摘要:区块链智能合约为不可信的分布式环境提供了去中心化的可信一致存储服 务。但是相比于传统中心化数据库，目前区块链平台的吞吐量的过于低下导致 它在多数应用中无法替代传统数据库。该性能问题部分源于目前的区块链不支 持区块交易的并发执行，因此通过设计并发控制算法来并发执行智能合约可以 提升区块链平台处理能力。在区块链网络中，验证者需要按照生产者采用的交 易顺序确定性地重新执行区块并产生一致的最终状态，因此传统DBMS中的并 发控制算法由于其结果的不确定性而无法直接应用在区块链中。 针对智能合约的确定性并发问题，本文通过引入多版本交易排序（MVTO） 的方法，提出了一个适用于区块链上的智能合约并发执行的并发框架。在该框 架中，矿工使用传统事务并发控制发现某冲突可串行化的调度，在执行中记录 交易写集以及调度的等价串行交易顺序到新区块中。其后，验证节点在执行该 区块前，利用区块中交易的写集和执行顺序为每个冲突的合约状态上预先构建 一个有序的版本链，静态地定义冲突操作之间的优先级关系。最后验证节点在 执行该区块时，基于上述版本链使用MVTO算法来实现以相同的等价串行交易 顺序确定性地并发执行该区块中的交易，从而达成分布式网络中合约状态一致 性的最终目的。 实验结果表明，相比于顺序执行，MVTO可以用3个线程的线程池执行实验 智能合约达到2.5倍左右的提升。

摘要:A Hyperledger Fabric is a popular permissioned blockchain platform and has great com- mercial application prospects. However, the limited transaction throughput of Hyperledger Fabric hampers its performance, especially when transactions with concurrency conflicts are initiated. In this paper, we focus on transactions with concurrency conflicts and propose solutions to optimize the performance of Hyperledger Fabric. Firstly, we propose a novel method LMLS to improve the Write-Write Conflict. This method introduces a lock mech- anism in the transaction flow to enable some conflicting transactions to be marked at the beginning of the transaction process. And indexes are added to conflicting transactions to optimize the storage of the ledger. Secondly, we propose a cache-based method to improve the Read-Write Conflict. The cache is used to speed up reading data, and a cache log is added to Hyperledger Fabric to ensure the data consistency. Extensive experiments demon- strate that the proposed novel methods can significantly increase transaction throughput in the case of concurrency conflicts, and maintain high efficiency in transactions without concurrency conflicts.

摘要:Popular blockchains such as Bitcoin or Ethereum provide a transaction isolation level of READ-COMMITTED. This provides difficulties when state changes many times per block interval. Hash-Mark-Set (HMS) alleviates this problem by enabling READ-UNCOMMITTED transactions for state variables. However, the current HMS implementation relies on a sequen- tial algorithm and is susceptible to redundant calculations. As modern processors rely more heavily on parallel algorithms to leverage multiple cores for speedup, sequential algorithms see less benefit from hardware improvements. This paper proposes a lock-free HMS to make use of thread-safe techniques and other optimizations to improve the performance of the HMS algorithm and reduce the latency of read-uncommitted state variable accesses. In our experiments, the proposed algorithm experiences an average 6.4x increase in performance up to 128 go-routines, and a maximum 11.1x increase.

摘要:Blockchain has attracted a broad range of interests from start-ups, enterprises and governments to build next generation applications in a decentralized manner. Similar to cloud platforms, a single blockchain-based system may need to serve multiple tenants simultaneously. However, design of multi-tenant blockchain-based systems is challenging to architects in terms of data and performance isolation, as well as scalability. First, tenants must not be able to read other tenants’ data and tenants with potentially higher workload should not affect read/write performance of other tenants. Second, multi-tenant blockchainbased systems usually require both scalability for each individual tenant and scalability with number of tenants. Therefore, in this paper, we propose a scalable platform architecture for multitenant blockchain-based systems to ensure data integrity while maintaining data privacy and performance isolation. In the proposed architecture, each tenant has an individual permissioned blockchain to maintain their own data and smart contracts. All tenant chains are anchored into a main chain, in a way that minimizes cost and load overheads. The proposed architecture has been implemented in a proof-of-concept prototype with our industry partner, Laava ID Pty Ltd (Laava). We evaluate our proposal in a three-fold way: fulfilment of the identified requirements, qualitative comparison with design alternatives, and quantitative analysis. The evaluation results show that the proposed architecture can achieve data integrity, performance isolation, data privacy, configuration flexibility, availability, cost efficiency and scalability.

摘要:Blockchain, or distributed ledger, provides a way to build various decentralized systems without relying on any single trusted party. This is especially attractive for smart contracts, that different parties do not need to trust each other to have a contract, and the distributed ledger can guarantee correct execution of the contract. Most existing distributed ledger based smart contract systems process smart contracts in a serial manner, i.e., all users have to run a contract before its result can be accepted by the system. Although this approach is easy to implement and manage, it is not scalable and greatly limits the system’s capability of handling a large number of smart contracts. In order to address this problem, we propose a scalable smart contract execution scheme that can run multiple smart contract in parallel to improve throughput of the system. Our scheme relies on two key techniques: a fair contract partition algorithm leveraging integer linear programming to partition a set of smart contracts into multiple subsets, and a random assignment protocol assigning subsets randomly to a subgroup of users. We prove that, our scheme is secure as long as more than 50% of the computational power is possessed by honest nodes. We then conduct experiments with data from existing smart contract system to evaluate the efficiency of our scheme. The results demonstrate that our approach is scalable and much more efficient than the existing smart contract platform.

