The document discusses the importance of web performance, particularly load times, and their effect on user experience and conversion rates. It highlights that even slight improvements in page load times can significantly boost engagement and sales, with studies showing that slower sites lead to increased abandonment rates and negative brand perception. The text also mentions technological advancements such as HTTP/2 that can potentially improve performance and user satisfaction.

1. http://www.flickr.com/photos/barkaway/342359810
Speed is Essential for a
Great Web Experience
Andy Davies
NCC Group

3. https://www.flickr.com/photos/joelhughes/8743984985

4. http://www.flickr.com/photos/randomidea/247994072
Performance isn’t always a priority

5. https://www.flickr.com/photos/sharynmorrow/643126727
“Has it loaded yet?”

6. 100ms
1s
10s
Response Time in Man-computer Conversational Transactions
Robert B. Miller, 1968
Instant
Seamless
Yawn!
How we perceive response times

7. 100ms
1s
10s
Response Time in Man-computer Conversational Transactions
Robert B. Miller, 1968
Instant
Seamless
Yawn!
How we perceive response times
Only 12% of the top 100 (US) retail sites rendered
feature content in less than 3 seconds.

8. “50% more concentration when using
badly performing web sites”
Foviance
http://www.flickr.com/photos/yourdon/3366991042

9. Delay increases abandonment rate...
Abandonment rate over 200+ sites / 177+ million page views over 2 weeks - http://www.measureworks.nl / Gomez

10. …and has a negative impact on brand perception
Tesco’s ‘Fast’
Tesco’s ‘Slow’
Mobile Web Stress: Understanding the Neurological Impact of Poor Performance, Tammy Everts, Radware

11. We’re more tolerant as we get further into funnels
Less Tolerant
More Tolerant

12. and suspicious if something’s too fast

13. and suspicious if something’s too fast

14. Reader panel (3,000 people) rated speed (fast page load
time) as their second most important driver!
Speed had the highest percentage of people saying it was
VERY important to them

15. Faster experiences improve conversion
Walmart 2012

16. increased conversions by 10%
Shaved 1 second off median home page time!
6 seconds off 98th percentile
http://www.slideshare.net/cliffcrocker/velocity-ny-how-to-measure-revenue-in-milliseconds

17. Bing carried out some experiments
$/
+1s - 2.8%

18. Shopzilla cut page load time by 5 seconds!
+12% +25% -50%
http://velocityconf.com/velocity2009/public/schedule/detail/7709
$$$

19. Seatwave - below 4 secs vs. above 4 secs
+28% 2x 1/6
http://www.slideshare.net/pdyball/velocity-eu-2013-what-is-the-velocity-of-an-unladen-swallow
✔
凝

20. But I’m frustrated…
http://www.flickr.com/photos/sybrenstuvel/2468506922

21. The Web is Too Slow
http://www.flickr.com/photos/the_justified_sinner/3507390621

24. Too many sites are too slow
http://www.flickr.com/photos/the_justified_sinner/3507390621

25. and it’s getting worse!
Only 12% of the top 100 (US) retail sites rendered
feature content in less than 3 seconds. !
!
Year-on-year the median page has slowed down
by 23%
Tammy Everts - Radware State of the Union Fall 2014

26. “We’re not being deliberate about performance”!
Tim Kadlec
https://www.flickr.com/photos/lukew/7382528728

27. But only if we build it that way…
http://3.bp.blogspot.com/-0RqujOyE1ro/Up9HF7bPxbI/AAAAAAAAAbM/Ijudm6uq-dg/s1600/This+is+for+Everyone.jpg

28. We need to understand our fundamental building blocks
https://www.flickr.com/photos/ogimogi/2253657555

29. Everyone has fast broadband now… Right?
https://www.flickr.com/photos/98640399@N08/9287370881

30. Speed (Mbps)
18
16
14
12
10
8
6
4
2
0
Nov 08
Apr 09
May 10
Nov 10
May 11
Nov 10
May 12
Nov 11
May 13
Nov 12
Nov 13
UK Broadband speeds are rising…
Ofcom

