1.High Performance Web Sites 14 rules for faster-loading pages Steve Souders [email_address] Tenni Theurer [email_address]

2.

Introduction

3. Exceptional Performance

started in 2004

quantify and improve the performance of all Yahoo! products worldwide

center of expertise

build tools, analyze data

gather, research, and evangelize best practices

4. Scope

performance breaks into two categories

• response time

• efficiency

current focus is response time

of web products

5. Rough Cuts: now Hardcopy: Summer 2007 http://www.oreilly.com/catalog/9780596514211/ 6. The Importance of Front-End Performance 7. Back-end vs. Front-end percentage of time spent on the front-end 95% 97% youtube.com 88% 95% yahoo.com 88% 80% wikipedia.org 86% 96% myspace.com 95% 97% msn.com 64% 86% google.com 92% 98% ebay.com 92% 81% cnn.com 86% 94% aol.com 86% 82% amazon.com Full Cache Empty Cache 8. 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

9. Schedule

Performance Research

break

14 Rules

break

Case Studies

Live Analysis

10.

Performance Research

11. slow crawl boring snail stagnant unexceptional yawn unresponsive impatient delay moderate blah subdue drag apathetic prolong slack load sluggish sleepy late unexciting reduced lag complexheavy unmemorable obscure whywait perceived response time what is the end users experience? performancespeedenjoyableurgent instant accelerate perceptionsnapachievementbetter improve actionpleasantpace quickpromote swift cool maximum drive promptadvancefasthurry rush satisfyingfeelexceptional brisk rapidexciting 12. User Perception

Usability and perception are important for performance.

The users perception is more relevant than actual unload-to-onload response time.

Definition of "user onload" is undefined or varies from one web page to the next.

13. http://yuiblog.com/blog/2006/11/28/performance-research-part-1/ 14. 80/20 Performance Rule

Vilfredo Pareto:

80% of consequences come from 20% of causes

Focus on the 20% that affects 80% of the end-user response time.

Start at the front-end.

15. Empty vs. Full Cache 1 user requests www.yahoo.com 2 user requests other web pages 3 user re-requests www.yahoo.com 16. Empty vs. Full Cache with an empty cache 1 user requests www.yahoo.com 2 user requests other web pages 3 user re-requests www.yahoo.com 17. Empty vs. Full Cache 1 user requests www.yahoo.com 2 user requests other web pages 3 user re-requests www.yahoo.com 18. Empty vs. Full Cache Expires header 3 user re-requests www.yahoo.com with a full cache 1 user requests www.yahoo.com 2 user requests other web pages 19. Empty vs. Full Cache

empty cache

2.4 seconds

full cache

0.9 seconds

83% fewer bytes

90% fewer HTTP requests

20. How much does this benefit our users?

It depends on how many users have components in cache.

What percentage ofusersview a page with an empty cache * ?

*Empty cache means the browser has to request the components instead of pulling them from the browser disk cache.

What percentage ofpage views are done with an empty cache * ?

21. http://yuiblog.com/blog/2007/01/04/performance-research-part-2/ 22. Browser Cache Experiment

Add a new image to your page

with the following response headers:

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

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

} 1px 23. Browser Cache Experiment

Requests from the browser will have one of these response status codes:

• 200 The browser does not have the imagein its cache.

• 304 The browser has the image in its cache,but needs to verify the last modified date.

24. Browser Cache Experiment total # of 200 responses # of 200 + # of 304 responses What percentage ofpage viewsare done with an empty cache? # unique users with at least one 200 response total # unique users What percentage ofusersview with an empty cache? } 1px 25. Surprising Results 40-60%~20%page views with empty cache users with empty cache 26. Experiment Takeaways

Keep in mind the empty cache user experience. It might be more prevalent than you think!

Use different techniques to optimize full versus empty cache experience.

