Parallel Transaction Execution in Public Blockchain Systems

Abstract

Public blockchain systems like Ethereum and Bitcoin suffer from poor transaction throughput, leading to delayed transaction execution and high transaction fees. They execute transactions one by one, failing to extract inherent parallelism possible in executing the workload.

We present Block-X, a parallel transaction processing system with a serializable concurrency control that executes transactions in a block in a serializable order equivalent to the order of transactions in the block for public blockchains. It pre-executes transactions that are waiting to be added to a block. Through this pre-execution, Block-X estimates the keys a transaction wants to read or write. It uses this information to create a parallel execution schedule and run transactions optimistically in parallel following the schedule. It also uses the pre-execution to prefetch data that will be accessed during the critical path transaction execution. If a smart contract transaction accesses data outside of its initially estimated read-write set of keys, Block-X detects and resolves any potential conflicts. The final state is equivalent to the state produced after the sequential execution of transactions in the block order. Finally, Block-X also accelerates the process of validating blocks by providing the parallel execution schedule produced in the block execution step to validate transactions in parallel.

We implemented our system on Ethereum so it is compatible with EVM chains. Our evaluation demonstrates that Block-X achieves up to a 2.3× higher throughput than Ethereum. Moreover, our performance is comparable to other systems that perform pessimistic execution. These systems require predefined read-write set and reject transactions that use data outside of it.