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Enforcing time-constraints effectively for QoS-aware servers

One of the relevant Quality-of-Service (QoS) issues in web service provider infrastructures (Web-servers, web-services and backend database-servers) is how well they are able to handle congestion, while still meeting time-constraints for accepted transactions. There are many works proposing admission control mechanisms, but their focus is on throughput maximization under miss ratio constraints. These metrics are misleading -- at maximum service rate, throughput can only be improved by accepting small transactions while starving long ones. In this paper we investigate whether admission control based on time-constraints may be a more suitable solution, and analyze the hypothesis by means of simulation. We show that time-based control works well. These conclusions are a basis for our future work within the Adapt-DB project on: alternative time-bounding based control approaches; effective control of starving with best throughput; and especially on SLA-targets tracking and feedback control, all of them using timing control as a basis.