High Performance Web Sites Tenni Theurer, Yahoo! Engineering Manager http://developer.yahoo.com/performance CSDN-Dr.Dobbs Software Development 2.0 Conference 2007

slow crawl boring snail stagnant unexceptional yawn unresponsive impatient delay moderate blah subdue drag apathetic prolong slack load sluggish sleepy late unexciting reduced lag complex heavy unmemorable obscure why wait perceived response time what is the end user’s experience? performance speed enjoyable urgent instant accelerate perception snap achievement better improve action pleasant pace quick promote swift cool maximum drive prompt advance fast hurry rush satisfying feel exceptional brisk rapid exciting

Exceptional Performance quantify and improve the performance of all Yahoo! products worldwide center of expertise build tools, analyze data gather, research, and evangelize best practices

quantify and improve the performance of all Yahoo! products worldwide

center of expertise

build tools, analyze data

gather, research, and evangelize best practices

Evolution of Performance quantify -> profile -> research, case studies -> best practices -> evangelize -> codify -> rollout -> publicize

quantify

-> profile

-> research, case studies

-> best practices

-> evangelize

-> codify

-> rollout

-> publicize

Today's Checklist perspective on performance turned upside down 3+ actionable takeaways empowered to make everyone's web experience better

perspective on performance turned upside down

3+ actionable takeaways

empowered to make everyone's web experience better

The Importance of Front-End Performance Back-end = 5% Front-end = 95% Even here, front-end = 88%

The Performance Golden Rule 80-90% of the end-user response time is spent on the front-end. Start there. Greater potential for improvement Simpler Proven to work

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

Greater potential for improvement

Simpler

Proven to work

Agenda Performance Research 14 Rules Case Studies Evangelism

Performance Research

14 Rules

Case Studies

Evangelism

Performance Research

Performance Research

http://yuiblog.com/blog/2006/11/28/performance-research-part-1/

Empty vs. Primed Cache empty cache 2.4 seconds primed cache 0.9 seconds 83% fewer bytes 90% fewer HTTP requests

empty cache

2.4 seconds

primed cache

0.9 seconds

83% fewer bytes

90% fewer HTTP requests

http://yuiblog.com/blog/2007/01/04/performance-research-part-2/

Browser Cache Experiment Add a new image to your page <img src= &quot; image/blank.gif &quot; height= &quot; 1 &quot; width= &quot; 1 &quot; /> with the following response headers: Expires: Thu, 15 Apr 2004 20:00:00 GMT Last-Modified: Wed, 28 Sep 2006 23:49:57 GMT } 1 px

Add a new image to your page

<img src= &quot; image/blank.gif &quot; height= &quot; 1 &quot; width= &quot; 1 &quot; />

with the following response headers:

Expires: Thu, 15 Apr 2004 20:00:00 GMT

Last-Modified: Wed, 28 Sep 2006 23:49:57 GMT

Surprising Results 40-60% ~20% page views with empty cache users with empty cache

Experiment Takeaways The empty cache user experience is more prevalent than you think! Optimize for both primed cache and empty cache experience.

The empty cache user experience is more prevalent than you think!

Optimize for both primed cache and empty cache experience.

http://yuiblog.com/blog/2007/03/01/performance-research-part-3

Impact of Cookies on Response Time 80 ms delay dialup users +78 ms 156 ms 3000 bytes +63 ms 141 ms 2500 bytes +47 ms 125 ms 2000 bytes +31 ms 109 ms 1500 bytes +16 ms 94 ms 1000 bytes +1 ms 79 ms 500 bytes 0 ms 78 ms 0 bytes Delta Time Cookie Size keep sizes low

.yahoo.com cookie sizes

http://yuiblog.com/blog/2007/04/11/performance-research-part-4/

Parallel Downloads Two components in parallel per hostname HTTP/1.1 GIF GIF GIF GIF GIF GIF

Maximizing Parallel Downloads response time (seconds) aliases

Maximizing Parallel Downloads response time (seconds) rule of thumb: use at least two but no more than four aliases

Summary What the 80/20 Rule Tells Us about Reducing HTTP Requests http://yuiblog.com/blog/2007/04/11/performance-research-part-4/ Browser Cache Usage – Exposed! http://yuiblog.com/blog/2007/01/04/performance-research-part-2/ When the Cookie Crumbles http://yuiblog.com/blog/2007/01/04/performance-research-part-2/ Maximizing Parallel Downloads in the Carpool Lane http://yuiblog.com/blog/2007/04/11/performance-research-part-4/

