Sequencer
What is it?
The sequencer is the heart of Linea's execution client, responsible for ordering, building, and executing blocks in a way that allows the subsequent zero-knowledge proof to be made.
The sequencer is not directly accessible from outside the network (to prevent DDOS attacks). Instead it’s connected to the RPC nodes via P2P.
What does it do?
The sequencer:
- Receives transactions from the network
- Orders and validates transactions
- Builds blocks according to Linea's rules
- Enforces transaction limits (trace counts, gas limits, calldata size)
- Ensures blocks fit within blob size constraints
- Executes those blocks
- Prepares certain data relating to the traces of that execution for the zero-knowledge prover
How does it do it?
The sequencer is a set of plugins that extends Linea's execution client Linea Besu. This implementation of the Besu execution client provides additional functionality to support Linea and its requirements as a zero-knowledge rollup.
Linea's sequencer takes transactions from the Linea memory pool, and builds them into blocks. Furthermore, it provides data to the coordinator, to ensure that blocks are made in such a way that they can be proven by the zero-knowledge prover, and that they are as compact as possible—doubly important in a situation where all data has to be written in tiny, costly pieces on Ethereum Mainnet. This is done specifically by subsystems within the sequencer: the traces generator and conflator.
There is typically one sequencer instance per network. Although by applying a Quorum-Based Byzantine Fault Tolerance (QBFT) design, Linea could adopt multiple sequencers in a decentralized configuration.