Before revision:  While a class of O(n^{2.5} \log n) complexity hybrid scheduling policies are recently developed to guarantee both rate-function delay optimality (in the many-channel many-user asymptotic regime) and throughput optimality (in  general non-asymptotic setting), their practical complexity is typically high.
After revision:  While a class of O(n^{2.5} \log n) complexity hybrid scheduling policies are recently developed to guarantee both rate-function delay optimality (in the many-channel many-user asymptotic regime) and throughput optimality (in the general non-asymptotic setting), their practical complexity is typically high.