Nonblocking and orphan-free message logging protocols

Currently existing message logging protocols demonstrate a classic pessimistic vs. optimistic tradeoff. It is shown that the optimistic-pessimistic tradeoff is not inherent to the problem of message logging. The authors construct a message-logging protocol that has the positive features of both optimistic and pessimistic protocols: the protocol prevents orphans and allows simple failure recovery; however, it requires no blocking in failure-free runs. Furthermore, this protocol does not introduce any additional message overhead as compared to one implemented for a system in which messages may be lost but processes do not crash.