Deferred Objects to Enhance Smart Contract Programming with Optimistic Parallel Execution

TL;DR

This paper introduces RapidLane, an extension for blockchain parallel execution engines that defers conflicting transaction computations, enabling higher throughput by turning some sequential workloads into parallel ones, demonstrated on the Aptos blockchain.

Contribution

The paper presents RapidLane, a novel extension allowing optimistic deferral of conflicting transaction computations, improving parallel execution in blockchains.

Findings

Up to 12x throughput increase on contended workloads

Effective integration with Block-STM and deployment on Aptos

Enables parallelization of certain sequential smart contract workloads

Abstract

One of the main bottlenecks of blockchains is smart contract execution. To increase throughput, modern blockchains try to execute transactions in parallel. Unfortunately, however, common blockchain use cases introduce read-write conflicts between transactions, forcing sequentiality. We propose RapidLane, an extension for parallel execution engines that allows the engine to capture computations in conflicting parts of transactions and defer their execution until a later time, sometimes optimistically predicting execution results. This technique, coupled with support for a new construct for smart contract languages, allows one to turn certain sequential workloads into parallelizable ones. We integrated RapidLane into Block-STM, a state-of-the-art parallel execution engine used by several blockchains in production, and deployed it on the Aptos blockchain. Our evaluation shows that on commonly contended workloads, such as peer-to-peer transfers with a single fee payer and NFT minting, RapidLane yields up to $12\times$ more throughput.