시퀀서

In the context of optimistic and zero-knowledge rollups, the sequencer acts as the central orchestrator responsible for [transaction ordering](/ko/terms/transaction-ordering) and state transitions off-chain. It receives a stream of user-submitted transactions (often via an RPC endpoint), validates their basic format and signature, and enqueues them into a mempool. The sequencer then deterministically orders these transactions, typically based on arrival time or a fee-market mechanism (e.g., EIP-1559-like structures if applicable), and executes them against the current rollup state. The result of this execution is a new state root, which is then committed to the layer-1 blockchain. Crucially, the sequencer batches multiple transactions into a single state transition. This batching is what enables the significant gas cost savings and throughput increases characteristic of rollups. For optimistic rollups, the sequencer constructs a proposed state transition and submits a transaction to the L1 containing the compressed transaction data and the resulting state root. A challenge period follows, during which anyone can submit a fraud proof if they detect an invalid state transition. For ZK-rollups, the sequencer not only orders and executes transactions but also generates a validity proof (e.g., a ZK-SNARK or ZK-STARK) that mathematically guarantees the correctness of the state transition. This proof, along with the transaction data and the new state root, is submitted to the L1 verifier contract. Decentralization of the sequencer is a key research area, with proposed solutions including shared sequencers, sequencer pools, and randomized leader election to mitigate censorship and single points of failure. The sequencer's internal logic often involves managing state forks, handling reorgs, and ensuring atomicity of batches.