Design And Implementation Of Corba-based Adaptive Load Balancing Service

Load balancing is an increasingly popular and effective technique that can improve the overall performance of the distributed system and fulfill the needs of applications in high demand of scalability and availability. It can be implemented at various levels in a distributed system. Middleware-based load balancing has more advantages over network-based, OS-based and application level load balancing, such as shielding heterogeneousness and providing transparency and scalability.This thesis focuses on middleware-based load balancing supported by CORBA, and has made the following contributions:(1) Based on the previous research, we give a method using resource utilization and harmonic mean performance to quantify the load of each node in the heterogeneous environment, which makes the loads comparable. (2) We systematically review the main components of dynamic load balancing: transfer policy, location policy, information policy and selection policy that are the basic points of load balancing researches. (3) We analyze the mechanisms mandated by the CORBA specification to develop load balancing. Both the 'servant locator and the portable interceptor can throw ForwardRequest exception indicating that the ORB should forward the client request to other object transparently and portably. (4) In view of the insufficiencies of existing solutions, we design a load balancing service with certain fault tolerance at CORBA service level, striving for more scalability, adaptivity and transparency. (5) We present an adaptive load balancing algorithm which avoids binding a large number of bursting requests to the same object and dispatching tasks under the over-loaded situation. Experimental results demonstrate that our algorithm performs more effectively than conventional approaches especially when the system has heavy burden.