The document discusses best practices for optimizing website performance, emphasizing the importance of front-end improvements like reducing response times and HTTP requests. It details various strategies such as compression, minification of static content, combining resources, and using CDNs to enhance user experience and increase revenue. Tools and examples from Xero’s experience illustrate the effectiveness of these optimization techniques.

1. Building Faster Websites
Craig Walker, Chief Technology Officer

2. What is Xero?
http://www.xero.com/signup/

3. Performance === Usability

4. Performance === Money
• Bing: +2s in response time = 4.3% LOSS
of revenue/user
• Google: +500ms in response time = 20%
LESS traffic
• Amazon: +100ms in response time = 1%
LESS sales
• Shopzilla: +5s response time led to 12%
increase in revenue & 25% increase in
page views

6. Receive
Last Byte
Send
Last Byte
Send Data
The HTTP Request
Server
Browser
Establish
Connection
Initial
Connection
Open Socket
Initial HTTP
Request
First Byte
Receive
First Byte
Send
First Byte
Content Download
ISP
Get IP
DNS
Lookup

7. 5%
95%

8. 25%
75%

9. Empty Cache Primed Cache

10. Focus on the front-end
• 75-95% of the end-user response time for
Xero customers was spent on the front
end
• Much easier to optimise than server side
performance
• Greater potential for improvement –
especially from a front-end users point of
view

11. • MySpace's Performance
Tracker
msfast.myspace.com
• MS Visual Round Trip
Analyzer
Lotsa tools!
• HTTPWatch
www.httpwatch.com
• AOL PageTest
www.webpagetest.org

12. The ones we use at Xero …
• Fiddler
www.fiddlertool.com
• Firebug
www.getfirebug.com
• YSlow
developer.yahoo.com/ysl
ow

13. We don't all run Windows 7 & IE8 …
6616
29275
15596
5318
27233
Browsers
Chrome IE7 IE8
Safari 4 Firefox 3
728
10891
20717
53065
1383
Operating Systems
Linux MacOSX
Vista XP
Windows 7

14. Fiddler

15. The Rules

16. Zip It!
• Significantly reduces download
size – 60-80% saving on text
based content
• 90% of browsers support
compression
• Benefits users & you too:
– Reduces traffic costs
– Doesn’t require code change
• Zip everything you can
– html, aspx, js, css, xml, txt, json,
ashx …

17. Fly’s down Zipped

18. Turning on HTTP
Compression

19. Things to be wary of with compression
…
• Make sure you test – don't assume compression
• Approximately 5% of users get uncompressed
responses
• Browsers (& other applications) indicate compression
support by sending Accept-Encoding: gzip,
deflate and responding with Content-Encoding:
gzip
• Some client software (anti-virus, anti-phishing) and
proxy servers can strip Accept-Encoding
• If Accept-Encoding is missing let your users know!
• Use Advanced Logging for IIS7 to track request &
response headers
http://www.iis.net/extensions/advancedlogging

20. Minify all static content
• CSS, JavaScript, XML, JSON, HTML can all be
minified
• Not a replacement for gzipping but is a perfect
accompaniment to it (we've seen up to 50% extra
savings)
• No shortage of tools:
– JSMin
– CSSTidy
– YUI Compressor
• JavaScript obfuscation can also be useful – just test
that your app still works afterwards

