Steve Souderssouders@google.com

http://stevesouders.com/docs/facebook-20081030.ppt

Life's too short,write fast code

part 1

Disclaimer: This content does not necessarily reflect the opinions of my employer.

17%

83%

iGoogle, primed cache

The Importance of Frontend Performance

9% 91%

iGoogle, empty cache

Time Spent on the Frontend

Empty Cache

Primed Cache

www.aol.com 97% 97%

www.ebay.com 95% 81%

www.facebook.com 95% 81%

www.google.com/search

47% 0%

search.live.com/results 67% 0%

www.msn.com 98% 94%

www.myspace.com 98% 98%

en.wikipedia.org/wiki 94% 91%

www.yahoo.com 97% 96%

www.youtube.com 98% 97%April 2008

The Performance Golden Rule

80-90% of the end-user response time is spent on the frontend. Start there.

greater potential for improvement

simpler

proven to work

14 Rules1. Make fewer HTTP

requests2. Use a CDN3. Add an Expires header4. Gzip components5. Put stylesheets at the

top6. Put scripts at the

bottom7. Avoid CSS expressions8. Make JS and CSS

external9. Reduce DNS lookups10.Minify JS11.Avoid redirects12.Remove duplicate

scripts13.Configure ETags14.Make AJAX cacheable

High Performance Web Sites

YSlow

http://conferences.oreilly.com/velocity/ June 22-24, 2009

High Performance Web Sites, Vol 2

1. Split the initial payload2. Load scripts without blocking3. Don't scatter inline scripts4. Split dominant domains5. Make static content cookie-free6. Reduce cookie weight7. Minify CSS8. Optimize images9. Use iframes sparingly10.To www or not to www

}part 1

AOLeBayFacebookMySpaceWikipediaYahoo!

Why focus on JavaScript?

YouTube

Scripts Block

<script src="A.js"> blocks parallel downloads and rendering

What's "Cuzillion"?

http://stevesouders.com/cuzillion/?ex=10008

JavaScript

Functions Executed before

onload

www.aol.com 115K 30%

www.ebay.com 183K 44%

www.facebook.com 1088K 9%

www.google.com/search

15K 45%

search.live.com/results

17K 24%

www.msn.com 131K 31%

www.myspace.com 297K 18%

en.wikipedia.org/wiki 114K 32%

www.yahoo.com 321K 13%

www.youtube.com 240K 18%

26% avg252K avg

Initial Payload and Execution

Split the initial payload

split your JavaScript between what's needed to render the page and everything else

load "everything else" after the page is rendered

separate manually (Firebug); tools needed to automate this (Doloto from Microsoft)

load scripts without blocking – how?

MSNScripts and other resources downloaded in parallel! How? Secret sauce?!var p= g.getElementsByTagName("HEAD")[0];var c=g.createElement("script");c.type="text/javascript";c.onreadystatechange=n;c.onerror=c.onload=k;c.src=e;p.appendChild(c)

MSN.com: Parallel Scripts

Advanced Script Loading

XHR Eval

XHR Injection

Script in Iframe

Script DOM Element

Script Defer

document.write Script Tag

XHR Eval

script must have same domain as main page

must refactor script

var xhrObj = getXHRObject();xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; eval(xhrObj.responseText); };xhrObj.open('GET', 'A.js', true);xhrObj.send('');

http://stevesouders.com/cuzillion/?ex=10009

XHR Injectionvar xhrObj = getXHRObject();xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; var se=document.createElement('script'); document.getElementsByTagName('head') [0].appendChild(se); se.text = xhrObj.responseText; };xhrObj.open('GET', 'A.js', true);xhrObj.send('');

script must have same domain as main pagehttp://stevesouders.com/cuzillion/?ex=10015

Script in Iframe<iframe src='A.html' width=0 height=0 frameborder=0 id=frame1></iframe>

iframe must have same domain as main page

must refactor script:// access iframe from main pagewindow.frames[0].createNewDiv();