What the 80/20 Rule Tells Us about Reducing HTTP Requests

http://yuiblog.com/blog/2007/04/11/performance-research-part-4/

Browser Cache Usage – Exposed!

http://yuiblog.com/blog/2007/01/04/performance-research-part-2/

When the Cookie Crumbles

http://yuiblog.com/blog/2007/01/04/performance-research-part-2/

Maximizing Parallel Downloads in the Carpool Lane

http://yuiblog.com/blog/2007/04/11/performance-research-part-4/

14 Rules

14 Rules

14 Rules Make fewer HTTP requests Use a CDN Add an Expires header Gzip components Put stylesheets at the top Move scripts to the bottom Avoid CSS expressions Make JS and CSS external Reduce DNS lookups Minify JS Avoid redirects Remove duplicate scripts Configure ETags Make AJAX cacheable

Make fewer HTTP requests

Use a CDN

Add an Expires header

Gzip components

Put stylesheets at the top

Move scripts to the bottom

Avoid CSS expressions

Make JS and CSS external

Reduce DNS lookups

Minify JS

Avoid redirects

Remove duplicate scripts

Configure ETags

Make AJAX cacheable

Rule 1: Make fewer HTTP requests CSS sprites combined scripts, combined stylesheets image maps inline images

CSS sprites

combined scripts, combined stylesheets

image maps

inline images

CSS Sprites – Preferred size of combined image is less not supported in Opera 6 http://alistapart.com/articles/sprites <span style=&quot; background-image: url('sprites.gif'); background-position: -260px -90px;&quot;> </span>

size of combined image is less

not supported in Opera 6

Combined Scripts, Combined Stylesheets 3 7 youtube.com 1.5 6.5 Average 1 4 yahoo.com 1 3 wikipedia.org 2 2 myspace.com 1 9 msn.com 1 1 froogle.google.com 2 7 ebay.com 2 11 cnn.com 1 18 aol.com 1 3 amazon.com Stylesheets Scripts

Combined Scripts, Combined Stylesheets combining six scripts into one eliminates five HTTP requests challenges: develop as separate modules number of possible combinations vs. loading more than needed maximize browser cache one solution: dynamically combine and cache

combining six scripts into one eliminates five HTTP requests

challenges:

develop as separate modules

number of possible combinations vs. loading more than needed

maximize browser cache

one solution:

dynamically combine and cache

Rule 2: Use a CDN distribute your static content before distributing your dynamic content youtube.com Akamai yahoo.com wikipedia.org Akamai, Limelight myspace.com SAVVIS msn.com google.com Akamai, Mirror Image ebay.com cnn.com Akamai aol.com Akamai amazon.com

distribute your static content before distributing your dynamic content

Rule 3: Add an Expires header not just for images 26 days 0% 0/7 0/3 0/32 youtube.com 100% 75% 0% 80% 4% 55% 1% 48% 0% % n/a 4/4 1/1 23/23 yahoo.com 1 day 2/3 1/1 6/8 wikipedia.org 1 day 0/2 0/2 0/18 myspace.com 34 days 3/9 1/1 32/35 msn.com 454 days 0/1 0/1 1/23 froogle.google.com 140 days 0/7 0/2 16/20 ebay.com 227 days 2/11 0/2 0/138 cnn.com 217 days 6/18 1/1 23/43 aol.com 114 days 0/3 0/1 0/62 amazon.com Median Age Scripts Stylesheets Images

not just for images

Rule 4: Gzip components you can affect users' download times 90%+ of browsers support compression

you can affect users' download times

90%+ of browsers support compression

Gzip: not just for HTML gzip scripts, stylesheets, XML, JSON (not images, PDF) some some x youtube.com x x x yahoo.com x x x wikipedia.org x x x myspace.com deflate deflate x msn.com x x x froogle.google.com x ebay.com cnn.com some some x aol.com x amazon.com Stylesheets Scripts HTML

gzip scripts, stylesheets, XML, JSON (not images, PDF)

Gzip Edge Cases <1% of browsers have problems with gzip IE 5.5: http://support.microsoft.com/default.aspx?scid=kb;en-us;Q313712 IE 6.0: http://support.microsoft.com/default.aspx?scid=kb;en-us;Q31249 Netscape 3.x, 4.x http://www.schroepl.net/projekte/mod_gzip/browser.htm consider adding Cache-Control: Private remove ETags (Rule 13) hard to diagnose; problem getting smaller

<1% of browsers have problems with gzip

IE 5.5:

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q313712

IE 6.0:

