Definition and Uses of Rollup Design

Rollups are a relatively new L2 scalability solution implemented on Ethereum (and other chains to some limited extent) that enable scalability gains while providing (nearly) identical security guarantees as mainnet Ethereum.

The primary innovation of rollups is that they move computation off-chain while storing only the bare minimum of transaction data on-chain with negligible added trust assumptions. Rollups are

essentially alternate, “baby” blockchains that post their data to a primary blockchain, thus leveraging the consensus and data availability of that particular primary blockchain.

When rollup nodes synchronize the rollup chain, they employ the order imposed on the rollup blocks by the consensus and data availability layer. They finalize a rollup block if it is the first valid block at its height within the rollup to be published on the data availability layer—irrespective of whether the validity is checked directly (as with full nodes), or indirectly (as with light clients).