Transcript High Performance Web Sites 14 rules for faster

Life's too short,
write fast code
part 1
Steve Souders
[email protected]
http://stevesouders.com/docs/myspace-20081024.ppt
Disclaimer: This content does not necessarily reflect the opinions of my employer.
The Importance of Frontend
Performance
9%
17%
91%
83%
iGoogle, primed cache
iGoogle, empty cache
Time Spent on the Frontend
www.aol.com
www.ebay.com
www.facebook.com
www.google.com/search
search.live.com/results
www.msn.com
www.myspace.com
en.wikipedia.org/wiki
www.yahoo.com
www.youtube.com
Empty Cache
97%
Primed Cache
97%
95%
95%
47%
81%
81%
0%
67%
98%
98%
94%
0%
94%
98%
91%
97%
98%
96%
97%
April 2008
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
14 Rules
1. Make fewer HTTP requests
2. Use a CDN
3. Add an Expires header
4. Gzip components
5. Put stylesheets at the top
6. Put scripts at the bottom
7. Avoid CSS expressions
8. Make JS and CSS external
9. Reduce DNS lookups
10. Minify JS
11. Avoid redirects
12. Remove duplicate scripts
13. Configure ETags
14. Make AJAX cacheable
YSlow
High Performance Web Sites
http://conferences.oreilly.com/velocity/
June 22-24, 2009
High Performance Web Sites, Vol 2
}
1. Split the initial payload
2. Load scripts without blocking part 1
3. Don't scatter inline scripts
4. Split dominant domains
5. Make static content cookie-free
6. Reduce cookie weight
7. Minify CSS
8. Optimize images
9. Use iframes sparingly
10.To www or not to www
Why focus on JavaScript?
Yahoo!
Wikipedia
eBay
AOL
MySpace
YouTube
Facebook
Scripts Block
<script src="A.js"> blocks parallel
downloads and rendering
http://stevesouders.com/cuzillion/?ex=10008
What's "Cuzillion"?
Initial Payload and Execution
JavaScript
Functions Executed
before onload
www.aol.com
www.ebay.com
www.facebook.com
www.google.com/search
115K
183K
1088K
15K
30%
44%
9%
45%
search.live.com/results
www.msn.com
www.myspace.com
en.wikipedia.org/wiki
17K
131K
297K
114K
24%
31%
18%
32%
www.yahoo.com
www.youtube.com
321K
240K 252K avg
13%
18% 26% avg
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?
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)
Advanced Script Loading
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
XHR Eval
var xhrObj = 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
XHR Injection
var xhrObj = 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
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
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
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
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
Browser Busy Indicators
Browser Busy Indicators
normal Script Src
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write
Script Tag
status
bar
progress
bar
logo
cursor
block
render
block
onload
FF
IE,FF
IE,FF
FF
IE,FF
IE,FF
no
no
no
no
no
no
no
no
no
no
no
no
IE,FF
FF
IE,FF
FF
no
IE,FF
FF
FF
FF
FF
no
FF
FF
FF
FF
FF
FF
IE,FF
FF
IE,FF
IE,FF
FF
IE,FF
IE,FF
good to show busy indicators when the user needs feedback
bad when downloading in the background
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
Summary of Traits
||
domains
existing browser ensures
downcan
scripts
busy
order
loads
differ
normal Script Src
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write
Script Tag
*Only
size
(bytes)
no
yes
yes
IE,FF
IE,FF
~50
IE,FF
no
no
no
no
~500
IE,FF
no
yes
no
no
~500
IE,FF
no
no
IE,FF
no
~50
IE,FF
yes
yes
FF
FF
~200
IE
yes
yes
IE,FF
IE
~50
IE*
yes
yes
IE,FF
IE
~100
other document.write scripts are downloaded in parallel (in the same script block).
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
no order
preserve order
XHR Eval
XHR Injection
Script in iframe
Script DOM Element (IE)
preserve order
Script DOM Element (FF)
Script Defer (IE)
Managed XHR Eval
Managed XHR Injection
Script DOM Element
no busy
Script DOM Element (FF)
Script Defer (IE)
Managed XHR Injection
Managed XHR Eval
no busy
XHR Injection
XHR Eval
Script DOM Element (IE)
show busy
Managed XHR Injection
Managed XHR Eval
Script DOM Element
show busy
Script DOM Element (FF)
Script Defer (IE)
Managed XHR Eval
Managed XHR Injection
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?
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
Examples of Scattered Scripts
MSN
Wikipedia
eBay
MySpace
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
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 2K+ tests, 1K+ unique testers, 100+
browsers
help out by running the test!
Measuring Performance
Episodes
dev box
Hammerhead
synthetic
testing
bucket
testing
real user
data
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
Splash
YSlow: 74
unused JS: ~87%
unused CSS: ~61%, 47K
Home
YSlow: 49
unused JS: ~86%
unused CSS: ~61%, 44K
Profile
YSlow: 81
unused JS: ~91%
unused CSS: ~69%, 43K
Splash
YSlow: 60
unused JS: ~89%
unused CSS: ~65%, 36K
MySpace performance analysis
analyzed Splash, Home, Profile, More Pics
the good
•
•
•
•
•
•
future Expires (10 days)
gzip
some CSS sprites
no CSS expressions
no redirects
bad ETags syntax changed
MySpace performance analysis
the opportunities
• YSlow: 74, 49, 81 60
added myspacecdn.com, x.myspace.com to CDN list
•
•
•
•
•
ads
combine scripts & stylesheets
split JS payload: ~90% unused (~360K uncomp)
remove unused CSS: ~65% (~50K uncomp)
move scripts to the bottom or load w/o
blocking
• minify scripts
HTTP waterfall
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
life's too short, write fast code
Steve Souders
[email protected]
http://stevesouders.com/docs/myspace-20081024.ppt