The database is one of the few decisions that is genuinely hard to reverse once a product has real data in it. That makes it worth a little thought — and also makes it a magnet for overthinking. Teams burn weeks comparing exotic options for a product whose needs a boring, well-understood database would meet comfortably.
Here is a way to decide without either rushing it or turning it into a research project.
Start with a relational default
For most products, a mature relational database — PostgreSQL is a reliable default — is the right answer, and the burden of proof is on anything else. It handles structured data, relationships, and transactions well; it is widely understood, so hiring and debugging are easier; and it will take you much further than people expect before it becomes a limit.
Know what you are actually optimising for
The question is not "which database is fastest" in the abstract. It is which one fits how your data is shaped and used:
- Structured data with relationships and transactions — a relational database, comfortably.
- Flexible or rapidly changing document shapes — a document store can help, though modern relational databases handle JSON well enough that this is a weaker argument than it used to be.
- Full-text search or analytics at scale — often a purpose-built tool alongside your primary database, not a replacement for it.
"It won't scale" is usually premature
The fear that a relational database will not scale drives a lot of early over-engineering, and it is almost always premature. A well-designed relational database on decent hardware serves a very large product before scale becomes the real constraint. Solve the problem you have, not the one you imagine having at a size you have not reached.
Choosing an exotic database to solve a scale problem you do not have yet usually just gives you an operational problem you do have now.
You are allowed more than one
Picking a primary database is not a vow of monogamy. A common, sensible shape is a relational database as the source of truth, with a dedicated search index or cache alongside it for the jobs it is not best at. The mistake is reaching for the specialised tool first and trying to make it do everything.
The decision, in one line
Default to a relational database. Move away from it only when you have a specific, present need it genuinely cannot meet — and even then, more often as an addition than a replacement.