What is the difference between the three multi-tenant database patterns?

Separate Database: one database per tenant. Maximum isolation, easy backup per tenant. Cons: very expensive, hard to manage at 1000 tenants, sharing schema changes across tenants is complex. Separate Schema: one database, one schema per tenant. Good isolation (schemas are separate namespaces). Cons: 1000 tenants = 1000 schemas, connection pool complications. Shared Schema: one database, one schema