Tree topologies for causal message delivery.

Causal message delivery, i.e. the requirement that messages are delivered in an order respecting their causal (logical) dependencies, is often mandated in the distributed setting. So far, causal message delivery has been implemented by augmenting messages with meta data information that allows the receiver (or the platform) to re-order, and if necessary hold back, messages upon receipt before processing. We propose that causal message delivery can be achieved by construction, simply by organizing the nodes of the distributed application into a tree topology, and without the need for any meta data in the messages. We present our ideas informally through an example application and then develop a formal model and prove that causal message delivery is preserved in tree-based networks.