Impossibility Results in the Presence of Multiple Faulty Processes (Preliminary Version)

We investigate the impossibility of solving certain problems in an unreliable distributed system where multiple processes may fail. A necessary condition is provided for the solvability of problems in the presence of multiple faulty processes, and variants of problems which are unsolvable in the presence of a single faulty pro~~s (such as consensu.s, ehoo~ing a leader, r~g, matching) are shown to be solvable in the presence of t -1 faulty processes but not in the presence of t faulty processes for any t. In order to prove the impossibility result we u~e a novel technique: a contradiction is shown among a set of axioms which characterize any fault-tolerant protocol solving the problems we treat. These results generalize previously known impossibility results for completely asynchronous systems. T ec hn io n C om pu te r Sc ie nc e D ep ar tm en t T eh ni ca l R ep or t C S0 49 2 19 88