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Even Faster Web Sites
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  1. Even Faster Web Sites http://stevesouders.com/docs/velocity-20090622.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. Sept 2007

  6. June 2009

  7. 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 14 Rules

  8. Even Faster Web Sites Splitting the initial payload Loading scripts without blocking Coupling asynchronous scripts Positioning inline scripts Sharding dominant domains Flushing the document early Using iframes sparingly Simplifying CSS Selectors Understanding Ajax performance..........Doug Crockford Creating responsive web apps............Ben Galbraith, Dion Almaer Writing efficient JavaScript.............Nicholas Zakas Scaling with Comet.....................Dylan Schiemann Going beyond gzipping...............Tony Gentilcore Optimizing images...................Stoyan Stefanov, Nicole Sullivan

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

  10. scripts block <script src="A.js"> blocks parallel downloads and rendering 9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3 7 secs: IE 8, FF 3.5(?), Chr 2, Saf 4 http://stevesouders.com/cuzillion/?ex=10008 What's Cuzillion?

  11. Splitting the Initial Payload 26% avg 252K avg

  12. 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?

  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. Loading Scripts Without Blocking XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag

  15. 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

  16. browser busy indicators

  17. Loading Scripts Without Blocking *Only other document.write scripts are downloaded in parallel (in the same script block).

  18. 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

  19. asynchronous JS example: menu.js script DOM element approach • <script type="text/javascript"> • vardomscript = document.createElement('script'); • domscript.src = "menu.js"; • document.getElementsByTagName('head')[0].appendChild(domscript); • varaExamples = • [ • ['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>

  20. before after

  21. Loading Scripts Without Blocking !IE *Only other document.write scripts are downloaded in parallel (in the same script block).

  22. what about • inlined code • that depends on the script?

  23. coupling techniques • hardcoded callback • window onload • timer • degrading script tags • script onload

  24. technique 5: script onload • <script type="text/javascript"> • varaExamples = [['couple-normal.php', 'Normal Script Src'], ...]; • function init() { • EFWS.Menu.createMenu('examplesbtn', aExamples); • } • vardomscript = 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

  25. asynchronous loading & coupling • async technique: Script DOM Element • easy, cross-browser • doesn't ensure script order • coupling technique: script onload • fairly easy, cross-browser • ensures 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!

  26. bad: stylesheet followed by inline script • browsers download stylesheets in parallel with other resources that follow... • ...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

  27. Positioning Inline Scripts MSN Wikipedia eBay MySpace

  28. Sharding Dominant Domains • but Rule 9 says "Reduce DNS lookups"?! • remove DNS lookups that aren't heavily used • split domains that are on the critical path • how find "critical path"?

  29. www.yahoo.com

  30. news.google.com http://news.google.com

  31. connections per server by browser • newer browsers open more connections* • best to shard across 2-4 domains** * http://www.stevesouders.com/blog/2008/03/20/roundup-on-parallel-connections/ ** http://yuiblog.com/blog/2007/04/11/performance-research-part-4/

  32. flushing the document early • gotchas: • PHP output_buffering – ob_flush() • Transfer-Encoding: chunked • gzip – Apache's DeflateBufferSize before 2.2.8 • proxies and anti-virus software • browsers – Safari (1K), Chrome (2K) • HTML document blocks resources • other languages: • $| or FileHandleautoflush (Perl), flush (Python), ios.flush (Ruby) html image image script call PHP's flush() html image image script

  33. successful flushing • Google Search • external resource downloaded early • content visible to the user http://www.google.com/images/nav_logo4.png google image image script image 204

  34. Using Iframes Sparingly • most expensive DOM element • blocks parent's onload • workaround: set iframe src via setTimeout <iframe id=if1 src=""></iframe> <script type="text/javascript"> function setSrc() { document.getElementById('if1').src="url"; } setTimeout(setSrc, 0); </script>

  35. types of CSS selectors • ID selectors: #toc {} • class selectors: .chapter {} • type selectors: A {} • adjacent sibling selectors: H1 + #toc {} • child selectors: #toc > LI {} • descendant selectors: #toc A {} • universal selectors: * {} • attribute selectors: href="#index"] {} • psuedo classes and elements: A:hover {}

  36. writing efficient CSS https://developer.mozilla.org/en/Writing_Efficient_CSS • "The style system matches a rule by starting with the rightmost selector and moving to the left through the rule's selectors. As long as your little subtree continues to check out, the style system will continue moving to the left until it either matches the rule or bails out because of a mismatch." • #toc > LI { font-weight: bold; } find every LI whose parent is id="toc" • #toc A { color: #444; } find every A and climb its ancestors until id="toc" or DOM root (!) is found

  37. real world levels of CSS

  38. testing typical CSS 1K rules (vs. 20K) same amount of CSS in all test pages 30 ms avg delta • "costly"selectors aren't always costly (at typical levels) • are these selectors "costly"? • DIV DIVDIV P A.class0007 { ... } http://www.stevesouders.com/blog/2009/03/10/performance-impact-of-css-selectors/

  39. testing expensive selectors 1K rules (vs. 20K) same amount of CSS in all test pages 2126 ms avg delta! truly expensive selector A.class0007 * { ... } • compare to: • DIV DIVDIV P A.class0007 { ... } the key is the key selector – the rightmost argument

  40. Simplifying CSS Selectors • efficient CSS comes at a cost – page weight • focus optimization on selectors where the key selector matches many elements • reduce the number of selectors

  41. Performance Tools • HttpWatch http://www.httpwatch.com/ • Firebug http://getfirebug.com/ • Page Speed http://code.google.com/speed/page-speed/ • YSlow http://developer.yahoo.com/yslow/ • Smush.ithttp://smush.it/ • CSS Sprite Generator http://spritegen.website-performance.org/ • SpriteMehttp://spriteme.org/ (in progress) • Hammerheadhttp://stevesouders.com/hammerhead/ • Cuzillion http://cuzillion.com/

  42. Performance Analyzers: HPWS rules

  43. Performance Analyzers: EFWS rules

  44. Performance Analyzers: other rules

  45. Top 10 Performance * YSlow wouldn't start.

  46. Wikipedia • combine 6 scripts, 8 stylesheets • add Expires header • minify JavaScript, save 39K (36%) • avoid inline script after stylesheet • 31K (41%) unused CSS • remove ETags