Multi-tenancy and resource sharing are essential to make a Database-as-a-Service (DaaS) cost-effective. However, one major consequence of resource sharing is that the performance of one tenant's workload can be significantly affected by the resource demands of co-located tenants. The lack of performance isolation in a shared environment can make DaaS less attractive to performance-sensitive tenants. The authors' approach to performance isolation in a DaaS is to isolate the key resources needed by the tenants' workload. In this paper, they focus on the problem of effectively sharing and isolating CPU among co-located tenants in a multi-tenant DaaS.