31. But ‘Real Users’ experience varies
Visitors (%)
1 2 3 4 5 6 7 8 9 10
Load Time (s)
1%
3% 3%
2%
6%
8%
13%
27%
8%
6%

32. 24%
1%
3% 3%
2%
6%
But ‘Real Users’ experience varies
8%
13%
27%
8%
6%
Visitors (%)
1 2 3 4 5 6 7 8 9 10 > 10
Load Time (s)

33. and bandwidth (often) isn’t the bottleneck
0s 5s 10s
news.bbc.co.uk tested via webpagetest.org throttled at 1.5Mbps
(bursts over 1.5Mbps are artefact of testing)
2.0
1.5
1.0
0.5

34. Which will be faster?
1Mbps 10Mbps

35. Which will be faster?
1Mbps 10Mbps

36. Which will be faster?
1Mbps / 28ms RTT 10Mbps / 280ms RTT

37. We often think of the network as a pipe
https://www.flickr.com/photos/63567936@N00/4181042889

38. that’s sometimes really bad
https://www.flickr.com/photos/chesh2000/4487000196

39. but the reality is closer to
http://1m0esx2939yhjwld8419obqhyb.wpengine.netdna-cdn.com/wp-content/uploads/2014/06/DSC_0492.jpg

40. “More Bandwidth Doesn’t Matter (much)”
Mike Belshe
Page Load Time
1.41s 1.39s 1.38s 1.37s 1.36s 1.50s 1.44s
1 2 3 4 5 6 7 8 9 10
Bandwidth (Mbps)
1.63s
1.95s
3.11s

41. Latency has linear impact on user experience
4
3
Page Load Time (s) 1
2
0 20 40 60 80 100 120 140 160 180 200 220 240
Round Trip Time (ms)

42. Latency increases with distance
http://BT Backbone roundtrip times from London: http://ippm.bt.net/hour/europe/lo.shtml www.vectortemplates.com

43. Latency increases with distance
81ms
201ms
156ms
266ms
232ms
28ms
http://BT Backbone roundtrip times from London: http://ippm.bt.net/hour/europe/lo.shtml www.vectortemplates.com

44. There’s the last mile latency too
(and routers, other networking kit, mobile latencies too)
https://www.flickr.com/photos/kiwanja/3170292282

45. (TCP Segments)
TCP and the Lower Bound of Web Performance
John Rauser
Larger downloads == more round trips
285kB
214kB
143kB
71kB
1 2 3 4 5 6 7 8 9 10 11
Round Trips
Size

46. Latency is one of our greatest enemies
https://www.flickr.com/photos/jjvaca/728072059

47. We can cheat the latency penalty
(sometimes)
https://speakerdeck.com/mikeyk/secrets-to-lightning-fast-mobile-design

49. User gets
feedback

50. Network request
still in progress
User gets
feedback

51. But there’s plenty of recipes to work around it

52. Some of the optimisations are hacks!
https://www.flickr.com/photos/rocketnumber9/13695281

53. Browsers support more parallel connections
Old browsers - 2 parallel connections
Today’s browsers - 4 plus connections

54. We split resources across domains
www.bbc.co.uk!
static.bbci.co.uk!
news.bbcimg.co.uk!
node1.bbcimg.co.uk

55. DataURIs
url(data:image/
png;base64,iVBORw0KGgoAAA
ANSUhEUgAAABkAAAAZCAMAAAD
zN3VRAAAAGXRFWHRTb2Z0d2Fy
ZQBBZG9iZSBJbWFnZVJlYWR5c
cllPAAAAAZQTFRF/
wAAAAAAQaMSAwAAABJJREFUeN
piYBgFo2AwAIAAAwACigABtnC
V2AAAAABJRU5ErkJggg==)
=

