Preventing orphan requests in the context of replicated invocation

In today´s systems, applications are composed from various components that may be located on different machines. The components (acting as servers) may have to collaborate in order to service a client request. More specifically, a client request to one component may trigger a request to another component. To ensure fault-tolerance, components are generally replicated. Replicated components lead to the problem of a replicated server invoking another replicated server. We call this the problem of replicated invocation. Replicated invocation has been considered in the context of deterministic servers. However, the problem is more difficult to address when servers are non-deterministic. In this context, work has been done to enforce deterministic execution. In this paper, we consider a different approach: instead of preventing non-deterministic execution of servers we discuss how to handle it. We present the problem of non-deterministic replicated invocation. Our solution then consists of sharing sufficient undo information among the replicas of the server invoking another server.