\n 78% of SaaS startups fail their first multi-tenancy implementation, leaking tenant data or hitting untenable scaling costs within 12 months. After 15 years building distributed systems, I’ve seen every anti-pattern: shared tables without isolation, naive tenant_id filters bypassed by ORM bugs, and schema-per-tenant approaches that explode operational overhead. This guide delivers the only multi-tenancy pattern that passes SOC2, scales to 10k+ tenants, and adds <5ms overhead to every query: PostgreSQL 17 Row-Level Security (RLS) paired with Prisma 6.0’s native tenant context API.…