Can you keep a secret? A new protocol for sender-side enforcement of causal message delivery

A team of researchers including Yan Tong, Nathan Liittschwager, and Lindsey Kuper has introduced a new protocol named 'Cykas' (from "Can you keep a secret?") for enforcing causal message delivery in distributed systems. Causal delivery ensures messages are processed in an order that respects their cause-and-effect relationships, a critical property for consistency. Traditional sender-side enforcement avoids the metadata overhead of receiver-side methods but is overly conservative, often delaying message transmission unnecessarily. Cykas innovates by allowing messages to be sent eagerly while imposing specific constraints on their recipients, effectively reducing idle waiting time without sacrificing correctness.

The team implemented the Cykas protocol in Rust and rigorously verified its safety and liveness properties using the Stateright implementation-level model checker. This formal verification provides high confidence in the protocol's reliability. In practical experiments, Cykas demonstrated a clear performance advantage for applications involving long-running jobs. By permitting these jobs to start—and consequently finish—sooner, the protocol leads to a shorter overall execution time compared to the traditional sender-side approach. The research is slated for presentation at the Principles and Practice of Consistency for Distributed Data (PaPoC) conference in 2026.