Guides
Every guide, newest first (8).
2026
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Why does fan-out make fast services slow?
A request that waits for 100 parallel calls is as slow as the slowest of them: the arithmetic of Dean and Barroso's paper, and the same effect in a design you can run.
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Why does p99 latency explode long before 100 % CPU?
The queueing arithmetic for 1, 2 and 16 cores, what bursts do to it, our Postgres measurement, and the same curve in four designs you can open.
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How many users can a $12 server handle? We measured it
A $12-a-month VM with Nginx, Node.js and Postgres under virtual users: about 800 users at one second of think time, and a CPU throttle the guest does not show.
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How many requests per second can one Postgres handle?
One PostgreSQL on a 2-vCPU VM, measured: about 6,000 simple indexed reads per second at 100 % CPU, where p99 starts to climb, and how to estimate your own number.
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How big should your database connection pool be?
A pool of 4 against a pool of 16 connections on the same Postgres, measured, and Little's law for sizing your own.
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Cache hit ratio: what 80 % vs 95 % means for your database
The arithmetic of cache misses, and what a cold cache after a restart does to the database behind it.
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Retry storms: why retries take your service down
How retries multiply load, why a storm can outlive its trigger, and the fixes that work, shown in a design you can run.
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System design interview: the URL shortener, simulated live
The classic interview design with its numbers simulated over a real day of traffic: what breaks first, at which load, and what it costs.