How does Rails support multi-tenant database isolation strategies at scale?

Rails supports row-level, schema-level, and database-level isolation for multi-tenancy.

Multi-tenancy can be implemented in three ways: (1) shared database with tenant_id filtering (row-level isolation), (2) separate schemas per tenant (schema isolation), and (3) separate databases per tenant (full isolation). Each has trade-offs in scalability, cost, and complexity. Rails uses tools like ActsAsTenant or custom Current attributes to enforce scoping. At scale, schema/database per tenant is preferred for high isolation.