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Slide 1: High Performance Web Pages Stoyan Stefanov Yahoo! Exceptional Performance http://developer.yahoo.com/performance PHP Quebec, March 13, 2008 PHP Quebec 2008 • Page 1

Slide 2: The sluggish Web • We’re getting used to the web as a tool for our day-to-day tasks • We all want a nice user experience • We won’t tolerate slow pages (we have options) • 500 ms slower = 20% drop in traffic (Google) • 100 ms slower = 1% drop in sales (Amazon) PHP Quebec 2008 • Page 2

Slide 3: This talk • How to improve page performance • Focus on the front-end • 14 best practices for faster pages • … and 20 more! PHP Quebec 2008 • Page 3

Slide 4: Exceptional Performance at Yahoo! • Quantify and improve the performance of all Yahoo! products worldwide • Center of expertise • Build tools, analyze data • Gather, research, and evangelize best practices - internally and externally PHP Quebec 2008 • Page 4

Slide 5: PHP Quebec 2008 • Page 5

Slide 6: The Importance of Front-End Performance Back- Front- end=5% end=95% 88% Even here, front-end=

Slide 7: Focus on the front-end • 80-90% of the time • Easier than the back-end • Proven to work PHP Quebec 2008 • Page 7

Slide 8: List of 14 best practices (updated) 1. Make Fewer HTTP Requests content 2. Use a Content Delivery Network server 3. Add Expires header (or Cache-control) server 4. Gzip Components server 5. Put CSS at the Top css 6. Move Scripts to the Bottom (inline too) javascript 7. Avoid CSS Expressions css 8. Make JavaScript and CSS External css javascript 9. Reduce DNS Lookups content 10.Minify JavaScript and CSS (inline too) css javascript 11.Avoid Redirects content 12.Remove Duplicate Scripts javascript 13.Configure ETags server 14.Make AJAX Cacheable content http://developer.yahoo.com/performance/rules.html PHP Quebec 2008 • Page 8

Slide 9: YSlow • Yahoo!’s performance lint tool • Extension to the Firebug extension to Firefox • Checks for compliance with the best practices • Grades (offends) http://developer.yahoo.com/yslow/ PHP Quebec 2008 • Page 9

Slide 10: PHP Quebec 2008 • Page 10

Slide 11: The Life of Page 2.0 event handlers, backend fetching components, user interaction, XHRs components XHRs request request HTML page onload settles sent graduation marriage? R.I.P. conception birth fetus child User perceived “onload” teen happens somewhere here adult PHP Quebec 2008 • Page 11

Slide 12: After YSlow "A"? server 1. Flush the buffer early server 2. Use GET for AJAX requests content 3. Post-load components content 4. Preload components content 5. Reduce the number of DOM elements content 6. Split components across domains content 7. Minimize the number of iframes content 8. No 404s cookie 9. Reduce cookie size cookie 10. Use cookie-free domains for components javascript 11. Minimize DOM access 12. Develop smart event handlers javascript 13. Choose <link> over @import css 14. Avoid filters css 15. Optimize images images 16. Optimize CSS sprites images 17. Don't scale images in HTML images 18. Make favicon.ico small and cacheable images 19. Keep components under 25K mobile 20. Pack components into a multipart document mobile PHP Quebec 2008 • Page 12

Slide 13: Part I Review of 14 best practices (updated) PHP Quebec 2008 • Page 13

Slide 14: Make Fewer HTTP Requests • Less components = fast page • HTTP Request overhead • Combine scripts, combine stylesheets, combine images into CSS sprites PHP Quebec 2008 • Page 14

Slide 15: CSS Sprites One request instead of ten! background-position: -0px -0px; background-position: -20px -0px; background-position: -40px -0px; background-position: -60px -0px; background-position: -80px -0px; background-position: -100px -0px; background-position: -120px -0px; background-position: -140px -0px; background-position: -160px -0px; background-position: -180px -0px; Tools: http://www.csssprites.com http://spritegen.website-performance.org/ PHP Quebec 2008 • Page 15

Slide 16: Use a Content Delivery Network • For static components • Content closer to your users • Akamai, Amazon S3 PHP Quebec 2008 • Page 16

Slide 17: Add Expires header (or Cache-control) • For static components – “Never expire” policy, far future Expires header – Once a component is served, the browser never asks for it again – When you need to change a component, rename it – Apache example: ExpiresActive On ExpiresDefault "modification plus 10 years" • For dynamic components – Use Cache-control – Help the browser send If-Modified-Since – Writeup on YUI blog/YDN coming up, stay tuned PHP Quebec 2008 • Page 17

