Consensus: Power and Implementability Limit in Crash-Prone Asynchronous Systems
This chapter first presents the TO-broadcast communication abstraction, the state machine replication paradigm, and the ledger object, and shows that they all are computationally equivalent. It also shows that any object (abstraction) defined by a sequential specification (sequential state machine, or ledger) can be implemented in CAMPn,t[CONS] (CAMPn,t\([\emptyset]\) enriched with consensus). In this sense the consensus agreement abstraction is universal. It provides the computability power needed to implement any object – defined by a sequential specification – despite asynchrony and the crash of any minority of processes.
KeywordsConsensus abstraction Consensus number FLP Impossibility Non-determinism Process crash Sequential specification State machine replication Total order broadcast Universal object (abstraction)
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