If you're building a multi-tenant SaaS, this is the first real architecture decision that will haunt you if you get it wrong. I've implemented both approaches in production. Here's the honest trade-off. Option A: Shared schema with row-level security (RLS) Every tenant's data lives in the same tables. A tenant_id column on every row. PostgreSQL RLS policies enforce that queries only ever return rows belonging to the current tenant. -- Enable RLS on the table ALTER TABLE orders ENABLE ROW LEVEL SECURITY ; -- Policy: users only see their tenant's rows CREATE POLICY tenant_isolation ON orders USING ( tenant_id = current_setting ( 'app.current_tenant_id' ):: uuid ); Enter fullscreen mode Exit fullscreen mode # Set the tenant context before every query async def set_tenant ( conn , tenant_id : str ): await conn . execute ( " SELECT set_config( ' app.current_tenant_id ' , $1, true) " , tenant_id ) Enter fullscreen mode Exit fullscreen mode Works well when: You have many small tenants. Hundreds or thousands.…