Steelhead: Interleaving Partially Synchronous and Asynchronous Commit Rules on a Shared DAG
Steelhead interleaves partially synchronous and asynchronous DAG commit rules and adapts without extra messages.
Steelhead is a dual-mode consensus mechanism that applies an asynchronous commit rule every k-th DAG round and a partially synchronous rule otherwise. Validators periodically replay the committed DAG, adopt the period with the fewest expected message delays, and fall back to k=1 if output stalls, while the asynchronous rule on coin rounds preserves liveness. It sends no messages beyond DAG blocks. Instantiations with Mysticeti and Mahi-Mahi at n at least 3f+1, and BlueBottle variants at n at least 5f+1, have safety and liveness proofs including Lean 4 mechanization; simulations match the partially synchronous protocol on a healthy network and stay near the asynchronous one when that protocol stalls.
- Every k-th round uses an asynchronous rule with a post-vote common coin.
- No extra messages are sent to agree on the operating period.
- Instantiated with Mysticeti, Mahi-Mahi, and BlueBottle variants.
- Lean 4 proofs cover safety and liveness.
Full article214 words · extracted from arxiv.org · click to collapse
Dual-mode consensus protocols are fast when the network is partially synchronous and remain live under asynchrony. We introduce Steelhead, a dual-mode mechanism that composes a partially synchronous and an asynchronous commit rule over one DAG: every k-th round is decided by the asynchronous rule, whose leader a common coin reveals after the votes, and all other rounds by the partially synchronous rule. Every interval, validators replay the committed DAG under each candidate period, adopt the one with the fewest expected message delays, and fall back to k = 1 when the output stalls; the asynchronous rule applied to the coin rounds alone keeps the protocol live. Steelhead sends no message beyond the DAG's blocks, not even to agree on the period, and opens a coin only on the rounds that need a hidden leader. It is generic over pairs of DAG commit rules that share a committee; we instantiate it with Mysticeti and Mahi-Mahi at n >= 3f+1 and with the two variants of BlueBottle at n >= 5f+1. We prove it safe and live, and provide mechanized proofs in Lean 4. In simulation, Steelhead matches the partially synchronous protocol in a healthy network, stays close to the asynchronous one when network conditions stall the partially synchronous one, and adapts quickly in both directions.
Text extracted automatically; images, tables and formatting may be missing. Original: https://arxiv.org/abs/2609.30163