Vegeta: Enabling Parallel Smart Contract Execution in Leaderless Blockchains

Consensus and smart contract execution play complementary roles in blockchain systems. Leaderless consensus, as a promising direction in the blockchain context, can better utilize the resources of each node and/or avoid incurring the extra burden of timing assumptions. As modern Byzantine-Fault Tolerant (BFT) consensus protocols can order several hundred thousand transactions per second, contract execution is becoming the performance bottleneck. Adding concurrency to contract execution is a natural way to boost its performance, but none of the existing frameworks is a perfect fit for leaderless consensus.

We propose speculate-order-replay, a generic framework tailored to leaderless consensus protocols. Our framework allows each proposer to (pre-)process transactions prior to consensus, better utilizing its computing resources. We instantiate the framework with a concrete concurrency control protocol Vegeta. Vegeta speculatively executes a series of transactions and analyzes their dependencies before consensus, and later deterministically replays the schedule. We ran experiments under the real-world Ethereum workload on 16-vCPU virtual machines. Our evaluation results show that Vegeta achieved up to 7.8× speedup compared to serial execution. When deployed on top of a leaderless consensus protocol with 10 nodes, Vegeta still achieved 6.9× speedup.