Avalanche validators poll a random handful of peers instead of the whole network

Why classical consensus does not scale

Traditional consensus protocols require every validator to hear from every other validator before a decision is made. That works fine for small networks, but message counts grow sharply as more nodes join, creating a scalability ceiling that limits how large a decentralised network can realistically get.

Avalanche (@avax) takes a different approach. Rather than requiring every validator to communicate with every other validator for every decision, a validator queries a small, randomly selected sample of peers and updates its preference based on responses. If a sufficient majority of the validators sampled reply with the same preferred transaction, that becomes the preferred choice of the validator that inquired. The node then adopts that preference going forward, and repeats the sampling process until validators queried reply the same way for a sufficient number of consecutive rounds.

Round after round, the network tips toward one answer. Repeated sampling causes the network to converge rapidly on a common result while limiting communication overhead.

Constant message counts and the Snowman protocol

The scalability benefit is concrete. Subsampling has low message overhead. It does not matter if there are twenty validators or two thousand validators: the number of consensus messages a node sends during a query remains constant. That is a meaningful departure from classical models, where message complexity scales with network size.

The protocol also conserves resources by design. It rests when there is nothing to decide, avoiding unnecessary computation during quiet periods.

For Avalanche's primary network, the linear-chain implementation of this approach is called Snowman. The Snowman Consensus Protocol is used by all three blockchains that form the Primary Network of Avalanche: the X-Chain, P-Chain, and C-Chain. Snowman is designed to cater to use cases that require a total and linear order of blocks, meaning transactions are processed in a strictly sequential manner, one after the other. The C-Chain supports smart contracts and DeFi applications using the Ethereum Virtual Machine, where most applications on Avalanche operate, and it uses the Snowman Consensus protocol, which processes transactions linearly.

Following the Cortina upgrade, the Primary Network uses Snowman across all three chains. The Ethereum consensus protocol on the C-Chain has been replaced with Snowman Consensus to enable lower block latency and higher throughput.

Sources
Avalanche Consensus, Avalanche Builder Hub (Official Docs)
Snowman Consensus, Avalanche Builder Hub (Official Docs)
Navigating the Avalanche: An Introduction to the Avalanche Network, Coin Metrics