  As transaction fees skyrocket today, blockchains become increasingly
expensive, hurting their adoption in broader applications.
  This work tackles the saving of transaction fees for economic blockchain
applications. The key insight is that other than the existing "default" mode to
execute application logic fully on-chain, i.e., in smart contracts, and in fine
granularity, i.e., user request per transaction, there are alternative
execution modes with advantages in cost-effectiveness.
  On Ethereum, we propose a holistic middleware platform supporting flexible
and secure transaction executions, including off-chain states and batching of
user requests. Furthermore, we propose control-plane schemes to adapt the
execution mode to the current workload for optimal runtime cost.
  We present a case study on the institutional accounts (e.g., coinbase.com)
intensively sending Ether on Ethereum blockchains. By collecting real-life
transactions, we construct workload benchmarks and show that our work saves 18%
~ 47% per invocation than the default baseline while introducing 1.81 ~ 16.59
blocks delay.
