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

TL;DR

Cykas is a new sender-side protocol for causal message delivery that enables eager sending and constrains recipients, improving performance for long-running distributed applications.

Contribution

We introduce Cykas, a novel sender-side causal delivery protocol that reduces conservativeness and enhances performance, validated through implementation and model checking.

Findings

Cykas allows earlier start and end of long-running jobs.

Cykas outperforms traditional sender-side approaches in execution time.

Implementation verified safety and liveness properties.

Abstract

Protocols for causal message delivery are widely used in distributed systems. Traditionally, causal delivery can be enforced either on the message sender's side or on the receiver's side. The traditional sender-side approach avoids the message metadata overhead of the receiver-side approach, but is more conservative than necessary. We present Cykas ("Can you keep a secret?"), a new protocol for sender-side enforcement of causal delivery that sidesteps the conservativeness of the traditional sender-side approach by allowing eager sending of messages and constraining the behavior of their recipients. We implemented the Cykas protocol in Rust and checked the safety and liveness of our implementation using the Stateright implementation-level model checker. Our experiments show that for applications involving long-running jobs, Cykas has a performance advantage: Cykas lets long-running jobs start (and end) earlier, leading to shorter overall execution time compared to the traditional sender-side approach.