State Machine Replication
For the subsequent discussion a State Machine will be defined as the following tuple of values (See also Mealy machine and Moore Machine):
- A set of States
- A set of Inputs
- A set of Outputs
- A transition function (Input x State -> State)
- An output function (Input x State -> Output)
- A distinguished State called Start.
A State Machine begins at the State labeled Start. Each Input received is passed through the transition and output function to produce a new State and an Output. The State is held stable until a new Input is received, while the Output is communicated to the appropriate receiver.
It should be clear that any algorithm can be implemented using this model if driven by an appropriate Input stream. In particular, this discussion requires a State Machine to have the following property:
- Deterministic:
- Multiple copies of the same State Machine begun in the Start state, and receiving the same Inputs in the same order will arrive at the same State having generated the same Outputs.
Read more about State Machine Replication: The State Machine Approach, Historical Background
Famous quotes containing the words state and/or machine:
“They that have grown old in a single state are generally found to be morose, fretful and captious; tenacious of their own practices and maxims; soon offended by contradiction or negligence; and impatient of any association but with those that will watch their nod, and submit themselves to unlimited authority.”
—Samuel Johnson (1709–1784)
“The American people is out to get the kaiser. We are bending every nerve and every energy towards that end; anybody who gets in the way of the great machine the energy and devotion of a hundred million patriots is building towards the stainless purpose of saving civilization from the Huns will be mashed like a fly. I’m surprised that a collegebred man like you hasn’t more sense. Don’t monkey with the buzzsaw.”
—John Dos Passos (1896–1970)