// access main page from iframeparent.document.createElement('div');

http://stevesouders.com/cuzillion/?ex=10012

Script DOM Elementvar se = document.createElement('script');se.src = 'http://anydomain.com/A.js';document.getElementsByTagName('head')[0].appendChild(se);

script and main page domains can differ

no need to refactor JavaScript

http://stevesouders.com/cuzillion/?ex=10010

Script Defer<script defer src='A.js'></script>

only supported in IE (just landed in FF 3.1)

script and main page domains can differ

no need to refactor JavaScript

http://stevesouders.com/cuzillion/?ex=10013

document.write Script Tagdocument.write("<scr" + "ipt type='text/javascript' src='A.js'>" + "</scr" + "ipt>");

parallelization only works in IE

parallel downloads for scripts, nothing else

all document.writes must be in same script block

http://stevesouders.com/cuzillion/?ex=10014

Browser Busy Indicators

Browser Busy Indicators

good to show busy indicators when the user needs feedback

bad when downloading in the background

Ensure scripts execute in order:necessary when scripts have dependencies

IE: http://stevesouders.com/cuzillion/?ex=10017

FF: http://stevesouders.com/cuzillion/?ex=10018

Avoid scripts executing in order:faster – first script back is executed

immediatelyhttp://stevesouders.com/cuzillion/?ex=10019

Ensure/Avoid Ordered Execution

Summary of Traits

*Only other document.write scripts are downloaded in parallel (in the same script block).

and the winner is...XHR EvalXHR InjectionScript in iframeScript DOM ElementScript Defer

Script DOM ElementScript Defer

Script DOM Element

Script DOM Element (FF)Script Defer (IE)

XHR EvalXHR InjectionScript in iframeScript DOM Element (IE)

XHR InjectionXHR EvalScript DOM Element (IE)

Managed XHR InjectionManaged XHR EvalScript DOM Element

Managed XHR InjectionManaged XHR Eval

Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection

Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection

different domains same domains

no order

preserve order

no order

no busyshow busy

show busyno busy

preserve order

Load Scripts without Blocking

don't let scripts block other downloads

you can still control execution order, busy indicators, and onload event

What about inline scripts?

Inline Scripts after Stylesheets Block Downloading

Firefox 3 and IE download stylesheets in parallel

...unless the stylesheet is followed by an inline script

http://stevesouders.com/cuzillion/?ex=10021

best to move inline scripts above stylesheets or below other resources

use Link, not @import

eBayMSNMySpaceWikipedia

Examples of Scattered Scripts

Don't Scatter Inline Scripts

remember inline scripts carry a cost

avoid long-executing inline scripts

don't put inline scripts between stylesheets and other resources

Announcement 1: UA Profiler

tracks browser performance traits

http://stevesouders.com/ua/

go to the test page

your browser automatically walks through the tests (requires JS)

results recorded and shared publicly

currently 2K+ tests, 1K+ unique testers, 100+ browsers

help out by running the test!

Measuring Performance

Episodes

dev box synthetic testing

bucket testing

real user data

Hammerhead

Announcement 2: Hammerhead

"moving performance testing upstream"http://stevesouders.com/hammerhead/

Firebug extension

load M URLs N times, empty & primed cache

record average & median time

add'l features: export dataload time measurementmodal cache clearing

combine with bandwidth throttler

Facebook Performance Analysis

the good– CDN (Akamai)– future Expires header (~10 days)– gzip turned on– stylesheets at the top (pretty much)– few CSS expressions (4)– JavaScript is minified– no redirects– few ETags (only profile photos)

1. move js below css2. shard across 2 domains3. combine scripts, load async, move lower4. sprite CSS background images5. prefetch resources for next page

1

2

3

4

5

2

Welcome

Home

~150 requests~1M JavaScript

(uncompr)~300K CSS (uncompr)

Home

1. move js below css2. combine stylesheets3. combine scripts, load async, move lower4. sprite CSS background images!!5. reduce size of JS – 85% not used by onload6. reduce size of CSS – 81% (240K) not used by

onload7. optimize images – 44% (97K) lossless

(smushit.com)8. reduce DNS lookups – 15 domains!9. remove ETags on profile photos

Takeaways

focus on the frontend

run YSlow: http://developer.yahoo.com/yslow

this year's focus: JavaScriptSplit the Initial PayloadLoad Scripts without BlockingDon't Scatter Inline Scripts

speed matters

life's too short, write fast code

Steve Souderssouders@google.com

http://stevesouders.com/docs/facebook-20081030.ppt