Sequencer of Layer 2

A program or node in a Layer 2 or Rollup blockchain network that orders transactions before they are processed or submitted to the Layer 1 blockchain.

What is a Sequencer?

In the context of Layer 2 (L2) scaling solutions, such as rollups (e.g., Optimistic Rollups or ZK-Rollups) on Ethereum, a sequencer is a specialized node or program responsible for receiving, ordering, and batching transactions before they are finalized or submitted to the Layer 1 (L1) blockchain. The sequencer plays a critical role in improving transaction throughput and reducing costs by processing transactions off-chain while maintaining the security and decentralization guarantees of the L1 blockchain.

The sequencer collects transactions from users, arranges them in a specific order, and creates a compressed batch or rollup of these transactions. This batch is then submitted to the L1 blockchain for validation and final settlement. In some L2 systems, a single sequencer is operated by the network’s developers or a designated entity, which can raise concerns about centralization, as the sequencer could potentially censor or reorder transactions. However, decentralized sequencer models and mechanisms like sequencer rotation or permissionless validation are being developed to address these concerns, ensuring greater fairness and trustlessness in L2 networks.