Slide 18: Gzip Components • You send zipped content over the wire, the browser unpacks it • Modern browsers understand compressed content • Search engine spiders do too • Request header Accept-Encoding: gzip,deflate • Response header Content-Encoding: gzip • All text components should be sent gzipped: html (php), js, css, xml, txt… PHP Quebec 2008 • Page 18

Slide 19: Put CSS at the Top • Firefox and IE will not render anything before the last piece of CSS arrives over the wire • Even CSS that is not needed such as @media print • Place the stylesheets as early as possible in the document <head> <title>My page</title> <link href=“styles.css” …/> </head> <body>  PHP Quebec 2008 • Page 19

Slide 20: Move Scripts to the Bottom (inline too) • Scripts block downloads • The browser’s logic: since this script can do location.href or document.write at any time, why download possibly useless components • Move scripts to the bottom to remove the download block • Inline scripts too  <script src=“script.js” …/> </body> </html> PHP Quebec 2008 • Page 20

Slide 21: Avoid CSS Expressions • CSS expression: #content { position: absolute; left: expression(document.body.offsetWidth+‘px’); } • IE-only way to have JavaScript in CSS • They tend to get executed more often than you planned, think onmousemove often • Smart expressions overwrite themselves PHP Quebec 2008 • Page 21

Slide 22: Make JavaScript and CSS External • Helps with caching, “never expire” policy • Share with other pages • But this is two more HTTP requests • Homepages might consider inlining • yahoo.com PHP Quebec 2008 • Page 22

Slide 23: Reduce DNS Lookups • Browser needs to map domain name to an IP address • DNS lookups take time • 2-4 domains per page PHP Quebec 2008 • Page 23

Slide 24: Minify JavaScript and CSS (inline too) • Minify, but still gzip • JSMin (written in JavaScript, but has a PHP port) • YUI compressor – minifies CSS too • Inline styles and scripts should also be minified PHP Quebec 2008 • Page 24

Slide 25: Minify: before /** * The dom module provides helper methods for * manipulating Dom elements. * @module dom * */ (function() { var Y = YAHOO.util, // internal shorthand getStyle, // for load time browser branching setStyle, // ditto propertyCache = {}, // for faster hyphen converts reClassNameCache = {}, // cache regexes for className document = window.document; // cache for faster lookups YAHOO.env._id_counter = YAHOO.env._id_counter || 0; PHP Quebec 2008 • Page 25

Slide 26: Minify: after (function(){var B=YAHOO.util,K,I,J={},F={},M=window.document;YAHOO.env._i d_counter=YAHOO.env._id_counter||0; PHP Quebec 2008 • Page 26

Slide 27: Avoid Redirects • A wasted HTTP request • Causes a restart PHP Quebec 2008 • Page 27

Slide 28: Remove Duplicate Scripts • Duh! • IE might decide to download them again PHP Quebec 2008 • Page 28

Slide 29: Configure ETags • ETags are meant to help with caching • A component served from server A has a different ETag than the same component served from B • Configure ETags not to include inode • … or just remove them and implement “never expire” policy Apache default FileETag INode MTime Size Change to FileETag None PHP Quebec 2008 • Page 29

Slide 30: Make AJAX Cacheable • Content returned from XMLHttpRequests is like any other component • Should be gzipped • Could be cached • Cache-control: max-age=? PHP Quebec 2008 • Page 30

Slide 31: Part II After YSlow “A”: 20 more best practices PHP Quebec 2008 • Page 31

Slide 32: Part II tag: server tag: content tag: cookie tag: javascript tag: css tag: images tag: mobile PHP Quebec 2008 • Page 32

Slide 33: Flush the buffer early • Let the browser start fetching components while your backend is busy • PHP has the function flush() • Best for busy backends / light frontends ...  </head> <?php flush(); ?> <body> ...  • Case Study: Yahoo! Search PHP Quebec 2008 • Page 33

Slide 34: Use GET for AJAX requests • GET is for retrieving data • POST is a two-step process (send headers, send data) • GET request is one TCP packet (unless you have a lot of cookies) • Max URL length 2K (because of IE) • POST without actually posting data is like GET • Yahoo! Mail Research PHP Quebec 2008 • Page 34

Slide 36: Post-load components • Ask yourself: what's absolutely required in order to render the page initially? • The rest can wait (drag and drop, animations, hidden content, images below the fold) • JavaScript is ideal candidate for splitting • YUI Image Loader • YUI Get Utility PHP Quebec 2008 • Page 36

Slide 37: Post-load components • Case study: yahoo.com • onload.js and onload.css • Progressive enhancement PHP Quebec 2008 • Page 37

Slide 38: Preload components Preload • Items you'll need in the future • Unconditional preload (google.com loads a sprite onload) • Conditional preload (search.yahoo.com after you type in the input box) • Anticipated preload – preload in advance before launching a redesign PHP Quebec 2008 • Page 38

