Increasing the resilience of distributed and replicated database systems

This paper presents a new atomic commitment protocol, enhanced three phase commit (E3PC),that always allows a quorum in the system to make progress. P reviously suggested quorum-based protocols (e.g., the quorum-based three ph ase commit (3PC) (Skeen, 1982)), allow a quorum to make progress in case of one failure. If failures cascade, however, and the quorum in the system is "lost" (i.e., at a given rime no quorum component exists), a quorum can la ter become connected and still remain blocked. With our protocol, a connect ed quorum never blocks. E3PC is based on the quorum-based 3PC (Skeen. 1982) , and it does not require more time or communication than 3PC. We describe how this protocol can be exploited in a replicated database setting, making the database always available to a majority of the sites. (C) 1998 Academi c Press.