Quorum-Based Multi-Invocation Model for Replicated Objects

In distributed systems, resources like databases are abstracted to be objects in order to increase the interoperability. Objects are replicated to make a system more reliable and available. In object-based systems, methods are invoked in a nested manner, i.e. methodsnamed invokees are invoked in another method named invoker. How to invoke methods on multiple replicas in the nested manner is discussed here. In this paper, methods are invoked on a quorum number of replicas of objects. Suppose each instance of a method t on multiple replicas of an object x invokes a method u on replicas in a quorum of another object y. Here, the method u is redundantly invoked, i.e. the same method is invoked many times on some replicas of the object y. This is redundant invocation. If each instance of the invoker method t invokes a method u on replicas in its own quorum of the object y, more number of replicas are manipulated by the method u than the quorum number. This is quorum expansion. A quorum-based multi-invocation (QMI) protocol is discussed where each of the multiple invokers invokes a method on the multiple replicas, and each of the invokee methods sends a response to multiple invokers without redundant invocation and quorum expansion. In addition, responses of the method are also sent to a quorum number of invokers. Even if some numbers of invoker and invokee replicas are faulty, every method can be surely performed on at least one operational replica, every operational invokee replica can receive at least one method request, and every operational invoker replica can receive at least one response. The QMI protocol is evaluated on how many replicas are manipulated and requests are issued in the presence of replica faults compared with the traditional primary–secondary replication.