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Even Faster Websites

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  1. Even Faster Websites Steve Souders souders@google.com http://stevesouders.com/docs/cbs-20090209.ppt Disclaimer: This content does not necessarily reflect the opinions of my employer.

  2. The Importance of Frontend Performance 9% 91% 17% 83% iGoogle, primed cache iGoogle, empty cache

  3. Time Spent on the Frontend April 2008

  4. 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

  5. 14 Rules • Make fewer HTTP requests • Use a CDN • Add an Expires header • Gzip components • Put stylesheets at the top • Put scripts at 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

  6. YSlow High Performance Web Sites

  7. http://en.oreilly.com/velocity2009 June 22-24, 2009

  8. Even Faster Websites • Split the initial payload • Load scripts without blocking • Don't scatter inline scripts • Couple asynchronous scripts • Split dominant domains • Simplify CSS Selectors • Use iframes sparingly • Flush the document early O'Reilly, Q2 2009

  9. Why focus on JavaScript? Yahoo! Wikipedia eBay AOL MySpace YouTube Facebook

  10. Scripts Block <script src="A.js"> blocks parallel downloads and rendering http://stevesouders.com/cuzillion/?ex=10008 What's "Cuzillion"?

  11. Initial Payload and Execution 26% avg 252K avg

  12. 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?

  13. MSN.com: Parallel Scripts MSN Scripts 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)

  14. Advanced Script Loading XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

  15. XHR Eval varxhrObj = getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; eval(xhrObj.responseText); }; xhrObj.open('GET', 'A.js', true); xhrObj.send(''); script must have same domain as main page must refactor script http://stevesouders.com/cuzillion/?ex=10009

  16. XHR Injection varxhrObj = 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 page http://stevesouders.com/cuzillion/?ex=10015

  17. 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 page • window.frames[0].createNewDiv(); • // access main page from iframe • parent.document.createElement('div'); http://stevesouders.com/cuzillion/?ex=10012

  18. Script DOM Element var 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

  19. 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

  20. document.write Script Tag document.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

  21. Browser Busy Indicators

  22. Browser Busy Indicators good to show busy indicators when the user needs feedback bad when downloading in the background

  23. Ensure/Avoid Ordered Execution • 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 immediately • http://stevesouders.com/cuzillion/?ex=10019

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

  25. and the winner is... XHR Eval XHR Injection Script in iframe Script DOM Element Script Defer same domains different domains Script DOM Element Script Defer no order preserve order XHR Eval XHR Injection Script in iframe Script DOM Element (IE) Script DOM Element (FF) Script Defer (IE) Managed XHR Eval Managed XHR Injection no order preserve order Script DOM Element no busy show busy Script DOM Element (FF) Script Defer (IE) Managed XHR Injection Managed XHR Eval Script DOM Element (FF) Script Defer (IE) Managed XHR Eval Managed XHR Injection no busy show busy XHR Injection XHR Eval Script DOM Element (IE) Managed XHR Injection Managed XHR Eval Script DOM Element

  26. 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?

  27. 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

  28. Examples of Scattered Scripts MSN Wikipedia eBay MySpace

  29. 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

  30. 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 13K+ tests, 9K+ unique testers, 50+ browsers help out by running the test!

  31. Measuring Performance Episodes dev box synthetic testing bucket testing real user data Hammerhead

  32. 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 data load time measurement modal cache clearing combine with bandwidth throttler

  33. CNet Performance Analysis requests: 107 load time: 3.7 secs xfer size: 436K YSlow: F (48) cool • flushed document • HTTP/1.0 downgrade opportunities • load oreo.moo.rb.combined.jsasync • split i.i.com.com across two domains • concatenate 10 scripts • sprite 25 CSS background images • 30 resources with short Expires • 62% (62K) of CSS not used

  34. BNet Performance Analysis requests: 149 load time: 5.9 secs xfer size: 759K YSlow: F (26) cool • flushed document • @import stylesheets opportunities • compress 235K (16 files) • sprite 57 CSS background images • concatenate 12 scripts, 6 stylesheets • optimize images (30K, 16%) • 106 resources with short Expires • 60% (29K) of CSS not used • remove ETags

  35. CBSSports Performance Analysis requests: 99 load time: 8.2 secs xfer size: 689K YSlow: F (31) cool • flushed document opportunities • compress 151K (11 files) • move inline script above stylesheets • concatenate 16 scripts • sprite 26 CSS background images • optimize images (104K, 28%) • move www.cbssports.com images to a CDN • split images.cbssports.com across two domains • almost all resources have a short Expires • 49% (24K) of CSS not used • minify 63K (8 scripts) • remove ETags

  36. Takeaways focus on the frontend run YSlow: http://developer.yahoo.com/yslow this year's focus: JavaScript Split the Initial Payload Load Scripts without Blocking Don't Scatter Inline Scripts speed matters

  37. Impact on Revenue Google: Yahoo: Amazon: +500 ms  -20% traffic1 +400 ms  -5-9% full-page traffic2 +100 ms  -1% sales1 1 http://home.blarg.net/~glinden/StanfordDataMining.2006-11-29.ppt 2 http://www.slideshare.net/stoyan/yslow-20-presentation

  38. Cost Savings hardware – reduced load bandwidth – reduced response size http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf

  39. if you want better user experience more revenue reduced operating expenses the strategy is clear Even Faster Websites

  40. Steve Souders souders@google.com http://stevesouders.com/docs/cbs-20090209.ppt