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. Previously suggested quorum-based protocols (e.g., the quorum-based three phase 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 time no quorum component exists), a quorum can later become connected and still remain blocked. With our protocol, a connected 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.