The Definitive Guide to Sequencing

Shared Sequencing is explained here through the role of the Sequencer in optimistic rollups, which the author argues exists to reduce user transaction costs while concentrating ordering control in one semi-trusted party. The Sequencer batches many user transactions off-chain and commits them to the host chain in a single transaction, so per-transaction costs are amortized, whereas self-ordered transactions on Ethereum carry a 21,000 gas fee each. The text states that the Sequencer can exclude or reorder transactions and extract MEV, and that Proposers, who are separate from Sequencers, compute and attest to the resulting rollup state.