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 ZK proofZero-knowledge proof A cryptographic method that allows an individual to prove that a statement is true without conveying any additional information. This is useful for scaling blockchain networks through rollups, because it reduces the amount of information you have to provide to lower layers. 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 ZK-rollupZero-knowledge rollup An L2 scaling solution that uses a zero-knowledge proof as its validity proof to post data back to Ethereum. As compared to optimistic rollups, this validity proof allows for a more secure trust assumption and removes the need for a challenge period..

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 trace generator and conflator.

info

There is typically one sequencer instance per network. Although by applying a QBFTQuorum Byzantine Fault Tolerance (QBFT) The Byzantine-fault-tolerant consensus algorithm that Maru implements to let a validator set produce and finalize blocks, tolerating faulty validators in a 3f+1 validator set. design, Linea could adopt multiple sequencers in a decentralized configuration.

Transaction validity conditions

In addition to standard EVM validity checks (signature, nonce, balance, gas limits), the sequencer applies a Linea-specific profitability threshold during transaction pool admission and block-building selection. The threshold uses the same gas price calculation described in estimate gas costs, including the compressed transaction size, gas denominator, fixed/variable costs, and context-specific margin.

Transactions that do not meet the threshold can be rejected from the mempool or skipped during selection. This profitability check does not apply to sequencer-prioritized system transactions, including forced transactions.

See predictable pricing for how Linea's fee mechanism shapes the base fee, and Ethereum differences for a broader comparison.