep(/_app/) %>

Template in Rails

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Rails Template Methods Console Output _app_views_users_index_html_erb___4485674087862414886_70282093274980 _app_views_users__first_ja_html_erb__657974686689484881_70282053324000 _app_views_users__second_html_erb___3508242123539422948_70282053523460

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Memory Size def render_index _erbout = +'' _erbout << "\n \n

Hello ".freeze _erbout << name.to_s _erbout << "

\n\n".freeze _erbout end require "objspace" iseq = RubyVM::InstructionSequence.of( method(:render_index)) p ObjectSpace.memsize_of iseq $ ruby test.rb 1264

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Template Handling In Rails

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Instance Variable Visibility

This is template Foo!

<%= @some_ivar %>

This is template Bar!

<%= @some_ivar %> _foo.html.erb _bar.html.erb

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Compiled Templates class ActionView::Base def render_foo _erbout = +'' _erbout << "

This is template Foo!

\n".freeze _erbout << @some_ivar.to_s _erbout << "\n".freeze _erbout end def render_bar _erbout = +'' _erbout << "

This is template Barr!

\n".freeze _erbout << @some_ivar.to_s _erbout << "\n".freeze _erbout end end _foo.html.erb _bar.html.erb Same Instance Same Instance

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Don’t use instance variables in your templates

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"Don’t use instance variables in your templates" - Aaron

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Instance Variable Visibility

This is template Foo!

<%= @some_ivar %>

This is template Bar!

<%= @some_ivar %> _foo.html.erb _bar.html.erb

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Local Variables

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Rendering With Locals <%= render "content", locals: { name: "Gorby" } %>

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Compiling With Locals

Hello, <%= name %>

def render_content _erbout = +'' _erbout << "

\n Hello, ".freeze _erbout << name.to_s _erbout << "\n

\n".freeze _erbout end content.html.erb Compiled Method Method Call

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Preamble With Locals

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Compiling With Locals

Hello, <%= name %>

def render_content(locals) # Locals preamble name = locals[:name] _erbout = +'' _erbout << "

\n Hello, ".freeze _erbout << name.to_s _erbout << "\n

\n".freeze _erbout end content.html.erb Compiled Method

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Templates Require Context <%= render "content", locals: { name: "Gorby" } %> <%= render "content" %>

Hello, <%= name %>

main.html.erb content.html.erb Method call or local variable? local variable method call

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Templates Can’t Be Compiled In Advance* *(FORESHADOWING)

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Compiled Too Many Times

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Too Many Compilations <%= render "content", locals: { name: "Gorby" } %> <%= render "content", locals: { name: "Gorby", friend: "Aaron" } %> def render_content_1(locals) # Locals preamble name = locals[:name] _erbout = +'' _erbout << "

\n Hello, ".freeze _erbout << name.to_s _erbout << "\n

\n".freeze _erbout end def render_content_2(locals) # Locals preamble name = locals[:name] friend = locals[:friend] _erbout = +'' _erbout << "

\n Hello, ".freeze _erbout << name.to_s _erbout << "\n

\n".freeze _erbout end main.html.erb Compiled "content" Unique Preambles

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"This is nice, but what should I do?"

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Always pass the same locals to individual templates.

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The render function

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Finds a Template Compiles the Template Calculates a Method Name Calls the Method

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Find a Template (from the cache) Compiled? Compile the Template Call the method Calculate a Method Name

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Finding a Template

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Template Rendering Depends on "Requested Format"

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Users Controller class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all render "index" end end $ tree app/views/users app/views/users !"" index.html.erb #"" index.xml.erb Controller app/views/users/*

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Template Source

XML template

Users

index.xml.erb index.html.erb

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Requests and Rendering Request Response Template Rendered curl -H 'Accept: application/xml' http:// localhost:3000/users

XML template

index.xml.erb curl http://localhost: 3000/users

Users

index.html.erb curl -H 'Accept: text/ html' http://localhost: 3000/users

Users

index.html.erb

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Template Cache Keys • Local variables • Format • Locale • Variant (iPhone, etc)

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Strange Render Behavior

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Users Controller class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all render "index" end end $ tree app/views/users app/views/users !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb Controller app/views/users/*

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Template Contents

Users

<%= render "my_template" %> I guess this is a png? index.html.erb _my_template.png.erb XML is cool! _my_template.xml.erb

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Requests and Rendering Request Response Template Rendered curl -H 'Accept: application/xml' http://localhost:3000/users Missing XML template Error None curl -H 'Accept: text/html' http://localhost:3000/users Missing HTML partial Error None Browser Missing HTML partial Error None curl http://localhost:3000/users

Users

I guess this is a png? index.html.erb _my_template.png.erb

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Error!!

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Users

I guess this is a png? index.html.erb _my_template.png.erb

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We Can’t Predict

Users

<%= render "my_template" %>

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respond_to Controller class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all render "index" end end class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all respond_to do |format| format.html do render "index" end end end end "Bare" render respond_to render

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Requests and Rendering Request Response Template Rendered curl -H 'Accept: application/ xml' http://localhost:3000/ users Missing XML template Error None curl -H 'Accept: text/html' http://localhost:3000/users Missing HTML partial Error None Browser Missing HTML partial Error None curl http://localhost:3000/ users Missing HTML partial Error None

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Context Dependent

Users

<%= render "my_template" %> class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all render "index" end end class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all respond_to do |format| format.html do render "index" end end end end index.html.erb

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Templates are not "Context Free"

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Prediction and Consistency

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Find a Template (from the cache) Compiled? Compile the Template Call the method Calculate a Method Name Cheap! Cheap! Expensive!

