System Design
Beginner

Capacity Estimation and Bottlenecks

Estimate traffic, storage, throughput, and the first constraints before picking technologies.

30 min
3 sections
capacity
latency
throughput
1
2
3

01. Estimate from product behavior

Section 1 of 3

Start with daily active users, actions per user, read/write ratio, payload size, and retention. The goal is not exact math; it is finding which subsystem becomes expensive first.

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Example: notification preferences service

10M monthly users
2M daily active users
5 reads per active user per day
0.2 writes per active user per day

Reads: 10M/day, about 116/sec average
Writes: 400K/day, about 5/sec average
Peak multiplier: 20x during campaigns
Peak reads: about 2.3K/sec
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