Beyond 1-Safety and 2-Safety for replicated databases: Group-Safety

In this paper, we study the safety guarantees of group communication-based database replication techniques. We show that there is a model mismatch between group communication and database, and because of this, classical group communication systems cannot be used to build 2-safe database replication. We propose a new group communication primitive called \emph{end-to-end atomic broadcast} that solves the problem, i.e., can be used to implement 2-safe database replication. We also introduce a new safety criterion, called \emph{group-safety}, that has advantages both over 1-safety and 2-safety. Experimental results show the gain of efficiency of group-safety over lazy replication, which ensures only 1-safety.