Don't Forget The Network: Your App Is Slower Than You Think (RailsConf 2016)

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don't forget the network your app is slower than you think

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André Arko @indirect

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The Ruby Way therubyway.io

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Routing

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Routing your app has this

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Routing how does it work?

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Development App You

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Production People Router Server App App Router Server App App Router

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Routing how slow is it?

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Routing does it back up?

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Request time

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Request time not the time you measure

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Request time wall-clock time from real clients

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Request time make requests from around the world

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Servers

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Servers you have no idea what is going on

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really.

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Runtime lag

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Runtime lag how do you tell you lost consciousness?

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Runtime lag you have it.

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Runtime lag you have it. how bad is it?

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VM lag

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VM lag do you have it?

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VM lag do you check for it?

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VM lag do you know how to check for it?

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Metrics

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Metrics are important

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Metrics tell you what is happening

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you rn →

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Metrics convince you you understand

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you later →

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Averages convince you you understand

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Averages are lie-candy for your brain

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“Normal” 5 -5 -4 -3 -2 -1 0 1 2 3 4 0 0.1 0.2 0.3 0.4

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“Normal” 5 -5 -4 -3 -2 -1 0 1 2 3 4 0 0.1 0.2 0.3 0.4

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Real Life 5 -5 -4 -3 -2 -1 0 1 2 3 4 0 0.1 0.2 0.3 0.4

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brendangregg.com

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brendangregg.com

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just heard “w e have a great average” →

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The problem with averages: If you put one hand in a bucket of ice and the other in a bucket of hot coals, on average, you’re comfortable. Erik Michaels-Ober @sferik

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Averages mask problems

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10 0 1 2 3 4 5 6 7 8 9 250 0 50 100 150 200

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Graph the median

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10 0 1 2 3 4 5 6 7 8 9 250 0 50 100 150 200

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Graph 95th percentile

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10 0 1 2 3 4 5 6 7 8 9 250 0 50 100 150 200

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Graph 99th percentile

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10 0 1 2 3 4 5 6 7 8 9 1000 0 250 500 750

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Aggregate graphs another average

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Breakout graphs show each source

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Seriously, do it Visualize your data

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graphic by Schutz and Avenue, CC-Attribution-ShareAlike, taken from from the Wikipedia article on Anscombe's quartet

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Average of X: 9 Average of X: 9 Average of X: 9 Average of X: 9

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Average of Y: 7.50 Average of Y: 7.50 Average of Y: 7.50 Average of Y: 7.50

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Average of X Average of Y Variance of X Variance of Y Correlation of X and Y Linear regression All four data sets have the same