What Is Rollup?
Also known as: Rollup Chain, Optimistic Rollup, ZK-Rollup
In short
A rollup is a Layer 2 scaling solution that executes transactions in batches off the main blockchain, then publishes the compressed data and resulting state of those transactions to the main chain, inheriting its security from the main chain.
In a rollup, transactions are collected by an actor called a sequencer and processed in the rollup's own execution environment. The data of many transactions is compressed and sent in a single package to the main chain, for example Ethereum. Because the data is published on the main chain, anyone can reconstruct the rollup's state; because the main chain cost is shared among many users, transaction fees also fall.
There are two main types. Optimistic rollups assume transactions are valid by default and allow a period for an incorrect state to be challenged; Arbitrum and Optimism are in this group, and for this reason withdrawals directly to the main chain generally take about a week. ZK-rollups, on the other hand, produce a validity proof for each batch; zkSync and Starknet use this approach. Blob transactions (EIP-4844), which arrived with the Dencun upgrade in March 2024, noticeably reduced rollups' data publishing cost.
Rollups also have limits. Many rollups still depend on a single centralized sequencer; this sequencer can delay transactions or go down. Contract upgrade privileges being held by small groups and liquidity being fragmented across different rollups are also problems being worked on.
Last updated: · This content is for information purposes only and is not investment advice.