Techniques for implementing support middleware for the PSTR scheme for real-time object replication

The Primary-Shadow TMO Replication (PSTR) scheme is an active real-time object replication scheme formulated by the first author several years ago. PSTR is a powerful scheme in that it facilitates real-time forward recovery while prolonging the life-time of real-time application systems and it is applicable to a broad range of real-time distributed computing application systems. A middleware subsystem supporting the PSTR scheme has been designed as a part of the middleware architecture that is named ROAFTS and has been evolving since several years ago. ROAFTS is a middleware system which is layered above a commercial-off-the-shelf operating system kernel and functions as the core of a reliable execution engine for fault-tolerant distributed real-time applications. The applications supported by ROAFTS are structured as networks of real-time objects, named Time-triggered Message-triggered Objects (TMOs). The techniques for middleware-based implementation of the PSTR scheme have been improved in recent years. The ROAFTS middleware structure is reviewed first and then the improved implementation techniques are discussed. An analysis of the recovery time bounds achievable with the middleware prototype has also been conducted and some core results are presented.