How does Mnesia keep replicated tables consistent across nodes?

Every write inside a transaction on a replicated table is propagated to all nodes holding a copy as part of that same transaction's commit, coordinated through a two-phase commit protocol: a coordinating node asks each replica to prepare the write, and only tells them all to actually commit once every replica has confirmed it can.

sequenceDiagram
    participant Coord
    participant NodeA
    participant NodeB
    Coord->>NodeA: prepare write
    Coord->>NodeB: prepare write
    NodeA-->>Coord: ready
    NodeB-->>Coord: ready
    Coord->>NodeA: commit
    Coord->>NodeB: commit

If any replica can't prepare (it's unreachable, or has a conflicting lock), the whole transaction aborts on every node rather than applying on some and not others — this is precisely what gives Mnesia its all-or-nothing consistency guarantee across a cluster rather than just within a single node.

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