Multi-Tenancy

Multi-tenancy is a software architecture in which a single instance of an application serves multiple tenants (customers, organizations, or user groups) while maintaining logical or physical separation of each tenant's data. Multi-tenancy approaches include: shared database with shared schema (tenant ID column in each table—simplest, least isolation), shared database with separate schemas (one schema per tenant—moderate isolation), and separate databases per tenant (strongest isolation, highest cost). Multi-tenancy is the dominant architecture for SaaS applications as it enables efficient resource utilization, simplified management, and cost-effective scaling. Security considerations include ensuring queries never leak data across tenants, which is often enforced through row-level security policies.