Law
Quorum intersection
R + W > N buys overlap. Overlap alone gives neither linearizability nor even monotonic reads.
- Copies
- copies of each item
- Write quorum
- replicas that must acknowledge a write
- Read quorum
- replicas a read asks
Worked examples, recomputed
Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.
Where it appears
Each mechanism states it in its own names. The general symbol each name stands for is shown with it.
- Consistency & Isolation Models
When many users, many objects and many copies exist at once, which histories does the system promise never to show, and who writes the code for the histories it does show?
- Distributed Systems Coordination
Who is allowed to decide, and how does everyone else learn the decision without asking?
- Fault Tolerance & Delivery Semantics
What is the cheapest thing that can be safely done twice?