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Notes on Distributed Systems for Young Bloods – Something Similar


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Use percentiles, not averages. Percentiles (50th, 99th, 99.9th, 99.99th) are more accurate and informative than averages in the vast majority of distributed systems. Using a mean assumes that the metric under evaluation follows a bell curve but, in practice, this describes very few metrics an engineer cares about. “Average latency” is a commonly reported metric, but I’ve never once seen a distributed system whose latency followed a bell curve. If the metric doesn’t follow a bell curve, the average is meaningless and leads to incorrect decisions and understanding. Avoid the trap by talking in percentiles. Default to percentiles, and you’ll better understand how users really see your system.

"Robust, open source distributed systems are much less common than robust, single-machine systems."

That was not intuitive to me at first, but it makes sense now that I think about it.

Thanks, you just improved my intuition.

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