3. “Has it loaded yet?”
http://www.flickr.com/photos/kindofindie/4099768084
4. Our perception of response time
Instant
Seamless Yawn!
100ms 1s 10s
3s - Recommended 6.5s - Alexa 2000
Load Time Fall 2012
Response Time in Man-computer Conversational Transactions
Robert B. Miller, 1968
5. “50% more concentration when using
badly performing web sites”
Foviance
http://www.flickr.com/photos/yourdon/3366991042
6. Effect of delay on abandonment rate...
Abandonment rate over 200+ sites / 177+ million page views over 2 weeks - http://www.measureworks.nl / Gomez
22. Over 80% of page load time is on front-end
Backend
news.bbc.co.uk
Frontend
ebay.co.uk
debenhams.co.uk
direct.gov.uk
amazon.co.uk
mumsnet.com
guardian.co.uk
0 1 2 3 4 5
Measured via residential ADSL line using Google Chrome
24. Bandwidth (often) isn’t the bottleneck
2.0
1.5
1.0
0.5
0s 5s 10s
news.bbc.co.uk tested via webpagetest.org throttled at 1.5Mbps
(bursts over 1.5Mbps are artefact of testing)
26. Visualising TCP
Carlos Bueno (@archivd) https://vimeo.com/14439742
27. Impact of Latency
4
3
Page Load Time (s)
2
1
0 20 40 60 80 100 120 140 160 180 200 220 240
Round Trip Time (ms)
28. Minimum round trips to download a file
(TCP Segments)
285kB
214kB
143kB
71kB
Size
1 2 3 4 5 6 7 8 9 10 11
Round Trips TCP and the Lower Bound of Web Performance
John Rauser
29. Latency is Our Biggest Enemy
“In 2012, the average worldwide RTT to Google is still
~100ms, and ~50-60ms within the US.”
“we are looking at 100-1000ms RTT range on mobile”
Ilya Grigorik
http://www.igvita.com/2012/07/19/latency-the-new-web-performance-bottleneck/
30. 3G Radio Resource Control
Idle for 12s
IDLE CELL_FACH
1s delay
1-2s delay!
CELL_DCH Idle for 5s
Exact timings vary and depend on carrier NOT device
http://web.eecs.umich.edu/~fengqian/paper/3g_imc10.pdf
39. Use “Right-sized” Images
http://www.flickr.com/photos/emzee/139794246
Standards support (picture? srcset?) is coming but unclear when!
Meanwhile services such as sencha.io, resrc.it and JS libraries -
picturefill.js, foresight.js can help.
41. Parallel Downloads
news.bbcimg.co.uk
static.bbc.co.uk
Domain Sharding increases number of parallel downloads but…
…more connections may not be a good idea on mobile
…may also interfere with multiplexing in protocols like SPDY
42. Get the <head> straight
<!doctype html>
<html>
<head>
CSS before JS
<meta charset="utf-8"> Ideally one file*
<title>This is my title<title>
<link rel="stylesheet" href="styles.css" type="text/css" />
<script src="script.js"></script>
.
. Only JS needed
. during page load
</head>
* Depends on size and whether major / minor breakpoints used
43. Load remaining Javascript late as possible
.
.
.
<script src="restofscript.js"></script>
</body>
</html>
One file or many?
(Depends on size)
Script loaders can help but scripts aren’t discoverable by pre-fetcher
44. The Script Tag
<script src=″…″></script>
Until the script has executed, the rendering of
all elements below is blocked!
45. “Virgin Media Broadband ISP Users
Affected by Website Routing Woes”
ISP Review, May 26, 2012
Customer jcmm33 said:
“Same issue here as well, been like this all day. Sites like
autotrader.co.uk don’t appear to be accessible, others like
the telegraph.co.uk are waiting on other components to
download (content from sites like cg-global.maxymiser.com,
pixel.quantserve.com).”
http://www.ispreview.co.uk/index.php/2012/05/uk-virgin-media-broadband-isp-users-affected-by-website-routing-woes.html
46. Impact on The Telegraph…
Same issue affected many other sites http://bit.ly/Ncy7Rd
47. Load Third Party scripts asynchronously
<script type="text/javascript">
function() {
var js = document.createElement('script');
js.async = true;
js.src = 'myscript.js';
var e = document.getElementsByTagName('script')[0];
e.parentNode.insertBefore(js, first);
})();
</script>
Or use a script loader - labjs, requirejs, yepnope etc.
48. Lots of factors to think about...
http://www.flickr.com/photos/corneveaux/3248566797
49. Don’t have to do it all by hand
http://www.flickr.com/photos/simeon_barkas/2557059247
