Towards Saving Blockchain Fees via Secure and Cost-Effective Batching of Smart-Contract Invocations

This paper presents iBatch, a middleware system running on top of an operational Ethereum network to enable secure batching of smart-contract invocations against an untrusted relay server off-chain. iBatch does so at a low overhead by validating the server's batched invocations in smart contracts without additional states of user nonces. The iBatch mechanism supports a variety of policies, ranging from conservative to aggressive batching, and can be configured adaptively to the current workloads. iBatch automatically rewrites smart contracts to integrate with legacy applications and support large-scale deployment. We built an evaluation platform for fast and cost-accurate transaction replaying and constructed real transaction benchmarks on popular Ethereum applications. With a functional prototype of iBatch, we conduct extensive cost evaluations, which shows iBatch saves 14.6%∼ 59.1% 14.6%∼59.1% Gas cost per invocation with a moderate 2-minute delay and 19.06\%∼ 31.52\%19.06%∼31.52% Ether cost per invocation with a delay of 0.26∼ 1.660.26∼1.66 blocks.