Choosing the Right Database in a System Design Interview
"What database should we use?"
This question comes up in every system design interview. And most candidates give weak answers like "We will use PostgreSQL because it is reliable" or "Let's use MongoDB because it scales well."
These answers miss the point entirely.
Database selection is not about picking your favorite technology. It is about matching data requirements to database capabilities.
The right database for a messaging app is not the right database for an analytics pipeline. The right database for a payment system is not the right database for a social feed.
Interviewers ask about databases because your choice reveals how well you understand data requirements, trade-offs, and system constraints. A candidate who picks the right database and explains why demonstrates real engineering judgment.
In this chapter, you will learn:
- How to analyze data requirements before choosing a database
- The major database categories and when to use each
- A decision framework for system design interviews
- Real examples with database recommendations
- Common mistakes and how to avoid them