SoK: Applications of Sketches and Rollups in Blockchain Networks

Blockchain networks suffer from a critical scalability problem that is often expressed in two dimensions: the size of the network state and the computational overhead in processing transactions as part of the network update. This paper surveys two major families of solutions known as sketches and rollups that both rely on aggregation methods. Sketches are popular hash-based data structures used to represent a large amount of data while supporting particular queries such as on set membership, cardinality estimation and identification of large elements. Rollups play in a different form and refer to aggregation of the execution of multiple transactions to allow high transaction rates and low fees. The design of popular blockchain networks such as Bitcoin and Ethereum makes use of sketches for various tasks such as summarization of transaction blocks or declaring the interests of light nodes. In addition, rollups are implemented in several forms to allow high transaction rates through offloading parts of the execution out of the blockchain while keeping its security. This paper overviews the basics of sketches and rollups and provides a comprehensive survey on the wide range of existing applications of the two families in blockchains.