CORBA (Common Object Request Broker Architecture) provides 16 Common Object Services for distributed application development, but none of them are fault tolerance related services. In this paper, we propose a replica...CORBA (Common Object Request Broker Architecture) provides 16 Common Object Services for distributed application development, but none of them are fault tolerance related services. In this paper, we propose a replicated object based Fault Tolerant Object Service (FTOS) for CORBA environment. Two fault tolerant mechanisms are provided in FTOS including dynamic voting mechanism and object replication mechanism. The dynamic voting mechanism uses majority voting strategy to ensure object state consistency in failure situations. The object replication mechanism can help system administrators to replicate and start up objects easily. Our implementation provides a library according to the style of COSS. With this library, programmers can develop distributed applications with fault tolerance capability very easily.展开更多
The phenomenal growth of the World Wide Web has brought huge increase in the traffic to the popular web sites. Long delays and denial of service experienced by the end-users, especially during the peak hours, continue...The phenomenal growth of the World Wide Web has brought huge increase in the traffic to the popular web sites. Long delays and denial of service experienced by the end-users, especially during the peak hours, continues to be the common problem while accessing popular sites. Replicating some of the objects at multiple sites in a distributed web-server environment is one of the possible solutions to improve the response time/latency. The decision of what and where to replicate requires solving a constraint optimization problem, which is NP-complete in gen- eral. In this paper, we consider the problem of placing copies of objects in a dis- tributed web server system to minimize the cost of serving read and write requests when the web servers have limited storage capacity. We formulate the problem as a 0-1 optimization problem and present a polynomial time greedy algorithm with backtracking to dynamically replicate objects at the appropriate sites to minimize a cost function. To reduce the solution search space, we present necessary condi- tions for a site to have a replica of an object in order to minimize the cost function. We present simulation results for a variety of problems to illustrate the accuracy and efficiency of the proposed algorithms and compare them with those of some well-known algorithms. The simulation results demonstrate the superiority of the proposed algorithms.展开更多
文摘CORBA (Common Object Request Broker Architecture) provides 16 Common Object Services for distributed application development, but none of them are fault tolerance related services. In this paper, we propose a replicated object based Fault Tolerant Object Service (FTOS) for CORBA environment. Two fault tolerant mechanisms are provided in FTOS including dynamic voting mechanism and object replication mechanism. The dynamic voting mechanism uses majority voting strategy to ensure object state consistency in failure situations. The object replication mechanism can help system administrators to replicate and start up objects easily. Our implementation provides a library according to the style of COSS. With this library, programmers can develop distributed applications with fault tolerance capability very easily.
文摘The phenomenal growth of the World Wide Web has brought huge increase in the traffic to the popular web sites. Long delays and denial of service experienced by the end-users, especially during the peak hours, continues to be the common problem while accessing popular sites. Replicating some of the objects at multiple sites in a distributed web-server environment is one of the possible solutions to improve the response time/latency. The decision of what and where to replicate requires solving a constraint optimization problem, which is NP-complete in gen- eral. In this paper, we consider the problem of placing copies of objects in a dis- tributed web server system to minimize the cost of serving read and write requests when the web servers have limited storage capacity. We formulate the problem as a 0-1 optimization problem and present a polynomial time greedy algorithm with backtracking to dynamically replicate objects at the appropriate sites to minimize a cost function. To reduce the solution search space, we present necessary condi- tions for a site to have a replica of an object in order to minimize the cost function. We present simulation results for a variety of problems to illustrate the accuracy and efficiency of the proposed algorithms and compare them with those of some well-known algorithms. The simulation results demonstrate the superiority of the proposed algorithms.
