even faster web sites

Steve [email protected]

http://stevesouders.com/docs/shopping-com-20090520.ppt

Even Faster Web Sites

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 RULES

1. MAKE FEWER HTTP REQUESTS

2. 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

Sept 2007

June 2009

Even Faster Web SitesSplitting the initial payloadLoading scripts without blockingCoupling asynchronous scriptsPositioning inline scriptsSharding dominant domainsFlushing the document earlyUsing iframes sparinglySimplifying CSS Selectors

Understanding Ajax performance..........Doug CrockfordCreating responsive web apps............Ben Galbraith, Dion

AlmaerWriting efficient JavaScript.............Nicholas ZakasScaling with Comet.....................Dylan SchiemannGoing beyond gzipping...............Tony GentilcoreOptimizing images...................Stoyan Stefanov, Nicole

Sullivan

AOLeBayFacebookMySpaceWikipediaYahoo!

Why focus on JavaScript?

YouTube

scripts block

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

7 secs: IE 8, FF 3.5(?), Chr 2, Saf 4http://stevesouders.com/cuzillion/?ex=10008

What's Cuzillion?

9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3

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

Splitting 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

Loading Scripts Without Blocking

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');


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


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


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

parallelization only works in IE

parallel downloads for scripts, nothing else

all document.writes must be in same script block


browser busy indicators

browser busy indicators

good to show busy indicators when the user needs feedback

bad when downloading in the background


*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

asynchronous JS example: menu.js

<script type="text/javascript">var domscript = document.createElement('script');domscript.src = "menu.js"; document.getElementsByTagName('head')

[0].appendChild(domscript);

var aExamples = [ ['couple-normal.php', 'Normal Script Src'], ['couple-xhr-eval.php', 'XHR Eval'], ... ['managed-xhr.php', 'Managed XHR'] ];

function init() { EFWS.Menu.createMenu('examplesbtn', aExamples);}

init();</script>

script DOM element approach

before

after


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

!IE

what about

inlined code that depends on the script?

coupling techniques

hardcoded callback

window onload

timer

degrading script tags

script onload

technique 5: script onload<script type="text/javascript">var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];

function init() { EFWS.Menu.createMenu('examplesbtn', aExamples);}

var domscript = document.createElement('script');domscript.src = "menu.js";

domscript.onloadDone = false;domscript.onload = function() { if ( ! domscript.onloadDone ) { init(); } domscript.onloadDone = true; };domscript.onreadystatechange = function() { if ( "loaded" === domscript.readyState ) { if ( ! domscript.onloadDone ) { init(); } domscript.onloadDone = true; }}

document.getElementsByTagName('head')[0].appendChild(domscript);</script>

pretty nice, medium complexity

asynchronous loading & coupling

async technique: Script DOM Elementeasy, cross-browserdoesn't ensure script order

coupling technique: script onloadfairly easy, cross-browserensures execution order for external

script and inlined code

multiple interdependent external and inline scripts:much more complex (see hidden slides)concatenate your external scripts into

one!

flushing the document early

gotchas:PHP output_buffering – ob_flush()Transfer-Encoding: chunkedgzip – Apache's DeflateBufferSize before

2.2.8proxies and anti-virus softwarebrowsers – Safari (1K), Chrome (2K)

other languages: $| or FileHandle autoflush (Perl), flush

(Python), ios.flush (Ruby)

htmlimageimagescript

htmlimageimagescript call PHP's flush()

flushing and domain blocking

you might need to move flushed resources to a domain different from the HTML dochtml

imageimagescript

htmlimageimagescript

googleimageimagescriptimage204

case study: Google search

blocked by HTML document

different domains

http://www.shopping.com/

http://www.shopping.com/xFS?KW=sony&CLT=SCH

http://www.shopping.com/xPO-Nike_Mens_Super_Bad_Ft_Football_Cleats

http://www.shopping.com

• slow spots:• top – shard CSS and JS, flush• middle – shard images• bottom – scripts (async?)

• use CSS sprites (42 bg images)

• add future Expires header

• optimize images (50K, 20%)

• remove ETags

http://www.shopping.com/xFS?KW=sony&CLT=SCH

• slow spots:• HTML document – flush• bottom – ads (async?, onload?)




• remove ETags

http://www.shopping.com/xPO-Nike_Mens_Super_Bad_Ft_Football_Cleats

• slow spots:• HTML document – flush• top – shard CSS and JS, move CSS above JS

• move inline JS above stylesheet




• remove unused CSS (27K, 20%)

• remove ETags

takeaways

focus on the frontend

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

speed matters

impact on revenue

Google:

Yahoo:

Amazon:

1 http://home.blarg.net/~glinden/StanfordDataMining.2006-11-29.ppt2 http://www.slideshare.net/stoyan/yslow-20-presentation

+500 ms -20% traffic1

+400 ms -5-9% full-page traffic2

+100 ms -1% sales1

cost savings

hardware – reduced load

bandwidth – reduced response size

http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf

if you want better user experience more revenue reduced operating expenses

the strategy is clear

Even Faster Web Sites

Steve [email protected]

http://stevesouders.com/docs/shopping-com-20090520.ppt

even faster web sites

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