Consensus in the presence of partial synchrony-英文文献.pdf

Consensus in the Presence of Partial Synchrony CYNTHIA DWORK AND NANCY LYNCH .MassachusettsInstitute of Technology, Cambridge, Massachusetts AND LARRY STOCKMEYER IBM Almaden Research Center, San Jose, California Abstract. The concept of partial synchrony in a distributed system is introduced. Partial synchrony lies between the cases of a synchronous system and an asynchronous system. In a synchronous system, there is a known fixed upper bound A on the time required for a messageto be sent from one processor to another and a known fixed upper bound % on the relative speeds of different processors. In an asynchronous system no fixed upper bounds A and @exist. In one version of partial synchrony, fixed bounds A and Cpexist, but they are not known a priori. The problem is to design protocols that work correctly in the partially synchronous system regardlessof the actual values of the bounds A and Cp.In another version of partial synchrony, the bounds are known, but are only guaranteed to hold starting at some unknown time T, and protocols must be designed to work correctly regardlessof when time T occurs. Fault-tolerant consensus protocols are given for various casesof partial synchrony and various fault models. Lower bounds that show in most casesthat our protocols are optimal with respect to the number of faults tolerated are also given. Our consensusprotocols for partially synchronous processors use new protocols for fault-tolerant “distributed clocks” that allow partially synchronous processorsto reach some approximately common notion of time. Categories and Subject Descriptors: C.2.4 [Computer-Communication Networks]: Distributed Systems- distribut