Foundations and Estimation

The math that settles design arguments before they start: back-of-envelope estimation, the latency numbers every engineer should know, SLOs, and capacity planning.

1. 01·Estimation Settles Design ArgumentsTwo engineers argue about scale until someone does the arithmetic. The four numbers every estimate starts from, and how to run them in your head.6m
2. 02·The Latency Numbers Worth Knowing by HeartMemory, SSD, network, cross-region: the ratios between them decide most designs. The numbers worth memorizing, and the two comparisons that matter.6m
3. 03·Your Average Latency Is Lying to YouThe mean hides the incident. What p99 measures, why tail latency amplifies across fan-out, and why you can never average percentiles together.6m
4. 04·SLIs, SLOs, and the Error BudgetAn availability target is a spending decision, not a wish. How to pick an indicator users feel, set a number you can defend, and spend the budget.6m
5. 05·Capacity Planning Without a Crystal BallLatency does not degrade gently as load rises, it collapses. Little's Law, why 80% utilization is the wall, and how much headroom to actually keep.6m
6. 06·Capstone: Size a System in Ten MinutesOne brief, worked end to end: users to QPS, QPS to instances, storage to five years, an SLO, and the headroom to defend it. The same walk every time.7m