What is Sequencer?
A sequencer is the component of a Layer 2 rollup that receives transactions, orders them, executes them, and produces the resulting state updates — the central coordinator of rollup transaction processing.
WHY IT MATTERS
Sequencers are the engines of rollups. They receive incoming transactions, determine execution order, process them, and produce state updates that are eventually posted to L1. Currently, most rollup sequencers are operated by the rollup team (centralized).
Centralized sequencers offer: fast confirmation (instant soft confirmation before L1 posting), censorship risk (the operator can exclude transactions), and MEV extraction ability (the operator controls ordering).
Decentralizing sequencers is a top priority for the rollup ecosystem. Approaches include: shared sequencing (multiple rollups share a sequencer), leader rotation (validators take turns), and based sequencing (using L1 for ordering).