Station-wagons and electrons

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Yahoo! London Pub Night – May 27, 2010 – Wallacespace Station wagons and Electrons

Not stuck in a cloud of volcanic ash

Didn’t get sidetracked on my way here

Didn’t go on an extended vacation

Almost not allowed in

Philip Tellisgeekyahoo@bluesmoonhttp://bluesmoon.info/philip@bluesmoon.info

Station wagons and Electrons

Philip Tellis / philip@bluesmoon.info

Yahoo! London Pub Night – May 27, 2010 – Wallacespace

Never underestimate the bandwidth of a station wagonspeeding down the motorway

– Andrew S Tanenbaum?

Should you fly a 747 or a 737?

A 747 seats 400+ passengersA 737 seats about 150Both take about the same time to fly from FRA to LHRA 747 takes longer to load and unload

The best selling aircraft to date is the 737

This analogy would have been much cooler if the Concorde still flew

Bandwidth and Latency

How much data can you transfer at oncev/s

How quickly can you get your data across

But bandwidth is easy

Shannon’s Theorem

C = B × log2(1 +SN

C – Channel capacity in bpsB – Bandwidth in HzS – Signal strengthN – Noise strength – S/N measured in dB

Bandwidth can be bought

Bandwidth has increased steadily over timeNetworks, hard drives, memory, CPU, system bus,everything.Bandwidth can be parallelised

Diminishing returns

The benefits of increased bandwidth diminish as you get fatter

Ref: More bandwidth doesn’t matter (much) – Mike Belshe

How fast is the internet?

YUI Blog measured bandwidth at 1Mbps and latency of 262ms

Ref: Analysing Bandwidth & Latency – YUI Blog

The average human eye takes 300-400msto blink

How fast is the internet?

Akamai measured average global bandwidth at 1.7Mbps

Ref: State of the Internet – Akamai

UK ISPs

Keep in mind that the Internet latency from the UK to the US is 90-100ms

Latency – not so easy to sell

Speed Limits

3× 108 m/s – in vacuum2× 108 m/s – in fibre=⇒ 26.42ms × 2(roundtrip from BOS to LON)

Round-trip

It should take a packet around 53ms to go from Boston toLondon and backIt actually takes around 90ms for a packet to go fromBoston to London and backThis is pretty good as far as approaching theoretical limitsgoes

Ref: It’s the latency, stupid – Stuart Cheshire

Round-trip

It should take a packet around 53ms to go from Boston toLondon and backIt actually takes around 90ms for a packet to go fromBoston to London and backThis is pretty good as far as approaching theoretical limitsgoes

Ref: It’s the latency, stupid – Stuart Cheshire

But then again...

Never underestimate the data-transfer capabilities of aGalaxy class starship travelling at Warp 9.875 andfitted with a computer that sounds like Majel Barett

Latency isn’t sexy

When was the last time you saw a TV commercial mentionlatency?

UK ISPs

Keep in mind that the Internet latency from the UK to the US is 90-100ms

Latency v/s Bandwidth

Improving latency tends to improve perceived bandwidthImproving bandwidth utilisation can potentially worsenlatencyLarger/complex packets take more time to assemble

This is the difference between a 737 and a 747

Getting around latency problems

Don’t add latency – It’s bad enough without us adding to itCaching – Bring the data closer to where it’s neededParallelise – Reduce the number of serial roundtripsPredict – Get data before it’s needed

If you can, stuff everything into one callHave a look at search.yahoo.com load up in firebug

Parallelise where possible

Downloading a script blocks page load, so do it in thebackground insteadBrowsers will download 4-8 resources from a host inparallel, take advantage of that

Predict what’s next and fetch it

If you know what the user will do next, pre-fetch itYahoo! Search page pre-loads sprites and Javascript forthe results pageLog analysis can tell you which pages are most popular,and pre-fetch those

Ref: Preload CSS & JS without execution – Stoyan Stefanov

Measure your user’s bandwidth & latency

Javascript code to measure your user’s bandwidth & latencyhttp://bluesmoon.info/perf-tests/bw/bw-test-1.3.ziphttp://github.com/bluesmoon/netperf-js

It’s what we used on the YUIBlog test

Useful tools for performance analysis

YSlow – Firefox/Firebug plugin from Yahoo!PageSpeed – Firefox/Firebug plugin from GooglePageTest – Web page testing toolShowSlow – Automated YSlow runs against your URLFiddler – Web debugging Proxy

Station-wagons and electrons

Technology