A Recovery Model for Extended Real-Time Transactions

A central problem in the design of fault-tolerant realtime systems is that desirable fault-tolerance properties are usually realized by mechanisms that counteract realtime guarantees. A prominent example is the All-orNothing property (also known as failure atomicity) known from transactions. This property normally is realized by the means of isolation and roll-back recovery. However, isolation often unnecessarily decreases the degree of permitted concurrency and results in missed deadlines. Roll-back recovery implies that work is lost and has to be re-done, again leading to missed deadlines. So-called extended transaction models supersede isolation, but their recovery model induces an increased amount of roll-back recovery. In this paper, we present a fundamentally new recovery model to provide the All-orNothing property without requiring for isolation. Based on an active replication technique we provide a forward error recovery that avoids unnecessary roll-backs by replacing cancelled primary computations with hotstand-by alternate computations.