The State Machine Approach
The preceding intuitive discussion implies a simple technique for implementing a fault-tolerant service in terms of a State Machine:
- Place copies of the State Machine on multiple, independent servers.
- Receive client requests, interpreted as Inputs to the State Machine.
- Choose an ordering for the Inputs.
- Execute Inputs in the chosen order on each server.
- Respond to clients with the Output from the State Machine.
- Monitor replicas for differences in State or Output.
The remainder of this article develops the details of this technique.
- Step 1 and 2 are outside the scope of this article.
- Step 3 is the critical operation, see Ordering Inputs.
- Step 4 is covered by the State Machine Definition.
- Step 5, see Ordering Outputs.
- Step 6, see Auditing and Failure Detection.
The appendix contains discussion on typical extensions used in real-world systems such as Logging, Checkpoints, Reconfiguration, and State Transfer.
Read more about this topic: State Machine Replication
Famous quotes containing the words state, machine and/or approach:
“What thou art is mine;
Our state cannot be severed, we are one,
One flesh; to lose thee were to lose myself.”
—John Milton (1608–1674)
“He is no more than the chief officer of the people, appointed by the laws, and circumscribed with definite powers, to assist in working the great machine of government erected for their use, and consequently subject to their superintendence.”
—Thomas Jefferson (1743–1826)
“The modern world needs people with a complex identity who are intellectually autonomous and prepared to cope with uncertainty; who are able to tolerate ambiguity and not be driven by fear into a rigid, single-solution approach to problems, who are rational, foresightful and who look for facts; who can draw inferences and can control their behavior in the light of foreseen consequences, who are altruistic and enjoy doing for others, and who understand social forces and trends.”
—Robert Havighurst (20th century)