php quebec 2008 page 1 high performance web pages stoyan stefanov yahoo! exceptional performance ...

PHP Quebec 2008 •

High PerformanceWeb Pages

Stoyan StefanovYahoo! Exceptional Performancehttp://developer.yahoo.com/performancePHP Quebec, March 13, 2008

PHP Quebec 2008 •

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 •

This talk• How to improve page performance• Focus on the front-end• 14 best practices for faster pages• … and 20 more!

PHP Quebec 2008 •

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 •

Back-

end=5%

Front-

end=95

%Even here, front-end=88%

The Importance of Front-End Performance

PHP Quebec 2008 •

Focus on the front-end

• 80-90% of the time• Easier than the back-end• Proven to work

PHP Quebec 2008 •

List of 14 best practices (updated)1. Make Fewer HTTP Requests2. Use a Content Delivery Network3. Add Expires header (or Cache-control)4. Gzip Components5. Put CSS at the Top6. Move Scripts to the Bottom (inline too)7. Avoid CSS Expressions8. Make JavaScript and CSS External9. Reduce DNS Lookups10.Minify JavaScript and CSS (inline too)11.Avoid Redirects12.Remove Duplicate Scripts13.Configure ETags14.Make AJAX Cacheable

http://developer.yahoo.com/performance/rules.html

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http://developer.yahoo.com/performance/rules.html

PHP Quebec 2008 •

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 •

PHP Quebec 2008 •

The Life of Page 2.0

request HTML sent onload

page settles

conception birth graduation marriage? R.I.P.

User perceived “onload” happens somewhere here

user interaction, XHRsevent handlers, components, XHRs

request

backend fetching components

fetuschildteenadult

PHP Quebec 2008 •

After YSlow "A"?1. Flush the buffer early2. Use GET for AJAX requests3. Post-load components4. Preload components5. Reduce the number of DOM elements6. Split components across domains7. Minimize the number of iframes8. No 404s9. Reduce cookie size10. Use cookie-free domains for components11. Minimize DOM access12. Develop smart event handlers 13. Choose <link> over @import14. Avoid filters15. Optimize images16. Optimize CSS sprites17. Don't scale images in HTML18. Make favicon.ico small and cacheable19. Keep components under 25K20. Pack components into a multipart document

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PHP Quebec 2008 •

Part I

Review of 14 best practices (updated)

PHP Quebec 2008 •

Make Fewer HTTP Requests• Less components =

fast page• HTTP Request

overhead• Combine scripts,

combine stylesheets, combine images into CSS sprites

PHP Quebec 2008 •

CSS Sprites

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;

One request instead of ten!

Tools:http://www.csssprites.comhttp://spritegen.website-performance.org/

http://www.csssprites.com/

http://spritegen.website-performance.org/

PHP Quebec 2008 •

Use a Content Delivery Network• For static components• Content closer to your users• Akamai, Amazon S3

PHP Quebec 2008 •

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 •

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 •

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 •

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 •

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 •

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 •

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 •

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 •

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 •

Minify: after(function(){var B=YAHOO.util,K,I,J={},F={},M=window.document;YAHOO.env._id_counter=YAHOO.env._id_counter||0;

PHP Quebec 2008 •

Avoid Redirects• A wasted HTTP request• Causes a restart

PHP Quebec 2008 •

Remove Duplicate Scripts• Duh!• IE might decide to download them again

PHP Quebec 2008 •

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 •

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 •

Part II

After YSlow “A”:20 more best practices

PHP Quebec 2008 •

Part II

tag: servertag: contenttag: cookie tag: javascript tag: css tag: images tag: mobile

PHP Quebec 2008 •

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 •

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 •

Part II


PHP Quebec 2008 •

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 •

Post-load components• Case study: yahoo.com• onload.js and onload.css• Progressive enhancement

PHP Quebec 2008 •

Preload componentsPreload• 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 •

Preload components (contd.)• Unconditional preload example

PHP Quebec 2008 •

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 •

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 •

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 •

Split components (contd.)

2 components in parallel 8 components in parallel

PHP Quebec 2008 •

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 •

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 •

No 404s (contd.)

The second component is a 404 JavaScript and it blocks the rest of the page

PHP Quebec 2008 •

Part II


PHP Quebec 2008 •

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 •

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 •

Part II


PHP Quebec 2008 •

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 •

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 •

Part II


PHP Quebec 2008 •

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 •

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 •

Part II


PHP Quebec 2008 •

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 •

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 •

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 •

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 •

Optimize sprites

PHP Quebec 2008 •

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 •

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 •

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 •

Part II


PHP Quebec 2008 •

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 •

Pack components into a multipart document• For UAs that support it (iPhone doesn’t)• Like an email with attachments

PHP Quebec 2008 •

Part II


PHP Quebec 2008 •

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/)




http://www.fiddlertool.com/fiddler/



http://www.alphaworks.ibm.com/tech/pagedetailer

http://www.alphaworks.ibm.com/tech/pagedetailer

http://www.httpwatch.com/



http://pagetest.wiki.sourceforge.net/



http://www.getfirebug.com/



PHP Quebec 2008 •

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 •

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 •

URLs – Exceptional PerformanceYUI 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/

Feedbackhttp://developer.yahoo.com/yslow/feedback.html

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

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

http://developer.yahoo.net/blog/archives/performance/



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

PHP Quebec 2008 •

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 Chihttp://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/

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

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

http://developer.yahoo.com/yui/imageloader/



http://developer.yahoo.com/yui/get/

http://developer.yahoo.com/yui/compressor/



http://foohack.com/

http://www.crockford.com/javascript/jsmin.html

http://www.crockford.com/javascript/jsmin.html

http://yuiblog.com/blog/2007/12/20/video-lecomte/




PHP Quebec 2008 •

Credits – thank you!

PHP Quebec 2008 •

Take-home• Focus on the front-end• Harvest the low hanging fruit• Be an advocate for your users• Start early

PHP Quebec 2008 •

Thank you!Merci beaucoup!

php quebec 2008 page 1 high performance web pages stoyan stefanov yahoo! exceptional performance ...

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