27. http://yuiblog.com/blog/2007/03/01/performance-research-part-3 28. HTTP Quick Review HTTP response header sent by the web server: HTTP/1.1 200 OK Content-Type: text/html; charset=utf-8 Set-Cookie: C=abcdefghijklmnopqrstuvwxyz; domain=.yahoo.com 1 user requests www.yahoo.com 29. HTTP Quick Review HTTP request header sent by the browser: GET / HTTP/1.1 Host: finance.yahoo.com User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Cookie: C=abcdefghijklmnopqrstuvwxyz; 1 user requests www.yahoo.com 2 user requests finance.yahoo.com 30. HTTP Quick Review HTTP request header sent by the browser: GET / HTTP/1.1 Host: autos.yahoo.com User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Cookie:C=abcdefghijklmnopqrstuvwxyz ; 1 user requests www.yahoo.com 3 user requests autos.yahoo.com 31. HTTP Quick Review HTTP request header sent by the browser: GET / HTTP/1.1 Host: mail.yahoo.com User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Cookie: C=abcdefghijklmnopqrstuvwxyz; 1 user requests www.yahoo.com 4 user requests mail.yahoo.com 32. HTTP Quick Review HTTP request header sent by the browser: GET / HTTP/1.1 Host: tech.yahoo.com User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Cookie: C=abcdefghijklmnopqrstuvwxyz; 1 user requests www.yahoo.com 5 user requests tech.yahoo.com 33. 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 34. .yahoo.com cookie sizes 35. Analysis of Cookie Sizes across the Web 500 bytes MySpace 331 bytes eBay 268 bytes MSN 218 bytes YouTube 184 bytes CNN 122 bytes Yahoo 72 bytes Google 60 bytes Amazon Total Cookie Size 36. Experiment Takeaways

eliminate unnecessary cookies

keep cookie sizes low

set cookies at appropriate domain level

set Expires date appropriately

• earlier date or none removes cookie sooner

37. http://yuiblog.com/blog/2007/04/11/performance-research-part-4/ 38. Parallel Downloads Two components in parallel per hostname HTTP/1.1 GIF GIF GIF GIF GIF GIF 39. Parallel Downloads Two in parallel Four in parallel Eight in parallel 40. Maximizing Parallel Downloads response time (seconds) aliases 41. Maximizing Parallel Downloads response time (seconds) aliases 42. Maximizing Parallel Downloads response time (seconds) aliases 43. Maximizing Parallel Downloads response time (seconds) rule of thumb: use at least two but no more than four aliases 44. Experiment Takeaways

consider the effects of CPU thrashing

DNS lookup times vary across ISPs and geographic locations

domain names may not be cached

45. 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/

46.

14 Rules

47. 14 Rules

Make fewer HTTP requests

Use a CDN

Add an Expires header

Gzip components

Put CSS at the top

Move JS to the bottom

Avoid CSS expressions

Make JS and CSS external

Reduce DNS lookups

Minify JS

Avoid redirects

Remove duplicate scripts

Turn off ETags

Make AJAX cacheable and small

48. Rule 1: Make fewer HTTP requests

image maps

CSS sprites

inline images

combined scripts, combined stylesheets

49. Image maps

server-side

->http://.../navbar.cgi?127,13

client-side preferred

drawbacks:

• must be contiguous

• defining area coordinates tedious, errors

http://www.w3.org/TR/html401/struct/objects.html#h-13.6 50. CSS Sprites Preferred

size of combined image is less

not supported in Opera 6

http://alistapart.com/articles/sprites 51. Inline Images

data:URL scheme

• data:[][;base64],

SRC="data:image/gif;base64,R0lGODlhDAAMALMLAPN8ffBiYvWWlvrKy/FvcPewsO9VVfajo+w6O/zl5estLv/8/AAAAAAAAAAAAAAAACH5BAEAAAsALAAAAAAMAAwAAAQzcElZyryTEHyTUgknHd9xGV+qKsYirKkwDYiKDBiatt2H1KBLQRFIJAIKywRgmhwAIlEEADs=">

not supported in IE

avoid increasing size of HTML pages:

• put inline images in cached stylesheets

http://tools.ietf.org/html/rfc2397 52. 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 53. 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

54. 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 55. 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 56. Rule 4: Gzip components

youcanaffect users' download times

90%+ of browsers support compression

57. Gzip vs. Deflate Gzip compresses more Gzip supported in more browsers Deflate Gzip 67% 4.7K 73% 3.7K 14.1K Stylesheet 52% 0.5K 56% 0.4K 1.0K Stylesheet 58% 16.6K 64% 14.5K 39.7K Script 66% 1.1K 67% 1.1K 3.3K Script Savings Size Savings Size Size 58. 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 59. Gzip Configuration

Apache 2.x: mod_deflate

• AddOutputFilterByType DEFLATE text/html text/css application/x-javascript

HTTP request

• Accept-Encoding: gzip, deflate

HTTP response

• Content-Encoding: gzip

• Vary: Accept-Encoding

needed for proxies 60. Gzip Edge Cases