1. A controller-executed method for scheduling mixed workloads comprising: balancing average stretch and maximum stretch of scheduled queries wherein query stretch is defined as a ratio of a sum of wait time and execution time to execution time of a query; modifying scheduling of queries in response to the balancing according to service level differentiation; and determining which query of a plurality of queries is to be executed by a database management system comprising: maintaining a single queue of queries for selection for execution by the database management system, assigning a rank to the query entries on the queue, wherein a higher rank is assigned to the query entries in order of lesser execution time, ordering the query entries on the queue according to the rank, and selecting a query of highest rank for execution in the database management system.