Back-of-the-Envelope Estimation
Powers of two, the one-day-is-1e5-seconds rule, and quick QPS, storage and bandwidth estimates that guide a design.
Why estimate at all
Design choices depend on scale. A system for 100 requests per second can be one server and one database. One for 100,000 cannot. An estimate tells you which world you are in.
- It is order of magnitude work: 1,000 versus 10,000 matters, 1,200 versus 1,500 does not.
- Round aggressively. State assumptions out loud. The interviewer checks your method, not your decimals.
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