1. A computer-implemented apparatus for monitoring and managing a plurality of database systems, comprising: (a) a domain comprised of the plurality of database systems, wherein at least two of the plurality of database systems are each tuned for different types of workloads, each of the plurality of database systems are managed by one or more closed-loop system management (CLSM) regulators performed by one or more processors, each of the one or more CLSM regulators monitors system conditions and operating environment events for its database system, such that each of the one or more CLSM regulators aggregates information related to its database system as well as that of its children CLSM regulators, and reports the aggregated information to its parent CLSM regulator, and each of the one or more CLSM regulators manages workloads in its database system; and (b) a virtual regulator, performed by a processor and comprising a CLSM regulator at a highest level of the domain, for monitoring and managing the domain, wherein the virtual regulator communicates with the one or more CLSM regulators that manage the plurality of database systems to compile the aggregated information reported by the one or more CLSM regulators to monitor the system conditions and the operating environment events within the domain, and the virtual regulator manages workloads in the domain by routing whole queries or steps of the queries to a particular one of the plurality of database systems within the domain based on: (1) the system conditions and the operating environment events within the domain, and (2) a cost function that determines which of the plurality of database systems is used for the queries or the steps of the queries, based on how the plurality of database systems are each tuned for the different types of workloads.