Transcript High Performance Web Sites 14 rules for faster

Even Faster Websites
Steve Souders
[email protected]
http://stevesouders.com/docs/cbs-20090209.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://en.oreilly.com/velocity2009
June 22-24, 2009
Even Faster Websites
1.
2.
3.
4.
5.
6.
7.
8.
Split the initial payload
Load scripts without blocking
Don't scatter inline scripts
Couple asynchronous scripts
Split dominant domains
Simplify CSS Selectors
Use iframes sparingly
Flush the document early
O'Reilly, Q2 2009
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 13K+ tests, 9K+ unique testers, 50+
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
CNet Performance Analysis
cool
– flushed document
– HTTP/1.0 downgrade
requests: 107
load time: 3.7 secs
xfer size: 436K
YSlow: F (48)
opportunities
–
–
–
–
–
–
load oreo.moo.rb.combined.js async
split i.i.com.com across two domains
concatenate 10 scripts
sprite 25 CSS background images
30 resources with short Expires
62% (62K) of CSS not used
BNet Performance Analysis
cool
– flushed document
– @import stylesheets
requests: 149
load time: 5.9 secs
xfer size: 759K
YSlow: F (26)
opportunities
–
–
–
–
–
–
–
compress 235K (16 files)
sprite 57 CSS background images
concatenate 12 scripts, 6 stylesheets
optimize images (30K, 16%)
106 resources with short Expires
60% (29K) of CSS not used
remove ETags
CBSSports Performance Analysis
cool
– flushed document
opportunities
–
–
–
–
–
–
–
–
–
–
–
requests: 99
load time: 8.2 secs
xfer size: 689K
YSlow: F (31)
compress 151K (11 files)
move inline script above stylesheets
concatenate 16 scripts
sprite 26 CSS background images
optimize images (104K, 28%)
move www.cbssports.com images to a CDN
split images.cbssports.com across two domains
almost all resources have a short Expires
49% (24K) of CSS not used
minify 63K (8 scripts)
remove ETags
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
Impact on Revenue
Google: +500 ms  -20% traffic1
Yahoo: +400 ms  -5-9% full-page traffic
Amazon: +100 ms  -1% sales1
http://home.blarg.net/~glinden/StanfordDataMining.2006-11-29.ppt
2 http://www.slideshare.net/stoyan/yslow-20-presentation
1
2
Cost Savings
hardware – reduced load
bandwidth – reduced response size
http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf
if you want
better user experience
more revenue
reduced operating expenses
the strategy is clear
Even Faster Websites
Steve Souders
[email protected]
http://stevesouders.com/docs/cbs-20090209.ppt