Performance analysisclass

The Art and Science of
Web Performance

Daniel Austin
Technical Staff
Paypal, Inc.
CMU Invited Lecture
August 02 , 2012 daaustin@paypal.com
V1.1 @daniel_b_austin

TODAY’S PROGRAM

Overture: Web Performance As Art And
Science

First the Theory…

…Then the Practice

Coda: Making the Web Faster and Smarter

Confidential and Proprietary 8/2/2012

STATE OF THE ART?

• An Art and a Science
• Very Little Prior Art
• Users Suffer –
• The World Wide Wait isn’t over yet!
• Rapid Change in the Industry
• Browsers
• Devices
• Standards
• The Rest of the World is Catching Up
• Challenges of Global/Local/Mobile/Social
Performance

PERFORMANCE IS RESPONSE TIME




(It’s not latency, it’s not bandwidth, it’s not queue
residence time or queue length or any such thing.)


Who needs
‘Performance’
measurements
anyway?

?

Confidential and Proprietary

A MORE RATIONAL APPROACH?


DIMENSIONS OF PERFORMANCE

• Geography/Network location
• Bandwidth/Transport Type
• Browser/Device Type
• RT Varies by as much as 50%
• Page Composition
• Client-side rendering and execution
effects (JS, CSS)
• Network Transport Effects
• # of Connections, CDN Use


THE MPPC MODEL OF WEB PERFORMANCE
“Multiple Parallel Persistent Connections”
Request DNS/Network
Initiation by HTTP Request Resolution HTTP Request
User t1

This entire cycle, steps 1-4, is repeated once for each external
Page
reference on the page, so for a given page the total time is: Composition
S T = S Dt1 + Dt2 + Dt3 + Dt4 t2
n+1 n+1
End User Where n is the number of external page requisites.

Payload
Browser HTTP Response Delivery Time HTTP Response
Rendering Time t3
t4

T1 T2 T3 T4
Connection Time Server Duration Transport Time Render Time


HTTP CONNECTION FLOW

Client Server
Connection setup (t1)

Handshake time
Request transmission
Client’s perceived time
response time Request (t2) Estimated server
processing time
Response transmission
Response (t3)
time

The more HTTP requests & network roundtrips you require, the slower
your site will be: Images, CSS, JS, DNS lookups, Redirects, #of
packets


T1 – MAKING THE CONNECTION

1= DNS + TCP+ SSL

T2 – THE SERVER DURATION
• Let ( ) r

• U = ( r)[ r
W]

• X =U*

• Navg =
( r [W( r)W+1 -
(W+1)( r)W+1]

• … so 2 = Navg/X
(The response
time law)

Never mind - it’s a constant!


T3 – TCP TRANSPORT TIME

Single Object:

3 = Sz/R+2RTT+ idle

For persistent parallel connections:

3 = (M+1)Si/Ri+[M/kNh]*3 RTTi+ idle

… for 1 base HTML page with M objects, with Si
bits, at bandwidth Ri, k connections per
host, and Nh unique hostnames


T4 – WHAT THE BROWSER DOES


BANDWIDTH EFFICIENCY
Bmax = 1.22*(L)^1/2 * MSS/RTT


WHERE ARE THE DELAYS?


LET’S TALK TOOLS
Site Performance Services Page Analysis Tools
– Gomez – YSlow
– Keynote – MS Virtual RoundTrip
– WebPagestest.Org Analyzer,
• ‘Wholesale’ Testing HTTPWatch, Many
Others
– Statistical data for many
page views under different – F12 in your browser
conditions • ‘Retail’ Testing
– Operational testing – One Page or App
– Best for understanding – Diagnostic
global and network effects – Best for functional
testing


COMMERCIAL TESTING SERVICES
• Gomez, AlertSite, and Keynote toolsets are similar in many
ways
• Synthetic Test Setup
• Test nodes in large datacenters and/or end user’s machines
• Statistical data about response times

• You can do this for yourself on a smaller scale at
WebPageTest.org


HAPPY BIRTHDAY, YSLOW!

Methodology
– DOM Crawler and Packet
Sniffer
– More accurate
– Analyzes components
– Stats view

Implements the 14 18 22 105
YSlow Rules
– All browsers except IE
– Mobile bookmarklet
– Best tool for page analysis


TESTING YOUR COMPETITORS FOR FUN &
PROFIT
• Try to measure task sequences not pages
• Be prepared for lots of breakage
• Be respectful
• Difficult and time-consuming


TASK-BASED PERFORMANCE THINKING

Welcome 1400
Inbox 2200
Inbox Bulk 3200
(B) …
61.77%

P(A,B) = 0.5168
Read
10.04% 66.25% Message
(D) Verify
(F)
34.52%
Welcome 9.85% Bulk
(A) (C) 58.07%
64.53%
22.30% 34.38%

35.02%

Send
Compose28.04%
Confirm
(E)
(G)


GLOBAL PERFORMANCE TESTING (BRIEFLY)

• Cannot compare performance data out-of-region
• There are many global factors involved in
performance:
• Bandwidth
• ISP
• Infrastructure
• Secular cycles (weeks, holidays, usage patterns)
• The best approach: use the relative ‘StormCat’
system
• Best case (Northern California high broadband @3 AM)
• Worst Case (rural Indonesia on VSNL @ 2PM local)
• Divide the range into 5 categories equally spaced
between the best & worst: some locales will be in Cat I,
some in Cat II, some in Cat III, etc.

BAKE IT IN UP FRONT
Performance Engineering is a
design-time activity!

This is absolutely crucial!

Anti-Pattern: Releasing a
new or modified product
without testing its
performance.

Seriously.


QUANTIFY


KNOW THE LANDSCAPE
“What are the differences among browsers?”

“What are my competitors doing?”

“What about low bandwidth users?

“How can I test that?”


THE 7 HABITS OF EXCEPTIONAL
PERFORMANCE
1. Make Performance a Priority
2. Test, Measure, Test Again
3. Learn about the Tools
4. Balance Performance with Features
5. Track Results Over Time
6. Set Targets
7. Ask Questions; Check It for Yourself!


CODA: MAKING THE WEB SMARTER AND
FASTER

• Faster HTTP
• SPDY
• HTTP Speed+Mobility
• Scratch
• Better Browsers
• Chrome has disrupted the market
• HTML5 will drive further evolution
• Moving to Mobile/Device Platforms
• More sensitive to network effects of all kinds
• Application-driven user experience
• Moving away from Hypertext?

42

Michael Faraday is the father of network performance, having
performed the first bandwidth measurements on the first
transatlantic telegraph cable in 1854.

Daniel Austin
Technical Staff
CMU Invited Lecture Paypal, Inc.
August 02 , 2012
V1.1
daaustin@paypal.com
@daniel_b_austin

Performance analysisclass

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