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Consensus-rollups (PoA)

A consensus-rollup, or proof of authority (PoA) rollup, is a type of rollup that relies on the assumption that there are enough honest operators to establish a consensus, without relying on a proof of correctness.

In consensus-rollups, operators take turns creating batches to be voted on by the other operators.

Finality

Consensus-rollups use the consensus established at the blockchain level. Finality of consensus-rollups (rollup-finality) is achieved when enough votes finalizing the consensus are included in a blockchain block.

Rollup-finality doesn't require a majority of votes. Rather, the proportion of nodes required to achieve rollup-finality is a configurable threshold, and is a trade-off between the expected proportion of Byzantine nodes (nodes that may present invalid information) and the target performance.

For example, in a network of 10 nodes:

  • If the system is configured to roll back (reject) a batch at 3 rejecting votes, 8 confirming votes are required to finalize a batch. This enforces safety: if 3 nodes disagree, the system stops.
  • If the system is configured to roll back a batch at 8 rejecting votes, 3 confirming votes are required to finalize a batch. This makes the system faster and less likely to stop. However, if 3 operators are malicious, they can collude to create an invalid rollup that they will accept, forcing the 7 other validators out.