Feedback Control-Based Database Connection Management for Proportional Delay Differentiation-Enabled Web Application Servers

As an important differentiated service model, proportional delay differentiation (PDD) aims to maintain the queuing delay ratio between different classes of requests or packets according to pre-specified parameters. This paper considers providing PDD service in web application servers through feedback control-based database connection management. To achieve this goal, an approximate linear time-invariant model of the database connection pool (DBCP) is identified experimentally and used to design a proportional-integral (PI) controller. Periodically the controller is invoked to calculate and adjust the probabilities for different classes of dynamic requests to use database connections, according to the error between the measured delay ratio and the reference value. Three kinds of workloads, which follow deterministic, uniform and heavy-tailed distributions respectively, are designed to evaluate the performance of the closed-loop system. Experiment results indicate that, the controller is effective in handling varying workloads, and PDD can be achieved in the DBCP even if the number of concurrent dynamic requests changes abruptly under different kinds of workloads.