1 / 5 CRDTs, Gossip & Anti-Entropy

The Double Count

Three replicas share a G-counter. Replica A holds {A:5, B:2, C:0} and replica B holds {A:3, B:7, C:1}. A flaky link causes A to retransmit its state, so B merges the same incoming state twice. What does B hold afterwards?

A

{A:5, B:2, C:0}, because a state that is newer on one entry replaces the local state wholesale

B

{A:5, B:7, C:1}, because merge takes the element-wise maximum and is therefore idempotent

C

{A:8, B:9, C:1}, because merge adds the incoming vector entry by entry exactly once

D

{A:13, B:11, C:1}, because merge adds the incoming vector entry by entry for each copy