Back-of-the-Envelope Estimation
Before designing anything, you need a rough idea of its size. How many requests per second? How much storage? Back-of-the-envelope estimation is quick, approximate math that tells you whether a design will work, using a few numbers every engineer should know. As Jeff Dean put it, these are estimates you build from thought experiments and common performance numbers.
- 2.1Power of twoData volume can get enormous, but the math always comes down to the basics. A byte is 8 bits, and one ASCII character takes one byte. Every…
- 2.2Latency numbers every programmer should knowGoogle's Jeff Dean published how long typical computer operations took (2010). Hardware is faster now, but the ratios still hold, and…
- 2.3Availability numbersHigh availability is a system's ability to keep running for a long time. We express it as the percentage of time the service is up: 100%…
- 2.4Example: estimate Twitter QPS and storageLet's practice with made-up (not real) Twitter numbers. 📝 Assumptions 300 million monthly active users 50% use it daily 2 tweets per user…
- 2.5Tips for estimatingEstimation is about the process, not a perfect answer. Interviewers want to see how you think. Rounding and approximation. Don't compute…