Adaptive window scheduling for a hierarchical agent system

DIET (distributed interactive engineering toolbox) is a toolbox for the construction of network enabled server (NES) systems. For most NES systems, as for most grid middleware systems, the scheduling system is centralized and can suffer from poor scalability. DIET provides an alternative: low-latency, scalable scheduling services based on a distributed hierarchy of scheduling agents. However, the online scheduling model used currently in DIET can overload interactive servers in high-load conditions and does not allow adaption to task or data dependencies. In this article we consider an alternative model based on active management of the flow of requests throughout the system. We have added support for (1) limiting the number of concurrent requests on interactive servers, (2) server and agent-level queues, and (3) window-based scheduling algorithms whereby the request release rate to servers can be controlled and some re-arrangement of request to host mappings is possible. We present experiments demonstrating that these approaches can improve performance and that the overheads introduced are not significantly different from those of the standard DIET approach