21. You don't really want people to read your code do
you?
Ext.DomHelper = function(){
var tempTableEl = null;
var emptyTags =
/^(?:br|frame|hr|img|input|link|meta|range|spacer|wbr|ar
ea|param|col)$/i;
var tableRe = /^table|tbody|tr|td$/i;
var createHtml = function(o){
if(typeof o == 'string'){
return o;
}
var b = "";
if (Ext.isArray(o)) {
for (var i = 0, l = o.length; i < l; i++) {
b += createHtml(o[i]);
}
return b;
}
if(!o.tag){
o.tag = "div";
}
b += "<" + o.tag;
for(var attr in o){
if(attr == "tag" || attr == "children" ||
attr == "cn" || attr == "html" || typeof o[attr] ==
"function") continue;
if(attr == "style"){
var s = o["style"];
if(typeof s == "function"){
s = s.call();
}
if(typeof s == "string"){
b += ' style="' + s + '"';
}else if(typeof s == "object"){
Ext.DomHelper=function(){var n=null;var
g=/^(?:br|frame|hr|img|input|link|meta|range|spacer|wbr|area|param|co
l)$/i;var b=/^table|tbody|tr|td$/i;var a=function(w){if(typeof
w=="string"){return w;}var q="";if(Ext.isArray(w)){for(var
u=0,r=w.length;u<r;u++){q+=a(w[u]);}return
q;}if(!w.tag){w.tag="div";}q+="<"+w.tag;for(var p in
w){if(p=="tag"||p=="children"||p=="cn"||p=="html"||typeof
w[p]=="function"){continue;}if(p=="style"){var v=w["style"];if(typeof
v=="function"){v=v.call();}if(typeof v=="string"){q+='
style="'+v+'"';}else{if(typeof v=="object"){q+=' style="';for(var t
in v){if(typeof
v[t]!="function"){q+=t+":"+v[t]+";";}}q+='"';}}}else{if(p=="cls"){q+=
' class="'+w["cls"]+'"';}else{if(p=="htmlFor"){q+='
for="'+w["htmlFor"]+'"';}else{q+="
"+p+'="'+w[p]+'"';}}}}if(g.test(w.tag)){q+="/>";}else{q+=">";var
x=w.children||w.cn;if(x){q+=a(x);}else{if(w.html){q+=w.html;}}q+="</"
+w.tag+">";}return q;};var o=function(v,q){var
u;if(Ext.isArray(v)){u=document.createDocumentFragment();for(var
t=0,r=v.length;t<r;t++){o(v[t],u);}}else{if(typeof
v=="string"){u=document.createTextNode(v);}else{u=document.createElem
ent(v.tag||"div");var s=!!u.setAttribute;for(var p in
v){if(p=="tag"||p=="children"||p=="cn"||p=="html"||p=="style"||typeof
v[p]=="function"){continue;}if(p=="cls"){u.className=v["cls"];}else{i
f(s){u.setAttribute(p,v[p]);}else{u[p]=v[p];}}}Ext.DomHelper.applySty
les(u,v.style);var
w=v.children||v.cn;if(w){o(w,u);}else{if(v.html){u.innerHTML=v.html;}
}}}if(q){q.appendChild(u);}return u;};var
k=function(v,t,r,u){n.innerHTML=[t,r,u].join("");var p=-
1,q=n;while(++p<v){q=q.firstChild;}return q;};var
l="<table>",e="</table>",c=l+"<tbody>",m="</tbody>"+e,i=c+"<tr>",d="<
/tr>"+m;var
h=function(p,q,s,r){if(!n){n=document.createElement("div");}var t;var
u=null;if(p=="td"){if(q=="afterbegin"||q=="beforeend"){return;}if(q==
"beforebegin"){u=s;s=s.parentNode;}else{u=s.nextSibling;s=s.parentNod
e;}t=k(4,i,r,d);}else{if(p=="tr"){if(q=="beforebegin"){u=s;s=s.parent
Node;t=k(3,c,r,m);}else{if(q=="afterend"){u=s.nextSibling;s=s.parentN
ode;t=k(3,c,r,m);}else{if(q=="afterbegin"){u=s.firstChild;}t=k(4,i,r,
d);}}}else{if(p=="tbody"){if(q=="beforebegin"){u=s;s=s.parentNode;t=k
(2,l,r,e);}else{if(q=="afterend"){u=s.nextSibling;s=s.parentNode;t=k(
2,l,r,e);}else{if(q=="afterbegin"){u=s.firstChild;}t=k(3,c,r,m);}}}el
se{if(q=="beforebegin"||q=="afterend"){return;}if(q=="afterbegin"){u=
s.firstChild;}t=k(2,l,r,e);}}}s.insertBefore(t,u);return
955KB -> 265KB 539KB -> 141KB

22. Reduce HTTP Requests
• Less components means a
faster page
• Every request is an overhead
• Combine scripts
• Combine CSS
• Combine images into CSS
Sprites
• Don’t rely on cache: 304’s are
still requests

23. CSS Sprites
• Combine all small images
into one large image
• Use CSS to control the
displaying of each image

24. The designers want what?
11 images
11 HTTP Requests
3.3 KB total size

25. Obey your thirst®
1 image
1 HTTP Request
1.6 KB total size

26. And the code?
<div class="buttons">
<span class="large green button">
<button type="button">
<span class="checkbox icon">
Approve
</span>
</button>
</span>
<span class="large blue button">
<button type="button">
<span>
Save
</span>
</button>
</span>
<span class="large red button">
<button type="button">
<span class="delete icon">
Delete
</span>
</button>
</span>
<span class="medium gray button">
<button type="button">
<span class="delete icon">
Cancel
</span>
</button>
</span>
</div>
.buttons span.button {
background:transparent url(buttons.png) no-repeat 0 0;
}
.buttons span.button button, .buttons span.button a {
background:transparent url(buttons.png) no-repeat 100% -120px;
}
.buttons span.blue {
background-position: 0 -30px;
}
.buttons span.blue button, .buttons span.blue a {
background-position: 100% -150px;
}
.buttons span.red {
background-position: 0 -60px;
}
.buttons span.red button, .buttons span.red a {
background-position: 100% -180px;
}
.buttons span.green {
background-position: 0 -90px;
}
.buttons span.green button, .buttons span.green a {
background-position: 100% -210px;
}