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q31249

Netscape 3.x, 4.x

http://www.schroepl.net/projekte/mod_gzip/browser.htm

consider adding Cache-Control: Private

remove ETags (Rule 13)

hard to diagnose; problem getting smaller

Rule 5: Put stylesheets at the top stylesheets block rendering in IE http://stevesouders.com/examples/css-bottom.php solution: put stylesheets in HEAD (per spec) avoids Flash of Unstyled Content use LINK (not @import)

stylesheets block rendering in IE

http://stevesouders.com/examples/css-bottom.php

solution: put stylesheets in HEAD (per spec)

avoids Flash of Unstyled Content

use LINK (not @import)

Slowest is Fastest CSS at the bottom: resources load faster, but nothing renders CSS at the top: resources take longer, but render progressively @import at the top: same problems as bottom right choice

CSS at the bottom:

resources load faster, but nothing renders

CSS at the top:

resources take longer, but render progressively

@import at the top:

same problems as bottom

Rule 6: Move scripts to the bottom scripts block parallel downloads across all hostnames scripts block rendering of everything below them in the page IE and FF http://stevesouders.com/examples/js-middle.php

scripts block parallel downloads across all hostnames

scripts block rendering of everything below them in the page

IE and FF

http://stevesouders.com/examples/js-middle.php

Rule 6: Move scripts to the bottom script defer attribute is not a solution blocks rendering and downloads in FF slight blocking in IE solution: move them as low in the page as possible

script defer attribute is not a solution

blocks rendering and downloads in FF

slight blocking in IE

solution: move them as low in the page as possible

Rule 7: Avoid CSS expressions used to set CSS properties dynamically in IE width: expression( document.body.clientWidth < 600 ? “ 600px” : “auto” ); problem: expressions execute many times mouse move, key press, resize, scroll, etc. http://stevesouders.com/examples/expression-counter.php

used to set CSS properties dynamically in IE

width: expression(

document.body.clientWidth < 600 ?

“ 600px” : “auto” );

problem: expressions execute many times

mouse move, key press, resize, scroll, etc.

http://stevesouders.com/examples/expression-counter.php

Rule 8: Make JS and CSS external inline: HTML document is bigger external: more HTTP requests, but cached variables page views per user (per session) empty vs. primed cache stats component re-use external is typically better home pages may be an exception

inline: HTML document is bigger

external: more HTTP requests, but cached

variables

page views per user (per session)

empty vs. primed cache stats

component re-use

external is typically better

home pages may be an exception

Post-Onload Download inline in front page download external files after onload window.onload = downloadComponents; function downloadComponents() { var elem = document.createElement(&quot;script&quot;); elem.src = &quot;http://.../file1.js&quot;; document.body.appendChild(elem); ... } speeds up secondary pages

inline in front page

download external files after onload

window.onload = downloadComponents;

function downloadComponents() {

var elem = document.createElement(&quot;script&quot;);

elem.src = &quot;http://.../file1.js&quot;;

document.body.appendChild(elem);

...

}

speeds up secondary pages

Dynamic Inlining start with post-onload download set cookie after components downloaded server-side: if cookie, use external else, do inline with post-onload download cookie expiration date is key speeds up all pages

start with post-onload download

set cookie after components downloaded

server-side:

if cookie, use external

else, do inline with post-onload download

cookie expiration date is key

speeds up all pages

Rule 9: Reduce DNS lookups typically 20-120 ms block parallel downloads OS and browser both have DNS caches

typically 20-120 ms

block parallel downloads

OS and browser both have DNS caches

Rule 10: Minify JavaScript minify inline scripts, too no yes no no yes yes yes no no no Minify External? no www.youtube.com yes www.yahoo.com no www.wikipedia.org no www.myspace.com yes www.msn.com yes froogle.google.com no www.ebay.com no www.cnn.com no www.aol.com no www.amazon.com Minify Inline?

Minify vs. Obfuscate minify – it's safer http://crockford.com/javascript/jsmin http://dojotoolkit.org/docs/shrinksafe not much difference Dojo Savings JSMin Savings Original 21K (25%) 17K (21%) 85K Average 10K (29%) 8K (22%) 34K www.youtube.com 16K (38%) 14K (34%) 42K www.wikipedia.org 24K (28%) 23K (27%) 88K www.myspace.com 24K (25%) 19K (20%) 98K www.cnn.com 4K (10%) 4K (10%) 44K www.aol.com 48K (24%) 31K (15%) 204K www.amazon.com

Rule 11: Avoid redirects 3xx status codes – mostly 301 and 302 HTTP/1.1 301 Moved Permanently Location: http://stevesouders.com/newuri add Expires headers to cache redirects worst form of blocking http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

3xx status codes – mostly 301 and 302

HTTP/1.1 301 Moved Permanently

Location: http://stevesouders.com/newuri

add Expires headers to cache redirects

worst form of blocking

Redirects no yes – secondary page yes – secondary page yes – secondary page yes – initial page no yes – secondary page yes – initial page yes – secondary page no Redirects www.youtube.com www.yahoo.com www.wikipedia.org www.myspace.com www.msn.com froogle.google.com www.ebay.com www.cnn.com www.aol.com www.amazon.com

Rule 12: Remove duplicate scripts hurts performance extra HTTP requests (IE only) extra executions atypical? 2 of 10 top sites contain duplicate scripts team size, # of scripts

hurts performance

extra HTTP requests (IE only)

extra executions

atypical?