56. DataURIs
Larger downloads (needs gzip)!
Overrides browser priorities
url(data:image/
png;base64,iVBORw0KGgoAAA
ANSUhEUgAAABkAAAAZCAMAAAD
zN3VRAAAAGXRFWHRTb2Z0d2Fy
ZQBBZG9iZSBJbWFnZVJlYWR5c
cllPAAAAAZQTFRF/
wAAAAAAQaMSAwAAABJJREFUeN
piYBgFo2AwAIAAAwACigABtnC
V2AAAAABJRU5ErkJggg==)
=

57. Create CSS and JavaScript bundles
+ + + +
= =

58. Create CSS and JavaScript bundles
+ + + +
= = More to download
and parse

59. Create CSS and JavaScript bundles
+ + + +
= = More to download
and parse +! x
!
Whole bundle is
invalidated if a
single file changes

60. CSS Sprites

61. CSS Sprites
To get just one sprite …

62. CSS Sprites
To get just one sprite …
Browser must download and
decode the whole image

63. There’s a tension between development and delivery
https://www.flickr.com/photos/domiriel/7376397968

64. Build tools and optimisation services help plug gaps
and won’t be going away…

65. But couldn’t we be more efficient?
https://www.flickr.com/photos/belsymington/4102783610

66. HTTP/2
(Evolved from Google’s SPDY)

67. Single multiplexed connection to host
HTTP/2
HTTP/1.1

68. Multiplexing offers interesting possibilities

69. How much of an image do we need to make it usable - 5%?
Experiment by John Mellor at Google

70. How much of an image do we need to make it usable - 15%?

71. How much of an image do we need to make it usable - 25%?

72. How much of an image do we need to make it usable - 80%?

73. How much of an image do we need to make it usable - 80%?
There are some questions
over the user experience with
progressive images

74. HTTP/1.1 - browser sets priorities

75. HTTP/2 - browser hints priorities
server can override them

76. Adds header compression too

77. Google and Mozilla will only support over HTTPS
http://www.flickr.com/photos/forsytht/4553656244

78. HTTP/2 rollouts will start next year - we still have a lot to learn
http://www.flickr.com/photos/atoach/6014917153

79. ???

80. Covert HTML …
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<script src="script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
</body>
</html>

81. … into Document Object Model (DOM)
html
head body
meta link script title h1 p
img

82. Convert CSS …
body { font-size: 16px }
h1 { text-decoration: underline}
p { font-weight: bold }
p > span { color: #000 }
img { border: 1px solid #ccc }

83. … into CSS Object Model (CSSOM)
body
h1 p
span
font-size: 16px
font-size: 16px
text-decoration: underline
font-size: 16px
font-weight: bold
font-size: 16px
font-weight: bold
color: #000
img
font-size: 16px
border: 1px solid #ccc

84. Combine DOM and CSSOM to build Render Tree
body
h1 p
img
font-size: 16px
text-decoration: underline
font-size: 16px
font-weight: bold
font-size: 16px
font-weight: bold
border: 1px solid #ccc

85. Render the Page
HTML
CSS
DOM
CSSOM
Render!
Tree
Layout Paint

86. But what about JavaScript?
HTML
CSS
DOM
CSSOM
Render!
Tree
JavaScript Layout Paint

87. But what about JavaScript?
HTML
CSS
DOM
CSSOM
Render!
Tree
JavaScript
Layout Paint
JavaScript blocks DOM construction!
CSSOM construction blocks JavaScript execution

88. Let’s pretend we’re a browser
(with the preloader switched off)
https://www.flickr.com/photos/mozillaeu/11171168996

89. Two key rules to remember
Constructing CSS Object Model (CSSOM) blocks JavaScript execution!
!
JavaScript blocks DOM construction

90. GET example.html HTTP/1.1

91. GET example.html HTTP/1.1

92. GET example.html HTTP/1.1

93. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

94. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

95. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
GET /styles.css HTTP/1.1
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

96. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

97. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>
GET /more-styles.css HTTP/1.1

98. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

99. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
GET /script.js HTTP/1.1
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

100. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

101. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

102. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>
Must wait for:!
1. CSS download and OM construction!
2. JS download and execution

103. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

104. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>
GET /another-script.js HTTP/1.1

105. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

106. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

107. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
Must wait for:!
<body>
1. JS download and execution
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

108. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

109. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>
GET /image.jpg HTTP/1.1

110. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>

111. example.html
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<link href="styles.css" rel="stylesheet">
<link href="more-styles.css" rel="stylesheet">
<script src="script.js"></script>
<script src="another-script.js"></script>
<title>HTML Example</title>
</head>
<body>
<h1>Title</h1>
<p>Some introductory text and picture! <img src="image.jpg"/></p>
<p>Some more text and another picture! <img src="image-2.jpg"/></p>
</body>
</html>
GET /image-2.jpg HTTP/1.1

112. http://www.flickr.com/photos/nozzer/3990622685
Pre-loader hides some of the latency penalty
So our pages load 20% faster

113. Structure pages for the browser’s critical path
HTML
CSS
DOM
CSSOM
Render!
Tree
JavaScript Layout Paint

114. Get the <head> straight
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>This is my title<title>
!
<link rel="stylesheet" href="styles.css" type="text/css" />
!
<script src="script.js"></script>
.
.
.
</head>
CSS before JS!
Ideally one file
Only JS needed
for page load

115. Load remaining JavaScript late as possible
!
.
.
.
!
<script src="restofscript.js"></script>
!
</body>
</html> One file or many?

116. Use async attribute to avoid blocking DOM
!
<script async src="myscript.js"></script>
Widely supported (82%) doesn’t incur delays of using inline
script to load other scripts e.g. Google Analytics snippet
http://caniuse.com/script-async

117. HTML
CSS
DOM
CSSOM
Render!
Tree
JavaScript Layout Paint

118. HTML
CSS
DOM
CSSOM
Render!
Tree
Fonts and background
images discovered
when render tree builds
JavaScript Layout Paint

119. And we all hate this… right?

120. Use font foundries that prioritise our visitor’s experience
http://www.flickr.com/photos/splorp/4951916342

121. Browsers pull resources from the server but …
https://www.flickr.com/photos/steveweaver/2915792034

122. https://www.flickr.com/photos/christian_bachellier/582457911
What if the server could push them?

123. Browser Server
Server
builds
page
GET index.html
<html><head>…
Loading a web page
Request other page resources

124. Browser Server
Server
builds
page
GET index.html
<html><head>…
Network
Idle
Request other page resources
Loading a web page

125. Browser Server
Server
builds
page
GET index.html
Push critical resource e .g. CSS
<html><head>…
Server Push
Request other page resources

126. Browser Server
Server
builds
page
GET index.html
Push critical resource e .g. CSS
<html><head>…
Request other page resources
Server Push

127. Browser Server
Server
builds
page
GET index.html
Push critical resource e .g. CSS
<html><head>…
Request other page resources
Server Push
Browser can reject push

128. We need to be deliberate, to design for performance
https://www.flickr.com/photos/9760699@N08/3748770917

129. http://www.flickr.com/photos/communityfriend/2342578485
Set performance budgets

130. Setting a budget
An event that matters to the visitor!
within a set time!
under defined network conditions

131. “Usable within 10 seconds on GPRS connection”!
BBC News

132. “SpeedIndex under 1000”!
Paul Irish

133. Could use page size or number of objects but…

134. …how well would they work here?

135. Measure frequently - during build and in live
http://www.flickr.com/photos/chandramarsono/4324373384

136. Make performance visible
Lara Hogan, Etsy

137. !

138. Lara Hogan, Etsy

139. http://lafikl.github.io/perfBar

140. Compare against competitors

141. The Guardian display their performance on a monitor by FD’s office

142. Remember the constraints of our medium
https://www.flickr.com/photos/33649815@N03/3367739514

143. https://www.flickr.com/photos/basheertome/4762529213