Combining optimistic and pessimistic replication

Abstract

This paper presents a concept of combining pessimistic and optimistic approach to replication. Optimistic replication allows for tentative system states, which increases availability and efficiency, but makes behaviour of the system less predictable, even if some operations seem completed. To enable more stable results, pessimistic and optimistic modes of operations are distinguished. Operations issued in the optimistic mode accept or produce tentative states, while operations issued in the pessimistic mode appear as completed in a stable state, termed committed. Orthogonally, to refine expectations of the results, modifications are specified as either synchronous or asynchronous, and reads as either synchronised or immediate. © 2012 Springer-Verlag.