2 of 10 top sites contain duplicate scripts

team size, # of scripts

Rule 13: Configure ETags unique identifier returned in response ETag: &quot;c8897e-aee-4165acf0&quot; Last-Modified: Thu, 07 Oct 2004 20:54:08 GMT used in conditional GET requests If-None-Match: &quot;c8897e-aee-4165acf0&quot; If-Modified-Since: Thu, 07 Oct 2004 20:54:08 GMT if ETag doesn't match, can't send 304

unique identifier returned in response

ETag: &quot;c8897e-aee-4165acf0&quot;

Last-Modified: Thu, 07 Oct 2004 20:54:08 GMT

used in conditional GET requests

If-None-Match: &quot;c8897e-aee-4165acf0&quot;

If-Modified-Since: Thu, 07 Oct 2004 20:54:08 GMT

if ETag doesn't match, can't send 304

The Problem with ETags ETag format Apache: inode -size-timestamp IIS: Filetimestamp: ChangeNumber ETag for a single entity differs across servers, by default Sites with >1 server return too few 304s ((n-1)/n)% wasted downloads Remove them Apache: FileETag none IIS: http://support.microsoft.com/kb/922703/

ETag format

Apache: inode -size-timestamp

IIS: Filetimestamp: ChangeNumber

ETag for a single entity differs across servers, by default

Sites with >1 server return too few 304s

((n-1)/n)% wasted downloads

Remove them

Apache: FileETag none

IIS: http://support.microsoft.com/kb/922703/

Rule 14: Make AJAX cacheable XHR, JSON, iframe, dynamic scripts can still be cached (and minified, and gzipped) a personalized response should still be cacheable for that person

XHR, JSON, iframe, dynamic scripts can still be cached (and minified, and gzipped)

a personalized response should still be cacheable for that person

AJAX Example: Yahoo! Mail Beta address book XML request -> GET /yab/[...]&r=0.5289571053069156 HTTP/1.1 Host: us.xxx.mail.yahoo.com ← HTTP/1.1 200 OK Date: Thu, 12 Apr 2007 19:39:09 GMT Cache-Control: private,max-age=0 Last-Modified: Sat, 31 Mar 2007 01:17:17 GMT Content-Type: text/xml; charset=utf-8 Content-Encoding: gzip address book changes infrequently cache it; add last-modified-time in URL

address book XML request

-> GET /yab/[...]&r=0.5289571053069156 HTTP/1.1

Host: us.xxx.mail.yahoo.com

← HTTP/1.1 200 OK

Date: Thu, 12 Apr 2007 19:39:09 GMT

Cache-Control: private,max-age=0

Last-Modified: Sat, 31 Mar 2007 01:17:17 GMT

Content-Type: text/xml; charset=utf-8

Content-Encoding: gzip

address book changes infrequently

cache it; add last-modified-time in URL

Case Studies

Case Studies

Case Study: move JS to onload remove bottom tabs avoid redirects image sprites host JS on CDN combine JS files 40-50%

move JS to onload

remove bottom tabs

avoid redirects

image sprites

host JS on CDN

combine JS files

Preloading 5 4 2 b be bec beck beckh beckha beckham Download Search components: ysch_srp_20070319.js yschx_20070320a.css flat2_search.gif dropdown.gif bulb1.gif ar_next.gif addmy.gif 3 1

Download Search components:

ysch_srp_20070319.js yschx_20070320a.css

flat2_search.gif

dropdown.gif

bulb1.gif

ar_next.gif

addmy.gif

What about performance and Web 2.0 apps? client-side CPU is more of an issue user expectations are higher these rules still apply, new rules will come out start off on the right foot

client-side CPU is more of an issue

user expectations are higher

these rules still apply, new rules will come out

start off on the right foot

Case Study: Mail Mail Classic User Workflow mail.yahoo.com view inbox folder read messages (x3) compose message confirm send total time: Time 2.40 s 4.98 s 6.39 s 2.21 s 2.10 s 18.08 s Time 12.48 s 1.52 s 1.53 s 0.34 s 0s 15.87 s Delta +420% -70% -76% -85% -100% -12%