Slide 39: Preload components (contd.) • Unconditional preload example PHP Quebec 2008 • Page 39

Slide 40: Preload components (contd.) • Conditional preload example – search.yahoo.com • When you start typing the page can safely assume you’ll hit the search results page • Time to preload PHP Quebec 2008 • Page 40

Slide 41: Reduce the number of DOM elements • World's fastest page? about:blank! • A complex page means more bytes to download • It also means slower DOM access in JavaScript • It also may mean using semantically incorrect markup (like nested tables or abusing <div>s) • Use semantic markup • Use YUI's reset.css, fonts.css, grids.css • Easy to test, just type in Firebug’s console: document.getElementsByTagName('*').length • yahoo.com is a busy page and still under 700 elements (HTML tags) PHP Quebec 2008 • Page 41

Slide 42: Split components across domains • Maximize parallel downloads • But not more than 2-4 domains, because of the DNS lookup penalty • www.example.org – HTML content • static.example.org – Static components • Future: IE8 will allow 6 requests per domain PHP Quebec 2008 • Page 42

Slide 43: Split components (contd.) 2 components in parallel 8 components in parallel PHP Quebec 2008 • Page 43

Slide 44: Minimize the number of iframes • <iframe> pros: – Can help with slow third-party content like badges and ads – Security sandbox – You can download scripts in parallel • <iframe> cons: – They have a cost even if blank – They block page onload – Non-semantic PHP Quebec 2008 • Page 44

Slide 45: No 404s • 404 Not Found • Useless downloads • Some sites have helpful 404s “Did you mean X?”… • … which uses server resources (DB, etc) • When an external JavaScript is a 404, the browser will still try to parse it and find something usable in it PHP Quebec 2008 • Page 45

Slide 46: No 404s (contd.) The second component is a 404 JavaScript and it blocks the rest of the page PHP Quebec 2008 • Page 46

Slide 48: Reduce cookie size • Eliminate unnecessary cookies • Keep cookie sizes as low as possible to minimize the impact on the user response time • Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected • Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time PHP Quebec 2008 • Page 48

Slide 49: Cookie-free hosting for components • Option 1: Separate subdomain (static.example.org) • Option 2: A new TLD (e.g. yimg.com, ytimg.com, images-amazon.com) • Proxies might refuse to cache • www.www-yes.org vs www-no.org? • no-www leaves you no choice but to write cookies to *.example.org PHP Quebec 2008 • Page 49

Slide 51: Minimize DOM access • DOM access is the slowest • Cache • Update nodes “offline” and then add them to the tree • Avoid fixing layout with JavaScript PHP Quebec 2008 • Page 51

Slide 52: Develop smart event handlers • Don't wait for onload, use DOMContentLoaded • Events bubble up, so use delegation (attach listeners to outer elements) • Clean up to prevent IE memory leaks • Careful with onresize • Use YUI Event utility PHP Quebec 2008 • Page 52

Slide 54: Choose <link> over @import • CSS should be at the top • In IE @import is the same as putting <link> at the bottom PHP Quebec 2008 • Page 54

Slide 55: Avoid filters • IE proprietary • AlphaImageLoader • Fixes an IE6 problem with semi-transparent PNGs, IE7 is fine • Blocks rendering, freezes the browser • Increased memory consumption • Per element, not per image! Best: Avoid completely, use gracefully degrading PNG8 Fallback: use underscore hack _filter not to penalize IE7+ users PHP Quebec 2008 • Page 55

Slide 57: Optimize images • GIF - don't use a bigger palette than you need • Use PNGs instead of GIFs • “All we are saying is: Give PiNG a Chance!" • pngcrush tool (or optipng, or pngoptimizer) • Removing gamma chunks also helps with cross- browser colors • Strip comments • jpegtran - lossless JPEG operations, can be used to optimize and remove comments PHP Quebec 2008 • Page 57

Slide 58: Optimize images (contd.) You can write a simple tool that walks your image directories before site launch and does the following: 1. Convert all GIFs to PNGs (and check if there’s a saving) > convert image.gif image.png 2. Crush all PNGs > pngcrush image.png –rem alla –reduce result.png 3. Strip comments from JPEGs > jpegtran -copy none -optimize -perfect src.jpg dest.jpg PHP Quebec 2008 • Page 58

Slide 59: Optimize images (contd.) • You’d be surprised how many sites, from small to huge, could optimize the download size • 200K of useless image information sent over the wire for a single page?! PHP Quebec 2008 • Page 59

