SoK: Compression in Rollups

Abstract

A rollup is a scaling solution built on top of an existing blockchain. Rollups separate execution from consensus, but are required to post the data used for state updates to the underlying blockchain. This data is required to ensure that execution of state updates are performed correctly. As writing data to a public blockchain is not free, rollups are incentivized to minimize the amount of data they post on-chain. Rollups therefore aggregate and compress the data used for executions in order to save on fees associated with writing data to the blockchain. In this work, we explore the methods for posting data on-chain and the compression techniques used by real-world rollups. We explore differences in implementations and contrast the approaches used by both optimistic and zero-knowledge rollups. We also explore approaches which enable domain-specific compression, consider upcoming changes to data storage on Ethereum, and suggest improvements for rollup compression.