Evangelism Book High Performance Web Sites Conferences Yahoo! F2E Summit Web 2.0 Expo Rich Web Experience CSDN-Dr. Dobbs Blogs YUI Blog: http://yuiblog.com/blog/category/performance YDN Blog: http://developer.yahoo.com/performance/ Open Source YSlow OSCon Ajax Experience Blogher Future of Web Apps

Book

High Performance Web Sites

Conferences

Yahoo! F2E Summit

Web 2.0 Expo

Rich Web Experience

CSDN-Dr. Dobbs

Blogs

YUI Blog: http://yuiblog.com/blog/category/performance

YDN Blog: http://developer.yahoo.com/performance/

Open Source YSlow

OSCon

Ajax Experience

Blogher

Future of Web Apps

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

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

Ten Top U.S Web Sites 139K 178K 106K 205K 221K 18K 275K 502K 182K 405K Page Weight 9.6 sec 5.9 sec 6.2 sec 7.8 sec 9.3 sec 1.7 sec 9.6 sec 22.4 sec 11.5 sec 15.9 sec Response Time D www.youtube.com A www.yahoo.com C www.wikipedia.org D www.myspace.com F www.msn.com A froogle.google.com C www.ebay.com F www.cnn.com F www.aol.com D www.amazon.com YSlow Grade

Conclusion

Conclusion

Takeaways focus on the front-end harvest the low-hanging fruit you do control user response times small investment up front keeps on giving LOFNO – be an advocate for your users

focus on the front-end

harvest the low-hanging fruit

you do control user response times

small investment up front keeps on giving

LOFNO – be an advocate for your users

Today's Checklist perspective on performance turned upside down 3+ actionable takeaways empowered to make everyone's web experience better

perspective on performance turned upside down

3+ actionable takeaways

empowered to make everyone's web experience better

Tenni Theurer [email_address]

CC Images Used &quot;Need for Speed&quot; by Amnemon: http://www.flickr.com/photos/marinacvinhal/379111290/ &quot;Max speed 15kmh&quot; by xxxtoff: http://www.flickr.com/photos/xxxtoff/219781763/ &quot;maybe&quot; by Tal Bright: http://www.flickr.com/photos/bright/118197469/ &quot;takeout&quot; by dotpolka: http://www.flickr.com/photos/dotpolka/249129144/ &quot;how do they do that&quot; by Fort Photo: http://www.flickr.com/ photos/fortphoto/388825145 / &quot;Absolutely Nothing is Allowed Here&quot; by Vicki & Chuck Rogers: http://www.flickr.com/photos/two-wrongs/205467442/ &quot;Zipper Pocket&quot; by jogales: http://www.flickr.com/photos/jogales/11519576/ &quot;new briefcase&quot; by dcJohn: http://www.flickr.com/photos/dcjohn/85504455/ &quot;Told you it was me!&quot; by Pug!: http://flickr.com/photos/pugspace/1277023154/ &quot;Robert's Legion&quot; by dancharvey: http://www.flickr.com/photos/dancharvey/2647529/ &quot;thank you&quot; by nj dodge: http://flickr.com/photos/nj_dodge/187190601/

&quot;Need for Speed&quot; by Amnemon: http://www.flickr.com/photos/marinacvinhal/379111290/

&quot;Max speed 15kmh&quot; by xxxtoff: http://www.flickr.com/photos/xxxtoff/219781763/

&quot;maybe&quot; by Tal Bright: http://www.flickr.com/photos/bright/118197469/

&quot;takeout&quot; by dotpolka: http://www.flickr.com/photos/dotpolka/249129144/

&quot;how do they do that&quot; by Fort Photo: http://www.flickr.com/ photos/fortphoto/388825145 /

&quot;Absolutely Nothing is Allowed Here&quot; by Vicki & Chuck Rogers: http://www.flickr.com/photos/two-wrongs/205467442/

&quot;Zipper Pocket&quot; by jogales: http://www.flickr.com/photos/jogales/11519576/

&quot;new briefcase&quot; by dcJohn: http://www.flickr.com/photos/dcjohn/85504455/

&quot;Told you it was me!&quot; by Pug!: http://flickr.com/photos/pugspace/1277023154/

&quot;Robert's Legion&quot; by dancharvey: http://www.flickr.com/photos/dancharvey/2647529/

&quot;thank you&quot; by nj dodge: http://flickr.com/photos/nj_dodge/187190601/