Confused with Server estimate

In the queries per second estimate, it came out that we are estimating 76 URL shortening requests per sec. and about 7.6K redirect requests per sec. This sounds very reasonable to me.

And, now in the Server estimates we are saying we need about 12,500 servers based on “back of the envelope” calculation.

When my QPS are saying at max I have 8K requests per sec, how does it justify 12,500 servers estimate ? I am sure, putting these numbers on the board during interview would raise flags.

Course: Grokking Modern System Design Interview for Engineers & Managers - Learn Interactively
Lesson: Requirements of TinyURL's Design


I think it is wrong. 1 server is enough for that. 7.6K / 8K < 1.

Hi Ravi and Si_Zhang,

We have revamped the “Back-of-the-envelope calculations” throughout the course. Please give it a read for a better understanding of the topic.

Thank you & regards,