On Robust Transaction Routing and Load Sharing

In this paper we examine the issue of robust transaction routing in a locally distributed database environment where transaction characteristics such as reference locality imply that certain processing systems can be identified as being more suitable than others for a given transaction class. A response time based routing strategy can strike a balance between indiscriminate sharing of the load and routing based only on transaction affinity. Since response time estimates depend on workload and system parameters that may not be readily available, it is important to examine the robustness of routing decisions to information accuracy. We find that a strategy which strictly tries to minimize the response time of incoming transactions is sensitive to the accuracy of certain parameter values. On the other hand, naive strategies, that simply ignore the parameters in making routing decisions, have even worse performance. Three alternative strategies are therefore examined: threshold, discriminatory, and adaptive. Instead of just optimizing an incoming transaction's response time, the first two strategies pursue a strategy that is somewhat more oriented towards global optimization. This is achieved by being more restrictive on either the condition or the candidate for balancing the load. The third strategy, while trying to minimize the response time of individual incoming transactions, employs a feedback process to adaptively adjust future response time estimates. It monitors the discrepancy between the actual and estimated response times and introduces a correction factor based on regression analysis. All three strategies are shown to be robust with respect to the accuracy of workload and system parameters used in the response time estimation.