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What Method Will This Call?

Users

<%= render "my_template" %>

Users

<%= render_my_template_00011123abf %> index.html.erb translated template Calls a unique method. But what method?

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Find a Template (from the cache) Compiled? Compile the Template Call the method Calculate a Method Name Cheap! Cheap! Expensive!

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#SPOILER

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Slower Production Boot (but could be eliminated by BootSnap)

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Lower Memory

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Faster Runtime No More "Cache Check" Penalty

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DETOUR!

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Three Templates

<%= render partial: "customer", collection: customers %>

<%= render partial: "customer", collection: customers, cached: true %> _col.html.erb _cached_col.html.erb

Hello: <%= customer.name %>

_customer.html.erb

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Benchmark https://github.com/rails/rails/issues/35257

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Results $ be ruby render_benchmark.rb -- create_table(:customers, {:force=>true}) -> 0.0108s <#ActiveSupport::Cache::MemoryStore entries=1000, size=333893, options={}> Warming up -------------------------------------- collection render: no cache 6.000 i/100ms collection render: with cache 1.000 i/100ms Calculating ------------------------------------- collection render: no cache 65.319 (± 7.7%) i/s - 330.000 in 5.080651s collection render: with cache 11.504 (± 8.7%) i/s - 58.000 in 5.071030s Comparison: collection render: no cache: 65.3 i/s collection render: with cache: 11.5 i/s - 5.68x slower

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I was convinced the cache didn’t work

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I was convinced the cache didn’t work

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I was convinced the cache didn’t work

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I was convinced the cache didn’t work

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But, there were entries in the cache

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BUT AT WHAT COST?

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Proﬁled The Cache ================================== Mode: wall(1000) Samples: 4690 (0.00% miss rate) GC: 207 (4.41%) ================================== TOTAL (pct) SAMPLES (pct) FRAME 594 (12.7%) 594 (12.7%) ActiveModel::LazyAttributeHash#[] 387 (8.3%) 387 (8.3%) ActiveRecord::Transactions#update_attributes_from_transaction_state 1199 (25.6%) 246 (5.2%) ActiveSupport::Cache::Store#expanded_key 301 (6.4%) 218 (4.6%) AbstractController::Caching::Fragments#combined_fragment_cache_key 207 (4.4%) 207 (4.4%) (garbage collection) 932 (19.9%) 196 (4.2%) ActionView::CollectionCaching#collection_by_cache_keys 450 (9.6%) 181 (3.9%) ActiveSupport::Cache::Store#expanded_version

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Cache Key Calculation Was More Expensive Than Template Execution

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Cache Payoff

Hello: <%= customer.name %>

Old Template New Template

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Benchmark Results $ be ruby render_benchmark.rb -- create_table(:customers, {:force=>true}) -> 0.0075s <#ActiveSupport::Cache::MemoryStore entries=1000, size=900893, options={}> Warming up -------------------------------------- collection render: no cache 4.000 i/100ms collection render: with cache 4.000 i/100ms Calculating ------------------------------------- collection render: no cache 41.066 (± 2.4%) i/s - 208.000 in 5.070051s collection render: with cache 43.192 (± 4.6%) i/s - 216.000 in 5.012803s Comparison: collection render: with cache: 43.2 i/s collection render: no cache: 41.1 i/s - same-ish: difference falls within error

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"Cache" doesn’t mean "fast"

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Speeding Up Templates

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Template Static Analysis

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Pre-Compiling Templates https://github.com/jhawthorn/actionview_precompiler/

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ActionviewPrecompiler.precompile

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Static Analysis <%= render "no_locals" %> <%= render "static_locals", locals: { foo: bar } %> <%= render "dynamic_locals", locals: { foo: bar }.merge(baz) %> Can Precompile! Can Precompile! Nope!

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Predicting "Render" Methods

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"Same Format Assumption"

Users

<%= render "my_template" %> <%= render "my_template", format: :png %> $ tree app/views/users app/views/users !"" _my_template.html.erb !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb index.html.erb templates

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Ambiguous Render Problem

Users

<%= render "my_template" %> <%= render "my_template", format: :html %> $ tree app/views/users app/views/users !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb index.html.erb templates Sometimes an exception Sometimes a PNG Always an exception

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"Always Optimize"

Users

<%= render "my_template" %> <%= render "my_template", format: :html %>

Users

<%= render "my_template", format: :png %> <%= render "my_template", format: :html %> index.html.erb index.html.erb

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"Same Format Assumption"

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"Same Format Assumption"

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<%= render "my_template" %> <%= render "my_template", format: :png %>

Users

<%= render_my_template_html_00123abc %> <%= render_my_template_png_00123abc %> index.html.erb Optimized Template

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Ambiguous Render Problem

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Ambiguous Render Problem

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<%= render "my_template" %> <%= render "my_template", format: :html %>

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<%= render "my_template" %> <%= raise MissingTemplateError %> index.html.erb Optimized Template