Architectural Patterns for Multi-Tenant SaaS Backends

### Choosing the Right Isolation Model When building Software-as-a-Service (SaaS) platforms, selecting the database isolation strategy directly impacts security, query performance, and infrastructure operational cost. #### 1. Row-Level Security (Shared Database, Shared Schema) - **Pros**: Lowest infrastructure cost, simplified migrations, centralized backups. - **Cons**: Requires bulletproof tenant ID filtering on every query to prevent cross-tenant data leaks. - **Best For**: Early-stage SaaS products and standard B2B applications. #### 2. Schema-per-Tenant (Shared Database, Separate Schemas) - **Pros**: Stronger logical boundary, easier per-tenant data exports. - **Cons**: Schema migration complexity increases linearly with tenant count. #### 3. Database-per-Tenant (Isolated Databases) - **Pros**: Complete physical isolation, zero noise-neighbor performance impact, compliance friendly. - **Cons**: High infrastructure cost and complex global management pipelines. ### Recommendation For 90% of enterprise SaaS applications, PostgreSQL with Row-Level Security (RLS) policies enforced at the database driver level provides the optimal balance of speed, cost, and isolation security.