Row-Level Multi-Tenancy Wins for Most SaaS Backends

Multi-tenant SaaS architecture has three main models: row-level, schema-per-tenant, and database-per-tenant. Row-level multi-tenancy with PostgreSQL Row-Level Security is the best default for most B2B products due to low cost and easy scaling. Stronger isolation is only needed for regulatory requirements, noisy neighbors, or per-tenant customization.