The Research On The Load Balancing Of CORBA-based Middleware

Middleware technologies for heterogeneous distributed systems have been built and used successfully in the industry for the past decade. Among others , the Common Object Request Broker Architecture(CORBA) is the popular standard for middleware which is far and widely used in distributed system. More and more attention of IT workers has been attracted on it. The most important character of CORBA is applying the high-degree interoperability between objects, which is distributed in complex net environment, so that the object which is built by different CORBA products can communicate with each other.And on the other hand, the demand for distributed systems with good performance and high scalability has been increasing over the past decade, load balancing has proven to be an effective way for achieving good performance and high scalability in distributed systems, and a great deal of research has been conducted in this domain in the past. By distributing client workload equally among back-end servers, overall system performance and scalability can be improved. In addition to distributed system in general, load balancing is also used in heterogeneous distributed environments that use CORBA-based middleware for achieving interoperability.Load balancing schemes of distributed systems are analyzed in this paper by the numbers. And loading balancing can divided into different types according to different criterion. Also, which loading balancing strategy or strategies are adopted is based on the characteristics of an applied system. Moreover, the design of load balancing system relates to the performance, response time and throughput of the system, which are the basic measures. Hence, a good load balancing system should follow the criterion of efficiency, stability, reliability, user transmittance, and versatility.The primary work of this thesis is to investigate CORBA-based load balancing strategies. Therefore, a testing scheme model is designed and realized. And three components, client, load balancer, server, are included. Respectively, client uses multithreading model to simulate multi-clients, then it transfers register service of the server. Afterwards, load balancer answers for layers of tasks according to different load balancing strategy. Finally, the request return time is recorded.Each strategy reflects a distinct combination of a request mapping policy and an interaction pattern among the three components in the load balancing system: client, server, balancer.Using the commercially available CORBA-compliant software Orbix2000,we designed and implemented a performance testing model of a load balancing system.And then the effects of different workload factors on the performances of the different load balancing strategies are measured,and derived results are also discussed.Particularly,a comparison of the effects of different workload on the performances of various load balancing strategies presented.Different load balancing strategies are proposed and their performances are evaluated.These strategies are Handle Driven (HD),Forword with reply coming from Balancer(FB),Forwarding with reply coming from Server(FS),Forwarding with reply coming from Balancer and using the number of Active requests in server as the load index (FBA),and Client Based Dispatching(CBD).