Slide 60: Optimize CSS sprites • Choose horizontal over vertical when possible • Combine similar colors • Keep color count low (<256) to fit in a PNG8 • “Be mobile-friendly” – don’t leave big gaps – Filesize doesn’t increase much, but the image needs to be decompressed into a pixel map – 100x100 is 10000 pixels – 1000x1000 is 1 Million pixels – Case study: Yahoo! Mail Classic PHP Quebec 2008 • Page 60

Slide 61: Optimize sprites PHP Quebec 2008 • Page 61

Slide 62: Don't scale images in HTML • Downloads unnecessary bytes • If you need <img width="100" height="100" src="mycat.jpg" /> then have mycat.jpg 100x100 not 500x500 PHP Quebec 2008 • Page 62

Slide 63: Make favicon.ico small and cacheable • www.example.org/favicon.ico • Necessary evil: – The browser will request it – Better not respond with a 404 – Cookies are sent – Cannot be on CDN – Interferes with the download sequence • Make it small (<= 1K) • Animated favicons are not cool • Set Expires header • Tools: imagemagick, png2ico • Case study: Yahoo! Search - favicon.ico is 9% of all page views! PHP Quebec 2008 • Page 63

Slide 64: Bonus: crossdomain.xml • Cross domain policy for Flash/Flex • Sits in the root: example.org/crossdomain.xml <cross-domain-policy> <allow-access-from domain="*.yahoo.com" secure="false"/> </cross-domain-policy> • Set Expires header • gzip • … and secure while at it, don’t do: <allow-access-from domain="*“ /> PHP Quebec 2008 • Page 64

Slide 66: Keep components under 25K • Because iPhone won’t cache them • Uncompressed size under 25Kb • Minify HTML in addition to JS and CSS PHP Quebec 2008 • Page 66

Slide 67: Pack components into a multipart document • For UAs that support it (iPhone doesn’t) • Like an email with attachments PHP Quebec 2008 • Page 67

Slide 69: Tools • YSlow (http://developer.yahoo.com/yslow/) • Fiddler (http://www.fiddlertool.com/fiddler/) • IBM Page Detailer (http:// www.alphaworks.ibm.com/tech/pagedetailer) • HTTPWatch (http://www.httpwatch.com/) • AOL Pagetest (http://pagetest.wiki.sourceforge.net/) • Firebug Net Panel (http://www.getfirebug.com/) PHP Quebec 2008 • Page 69

Slide 70: IBM Page Detailer • Methodology – Packet Sniffer • Competitive Advantage – Most accurate – Provides detailed data – Works for any browser – Best waterfall view • Drawbacks – Requires a download – 90 day free trial – Runs only on Windows – Misses cached components PHP Quebec 2008 • Page 70

Slide 71: Firebug NET Panel • Methodology – Packet Sniffer • Competitive Advantage – Integrated with Firebug – Displays waterfall view – Provides HTTP header info • Drawbacks – Runs only in Firefox – Inaccurate waterfall view • No render time • No parse time • No redirects • No DNS lookups – Misses cached components PHP Quebec 2008 • Page 71

Slide 72: URLs – Exceptional Performance YUI blog http://yuiblog.com/blog/category/performance/ YDN (Yahoo Developer Network) http://developer.yahoo.com/performance/ YDN blog http://developer.yahoo.net/blog/archives/performance/ Mailing list (Yahoo! Group) http://tech.groups.yahoo.com/group/exceptional-performance/ Feedback http://developer.yahoo.com/yslow/feedback.html PHP Quebec 2008 • Page 72

Slide 73: URLs (contd.) • "When the Cookie Crumbles" Tenni Theurer, Steve Souders http://yuiblog.com/blog/2007/03/01/performance-research-part-3/ • "Maximizing Parallel Downloads in the Carpool Lane", Tenni Theurer, Patty Chi http://yuiblog.com/blog/2007/04/11/performance-research-part-4/ • YUI Image Loader (http://developer.yahoo.com/yui/imageloader/) • YUI Get (http://developer.yahoo.com/yui/get/) • YUI Compressor (http://developer.yahoo.com/yui/compressor/ contains a Java port of an internal PHP CSS minifier tool written by Isaac Schlueter, http://foohack.com/) • JSMin (http://www.crockford.com/javascript/jsmin.html) • "High-performance AJAX applications" Julien Lecompte http://yuiblog.com/blog/2007/12/20/video-lecomte/ • Yahoo! engineer Michael J. Radwin talk back in 2004 http://www.radwin.org/michael/talks/ PHP Quebec 2008 • Page 73

Slide 74: Credits – thank you! PHP Quebec 2008 • Page 74

Slide 75: Take-home • Focus on the front-end • Harvest the low hanging fruit • Be an advocate for your users • Start early PHP Quebec 2008 • Page 75

Slide 76: Thank you! Merci beaucoup! PHP Quebec 2008 • Page 76

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