Quorum-based voting for replica control

The quorum-based voting for replica control is due to [Gifford, 1979][2] . Each copy of a replicated data item is assigned a vote. Each operation then has to obtain a read quorum (Vr) or a write quorum (Vw) to read or write a data item, respectively. If a given data item has a total of V votes, the quorums have to obey the following rules:

1. Vr + Vw > V
2. Vw > V/2

The first rule ensures that a data item is not read and written by two transactions concurrently. The second rule ensures that two write operations from two transactions cannot occur concurrently on the same data item. The two rules ensure that one-copy serializability is maintained.