Put Back-of-the-Envelope Numbers in Perspective

Why back-of-the-envelope calculations?

A distributed system has compute nodes connected via a network. There is a wide variety of available compute nodes, and they can be connected in many different ways. Back-of-the-envelope calculations help us ignore nitty-gritty details of the system (at least at the design level) and focus on more important aspects.

Examples of the back-of-the-envelope calculation could be:

• Number of concurrent TCP connections a server can support
• Number of Requests Per Second (RPS) a web, database, or cache server can handle
• Storage requirements of a service

Choosing an unreasonable number for such calculations can lead to a flawed design. Since we will need good estimations in many design problems, we will discuss related concepts in detail here including:

• Types of data center servers
• Realistic access latencies of different components
• Estimation of RPS a server can handle
• Examples of bandwidth, servers, and storage estimation

Types of data center servers

Data centers do not have a single type of server. Enterprise solutions use commodity hardware to save cost and develop scalable solutions. Below we discuss the types of servers that are commonly used within a data center to handle different workloads.