Implementing Multi-Tenant Architectures in PostgreSQL

The Multi-Tenant Problem

When building Enterprise B2B SaaS, isolating client data is the paramount concern. An unintended data leak between tenants kills companies overnight.

There are generally three approaches to multi-tenancy in PostgreSQL databases, but we strictly enforce only two.

Row-Level Security (RLS)

A shared-database, shared-schema setup. Every row in your system gets a tenant_id.

ALTER TABLE orders ENABLE ROW LEVEL SECURITY;

CREATE POLICY tenant_isolation_policy ON orders
  USING (tenant_id = current_setting('app.current_tenant_id')::uuid);

Using PostgreSQL RLS prevents engineers from ever accidentally forgetting a WHERE tenant_id = X clause. The database hard-enforces the limitation. We use this for SaaS modules up to 1,000 tenants where extreme schema migration synchronization is required.

Schema-per-Tenant Architecture

For larger applications managing disparate enterprise clients (banks, hospitals), we isolate completely at the schema level.

CREATE SCHEMA "tenant_alpha_corp";
SET search_path TO "tenant_alpha_corp";

This guarantees that SELECT * FROM users only fetches Alpha Corp's data. Migrations take longer (iterating over hundreds of schemas), but the backup/restore capabilities and raw isolation are drastically superior for compliance regulations.