A blockchain is designed to establish consistent and reliable agreements in an untrusted and decentralized environment. In addition, the blockchain enables transaction processing and the creation of smart contracts. It empowers end users to execute contracts without any intermediate entities. However, there are some issues when it comes to retrieving information, such as the state and history of smart contracts and regular transactions in the blockchain. For example, in a smart contract, user-defined data structures can be used to recall the state of the smart contract for a range query, which can decrease the general performance. In addition, an external database can be required to retrieve regular transactions for range queries, which increases management costs. To achieve this, we propose a new scheme that enables SQL query operations to retrieve a smart contract and regular transaction information within the blockchain system. To achieve this, we combine an embedded relational database with an Ethereum-based blockchain system to provide the SQL query. It enables range queries on smart contracts without requiring user-defined data structures and decreases management costs for regular transactions without any external database. We implement the proposed blockchain system on quorum, which is an Ethereum-based blockchain system. Also, we evaluate the proposed system using a synthetic benchmark. The performance of retrieving smart contract data is improved by up to approximately 22×, with low memory usage compared with the existing system. Moreover, the proposed system demonstrates a similar search performance to the existing system, even when considering external databases in regular transactions.

Application-specific blockchains are gaining popularity over general-purpose blockchains which require multiple services to share network resources. These blockchains adopt a modular architecture that allocates specific tasks to distinct layers, optimizing each layer for its designated role. While modular blockchains offer advantages, such as enhanced performance and flexibility, over general-purpose blockchains, they may exhibit low performance when attempting to achieve fast block finality. To address these issues, in this paper, we propose an efficient transaction processing scheme, Microcosm, to enhance the performance of the modular blockchain. Firstly, we propose fine-grained locking mechanisms to enable concurrent verification of unconfirmed transactions. Secondly, we enhance the efficiency of block execution by separating the transaction verification procedures and processing them in parallel. We implement Microcosm based on Tendermint and Cosmos-SDK, and our experimental results demonstrate that Microcosm provides a performance improvement by up to 2.3×, 1.7×, and 1.9× compared with a vanilla version of Cosmos, Osmosis, and Celestia known as some of the most popular modular blockchains, respectively.