There are three questions to ask of any system: What abstraction does it implement? What is the design space for such an abstraction? Why is this abstraction useful? In a previous post, we examined the Paxos protocol and answered the first two questions. Paxos implements the abstraction of a Write-once Register (a WOR) using a combination of quorums and a two-phase locking protocol. As for the third question: Paxos is useful because it can be used to implement MultiPaxos (among other things)....
