Immediate ordered service in distributed systems

A technique is presented by which a centralized service facility in a distributed system can honor client requests in the global order in which those requests were made. Unlike traditional approaches to this problem, the server provides immediate service to its clients. Immediate service requires that, upon receipt of a request which is the oldest unserved message, the server must grant the service immediately. No additional message passing may be used by the server in order to serve that request. The approach requires that certain information be appended to every message in the system. This piggybacked information allows the server to infer the order in which service should be granted to arriving request messages. Increased message length is thus explicitly traded for fewer messages and faster response to requests at the server. That overhead is proportional to the number of processors in the system. In time-critical distributed applications immediate service offers a means by which service response time can be substantially reduced. It is argued that, under certain reasonable assumptions about the network and process behavior, immediate service can outperform the logical timestamp approach for very large systems (and certainly for small systems).<
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