Sloppy Quorum Overlap

A Dynamo-style store runs N=3, W=2, R=2, so W + R > N. For key cart:88 the preference list is nodes A, B, C.

A network event isolates A and B. The coordinator does not fail the write: it takes the first N healthy nodes instead, so the write commits on C, D and E, where D and E carry hints saying the replicas belong to A and B.

The partition heals. Before hinted handoff has run, a client reads cart:88 with R=2 and the coordinator collects responses from A and B.

What does W + R > N guarantee here?

The guarantee only fails when W drops below a strict majority, and W=2 out of N=3 is already a majority

Nothing: two of the three write acknowledgements came from nodes outside the preference list, so a read quorum drawn from the preference list can miss the write entirely and return the pre-partition value

The overlap still holds, because a hinted replica counts as a member of the preference list for quorum purposes until the hint is delivered

The read returns both versions and the client reconciles them by vector clock, so the guarantee is preserved at the application layer