author: Sjoerd Wels
title: Guaranteed-TX: The exploration of a guaranteed cross-shard transaction execution protocol for Ethereum 2.0
keywords: software engineering, block chain, ethereum
topics: Case studies and Applications , Dependability, security and performance , Software Technology
committee: Ansgar Fehnker ,
Maarten Everts
end: October 2019


A major bottleneck of the state-of-the-art distributed ledgers is the limited transaction throughput. Existing ledgers lack scalability and are unable to process transactions at the speed of centralised systems. One technique used by Ethereum 2.0 to overcome these performance and scalability limitations is sharding. With sharding, the computational work is partitioned among multiple, smaller groups of validators referred to as shards. These shards operate in parallel to increase the overall transaction throughput while minimising the communication, computation and storage requirements per node. However, the interoperability between shards is yet very limited. It can take several minutes before a shard is allowed to process a cross-shard transaction while there is no guarantee that a cross-shard transaction will be processed at all. Without interoperability improvements, sharding will only benefit smart contract applications that run within a single shard.

In this study we propose Guaranteed-TX, a guaranteed cross-shard transaction execution protocol for Ethereum 2.0. Guaranteed-TX allows shards to process cross-shard transactions before being finalised in the block it was created - a property called optimistic execution - which significantly improves cross-shard transaction latencies. In addition, it provides economic guarantees that all cross-shard transaction will eventually be processed.