Requirements of Quora's Design - Grokking Modern System Design Interview for

RPS of a server
Number of daily active users

300×10^6 / 8000 =37500

but rps calculated in the previous line is : 69500

Hi Priya

The calculations performed are used to obtain the requests per second only, which is observed to be approx. 69,500. However, as mentioned in the line below, the calculations we have performed estimate the number of servers based on two numbers. i.e., the number of users on a daily basis and the number of requests a server can handle per second (300x10^6/8000). Which ultimately gives the number 37,500.

We have stated the reasons why 69500(the number of requests arriving per second)/8000 (the number of requests a server can handle per second) is not a suitable calculation to estimate a workable number of servers in the back-of-the-envelope calculations section.

We are currently working to revamp this section of the course to give an in-depth analysis and therefore, more clarity.

Hi, I believe your previous poster was correct. This section of the tutorial is wrong. If we assume approx. 69500 requests per second then the number of servers should be 69500/8000 = 8.688 (approx 9). This would be consistent with your section on the Instagram server calculation.

Your answer assumes all the requests for 300M users would arrive at the same second, which may technically be possible, but is highly unlikely and would lead to over-provisioning. The real answer lies somewhere between the two numbers (9 and 37,500). Given geographic distribution of users I would expect some request distribution.


Hi Sam.

Yes, your observation is correct. However, it is important to understand the context of these calculations. We estimate the maximum number of servers we would require in case we face a peak load. These numbers can vary in reality depending on various factors as discussed here.
If you have any further queries, feel free to reach out to us.

Thank you.