Patterns of Distributed Systems

Chapter 8

Majority Quorum

Avoid two groups of servers making independent decisions by requiring majority for taking every decision.

Problem

Safety and Liveness

Liveness is the property of a system that says that the system always makes progress. Safety is the property that says that the system is always in the correct state. If we focus only on safety, then the system as a whole might not make progress. If we focus only on liveness, then safety might be compromised.

In a distributed system, whenever a server takes any action, it needs to ensure that in the event of a crash the results of the actions are available to the clients. This can be achieved by replicating the result to other servers in the cluster. But that leads to the question: ...