27. SpriteMe

28. Optimise images
• Use PNGs instead of GIFs
• Avoid alpha filters – can block rendering and
freeze the browser
• PNG8 is best and supported by IE6 (yes – even
with transparency
• Optimise further with tools like PNGOUT
• Make sure you have a favicon.ico:
• Every browser will request it
• Best not to respond with a 404
• Make it small and cacheable

29. 12KB15KB

30. Maximise Parallel Downloads
• Most browsers are limited to 6 connections total and 2
connections per hostname
Browser Parallel Downloads
Firefox 3.x 6
Internet Explorer 7 2
Internet Explorer 8 6
Safari 3.x 4
Safari 4 4
Chrome 4
• Increase the number of hostnames to increase the number
of parallel downloads
• Don't overdo it! (DNS lookups are expensive so limit to 2-4
domains)

33. JavaScript external and on the bottom
• Move scripts to external files for both reuse and caching
• Promotes better script design
• Push scripts as low as possible
– Often difficult with document.write or with inline calls requiring
loaded JavaScript
– Be pragmatic – think about splitting JavaScript into “must be
loaded” and “can be loaded on demand”
• Scripts will block both downloading and rendering until
parsed
• Remove duplicate scripts (IE has a habit of downloading
them again)

34. Maximise the cache
• Understand the ratio of users with cached vs uncached
• Add an Expires header
– Not just for images – should be used on all static content
– Set a “Never expire” or far future expires policy if you can
– Reduces HTTP requests – once component is served, the
browser never asks for it again
– Date stamping in file names makes it easier
• Remove ETags
– ETags are another caching mechanism – sent with every request
– Uniquely created per web server – not good in web farms
– Just turn them off and use Expires headers instead

35. Use a CDN
• Content Delivery Network
• Distributes content closer to the last mile
• Distribute your static content before distributing your
dynamic content
• Akamai most popular but expensive for small sites
• Xero utilises a rudimentary CDN using IP lookup to
determine location

36. GET
Request
Response with
HTML document
Images
JS
CSS
How it works:
RegisterCSS("/common/style/xero.css", "screen")
RegisterJavascript("/common/scripts/xero.js")
<link rel="stylesheet" type="text/css" media="screen"
href="https://nzs1.xero.com/common/style/xero.css" />
<script type="text/javascript"
src="https://nzs2.xero.com/common/scripts/xero.js">
</script>
Get
location
from IP

37. Reduce cookie weight
• Cookies are sent back with
every request
• Keep cookie size small and
only store what's required –
use server-side storage for
everything else
• Consider cookie free domains
for static content
• And while we're at it – reduce
ViewState too!

38. Preloading …
• Preload components
you’ll need in the future
• Unconditional preload
– Xero login page preloads
all core components so that
the dashboard experience
is better
• Conditional preload
– Often based on where you
think a user might go to
next

39. YSlow
• Firebug extension
• Grades performance – not about
response times but about how
well a site has adopted the
techniques suggested
• Response time inversely
proportional to YSlow score –
get as close to A as possible to
get the maximum performance
gain

40. YSlow

41. Aptimize
• Plugin that works with both IIS &
Apache
• Merges CSS & JSS files
• Reduces & optimises images with
CSS sprites & CSS inlining
• Compresses content with
minification
• Improves caching
• Used by over 300 websites &
intranets
• And it does all this in real-time!
www.aptimize.com

42. Aptimize

43. Aptimizing Microsoft
• Microsoft used Aptimize to
speed up
sharepoint.microsoft.com
• HTTP requests reduced
from 96 to 35
• Sped up first view, repeat
view and start render by
over 50%
• YSlow went from an E to a
B

44. Things to take away
• Focus on the front-end
• Be an advocate for your users – isn't it nice to
have happy users?
• Faster web sites lead to:
– Better user experience
– Reduced operating expenses
– Increase revenue

46. www.xero.com