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LatencyThe King of the Mobile Experience
By Jeremy WilsonCTO, Keek Inc.
Who am I?
Jeremy Wilson
• 18 years experience in administrating and scaling web-based infrastructures to millions of daily users
• 8 years experience in optimizing for mobile devices
• Currently CTO of Keek, a social video startup in Toronto
What is Latency?
la·ten·cy [leyt-n-see]:A measure of time delay experienced in a system or network
due to various limitations in those systems or networks
What is Latency?
Person to Device• User Input• Screen Refresh• Transitions• Gestures
What is Latency?
Device to Network• Signal Strength• Connection type (3G, LTE)• Device Resources• Distance• Buffering
What is Latency?
Network to Internet• Bandwidth• Traffic Shaping• Routing• Buffering
What is Latency?
Internet to Server• Service Type• Caching• Physical Resources (Disk/CPU)• Databases• Clustering• Networking
What is Latency?
Then double it for the response time
Maximum total response time considered acceptable by serviceproviders such as Google
1 secondSource: https://developers.google.com/speed/docs/insights/mobile
People
Minimum duration for perception of an event to have occurred
100 millisecondsBelow this, events are perceived as instantaneous
Source: http://www.nngroup.com/articles/response-times-3-important-limits/
People
Maximum time for flow of thought to stay uninterrupted
1 second
Source: http://www.nngroup.com/articles/response-times-3-important-limits/
People
Maximum attention span without feedback
10 seconds
Source: http://www.nngroup.com/articles/response-times-3-important-limits/
People
Traffic drop when a page takes 500ms longer to load
20%Sales lost for every 100ms of delay
1%Source: http://glinden.blogspot.ca/2006/11/marissa-mayer-at-web-20.html http://blog.gigaspaces.com/amazon-found-every-100ms-of-latency-cost-them-1-in-sales/
People
are impatient and easily distracted
• Make your UI responsive• Minimize delays in switching screens
• Do work in the background• Provide feedback (like spinners) during
long operations• Avoid long operations altogether
Devices
CPU power and RAM strongly effect page load and display times
Page Load Times for iPhone Devices
iPhone 5 (3G) iPhone 5 (EDGE) iPhone 4 (3G)
4.3s 4.6s 12.1s
Response Time from US AT&T Network
Devices
are slow, have unpredictable resources and rely onremote systems you may not control
• Use local assets• Cache everything
• Offload slow jobs to APIs• Test on multiple devices
• Develop for the lowest powereddevice you plan to support
NetworksiPhone 5 on Rogers LTE Network to Google DNS Servers
Total routing hops Ping time
20 58msLaptop on 1Gb LAN to Google DNS Servers
Total routing hops Ping time
9 26msMobile networks have inefficient packet routing and highly throttled traffic shaping
Networks
Even on fast WiFi networks, each connection you make hasoverhead, which includes the response speed of the service
Source: https://developers.google.com/speed/docs/insights/mobile
Networks
have highly variable performance and significantconnection overhead
• Keep packets small• Avoid transferring large data - send multiple
chunks of small data instead• Try to maintain persistent connections - avoid
making new connections• Test on as many networks as possible
Internet
Security means latency
• SSL / HTTPS requires 3 or more send/receivetransactions to establish a connection• Encryption and decryption can add up to
20% additional connection overhead• Authentication methods require additional
data be transferred for each transactionSource: http://revocation-report.x509labs.com
Internet
security is important, but use it intelligently
• Consider SSL when designing your app andbuild the delays it imposes in from thebeginning• Restrict SSL connections to sensitivecommunication only, such as login or userupdates
• Use more efficient ciphers
Servers
Maximum speed means maintaining control and doing it yourself
• SaaS/PaaS systems are optimized for generalperformance, not specific to your app
• Managed servers are maintained by generalstaff and usually have 24 hour response times
• Self-managed Cloud servers are hosted onshared systems and do not offer consistentperformance
Servers
The Cloud is slow compared to physical hardware
Amazon EC2 Eight Extra Large (8 core)Max Requests / second Response Time
180,000 2,000msSoftlayer dual Intel Xeon X5670 (6 core)
Max Requests / second Response Time
500,000 1,500msSource: http://lowlatencyweb.wordpress.com/2012/03/21/modern-http-servers-are-fast-ec2-is-not/
Servers
Internal networking between servers takes time and is highly variable in the Cloud
Amazon t1.micro US-East-1c Zone (100 packets)Average Ping Time Maximum Ping Time
0.941ms 8.985msDedicated 10Gb Ethernet Network (100 packets)
Average Ping Time Maximum Ping Time
0.136ms 0.204msSource: http://lowlatencyweb.wordpress.com/2012/03/21/modern-http-servers-are-fast-ec2-is-not/
Servers
perform best on real hardware, but there is abalance between cost and maintainability
• Physical servers require administration andmaintenance and the skilled personnel toperform it
• Cloud is cheaper to start but more expensiveas you grow - consider hybrid or migratingafter gaining market traction
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