headroom — design for the scale you actually have (and the next one)

The first question is never "which database". It is: what scale exists now, and what scale are we actually designing for? Every recommendation that follows carries the load level at which it becomes necessary. A 50-user college project must not become Netflix — and a system about to 10× must not pretend a single box is fine forever.

When NOT to use

• Documenting what exists → blueprint.
• A specific endpoint is slow → that's diagnosis (hotpath), not design.
• Implementing backend behavior → backend.

Prerequisites