摘要:Hyperledger Fabric is a distributed operating system for permissioned blockchains hosted by the Linux Foundation. It is the first truly extensible blockchain system for running distributed applications at enterprise grade scale. To achieve this, Hyperledger Fabric introduces a novel execute-order- validate blockchain architecture, allowing parallelization of transaction execution and validation. However, this raises the need for transaction isolation. Today transaction isolation is attained by locking the entire state database during simulation of transactions and database updates. This lock is one of the major performance bottlenecks as observed by previous work. This work presents a new lock-free approach for providing transaction isolation. It harnesses the already existing version- ing of key-value pairs in the database, used primarily for a read-write conflict detection during the validation phase, to create a version-based snapshot isolation. We further im- plement and evaluate our new approach. We show that our solution outperforms the current implementation by 8.1x and that it is comparable to the optimal solution where no isolation mechanism is applied.

摘要:Blockchain is well known as a decentralized and distributed public digital ledger, and is currently used by most cryptocurrencies to record transactions. One of the fundamental differences between blockchain and traditional distributed systems is that blockchain’s de- centralization relies on consensus protocols, such as proof of work (PoW). However, com- putation systems, such as application specific integrated circuit (ASIC) machines, have re- cently emerged that are specifically designed for PoW computation and may compromise a decentralized system within a short amount of time. These computationally resource- ful miners challenge the very nature of blockchain, with potentially serious consequences. Therefore, in this paper, we propose a general and flexible PoW method that enforces memory usage. Specifically, the proposed method blocks computationally resourceful min- ers and retains the previous design logic without requiring one to replace the original hash function. We also propose the notion of a memory intensive function (MIF) with a mem- ory usage parameter k ( k MIF ). Our scheme comprises three algorithms that construct a k MIF Hash by invoking any available hash function which is not k MIF to protect against ASICs, and then thwarts the pre-computation of hash results over a nonce. We then de- sign experiments to evaluate memory changes in these three algorithms, and the find- ings demonstrate that enforcing memory usage in a blockchain can be an effective defense against computationally resourceful miners.

摘要:Blockchain technologies are on the rise, and Hyper- ledger Fabric is one of the most popular permissioned blockchain platforms. In this paper, we re-architect the validation phase of Fabric based on our analysis from fine-grained breakdown of the validation phase’s latency. Our optimized validation phase uses a chaincode cache during validation of transactions, initiates state database reads in parallel with validation of transactions, and writes to the ledger and databases in parallel. Our experiments reveal performance improvements of 2×for CouchDB and 1.3× for LevelDB. Notably, our optimizations can be adopted in a future release of Hyperledger Fabric.

摘要:Bitcoin, as well as many of its successors, require the whole transaction record to be reliably acquired by all nodes to prevent double-spending. Recently, many blockchains have been proposed to achieve scale-out throughput by letting nodes only acquire a fraction of the whole transaction set. However, these schemes, e.g., sharding and off-chain techniques, suffer from a degradation in decentralization or the capacity of fault tolerance. In this paper, we show that the complete set of transactions is not a necessity for the prevention of double-spending if the properties of value transfers is fully explored. In other words, we show that a value-transfer ledger like Bitcoin has the potential to scale-out by its nature without sacrificing security or decentralization. Firstly, we give a formal definition for the value-transfer ledger and its distinct features from a generic database. Then, we introduce the blockchain structure with a shared main chain for consensus and an individual chain for each node for recording transactions. A locally executable validation scheme is proposed with uncompromising validity and consistency. A beneficial consequence of our design is that nodes will spontaneously try to reduce their transmission cost by only providing the transactions needed to show that their transactions are not double spend. As a result, the network is sharded as each node only acquires part of the transaction record and a scaleout throughput

摘要:Although the emergence of the programmable smart contract makes blockchain systems easily embrace a wider range of industrial areas, how to execute smart contracts efficiently becomes a big challenge nowadays. Due to the existence of Byzantine nodes, the mechanism of executing smart contracts is quite different from that in database systems, so that existing successful concurrency control protocols in database systems cannot be employed directly. Moreover, even though smart contract execution follows a two-phase style, i.e, the miner node executes a batch of smart contracts in the first phase and the validators replay them in the second phase, existing parallel solutions only focus on the optimization in the first phase, but not including the second phase. In this paper, we propose a novel efficient concurrency control scheme which is the first one to do optimization in both phases. Specifically, (i) in the first phase, we give a variant of OCC (Optimistic Concurrency Control) protocol based on batching feature to improve the concurrent execution efficiency for the miner and produce a schedule log with high parallelism for validators. Also, a graph partition algorithm is devised to divide the original schedule log into small pieces and further reduce the communication cost; and (ii) in the second phase, we give a deter- ministic OCC protocol to replay all smart contracts efficiently on multi-core validators where all cores can replay smart contracts independently. Theoretical analysis and extensive experimental results illustrate that the proposed scheme outperforms state-of- art solutions significantly.

摘要:A smart contract is an electronic transaction protocol intended to digitally facilitate, verify, or enforce the negotiation and execution of the terms of an underlying legal contract designed to fulfil common contractual conditions comprising payments, legal obligations, and enforcement without third parties. Thus, by following the traditional perception, smart contracts target to reduce transaction costs including arbitration and enforcement costs by realising trackable and irreversible transactions by using blockchain technology for distributed databases. However, the potential of smart contracts goes far beyond cost reductions by facilitating the entrepreneurial collaboration of cross-organisational businessprocesses that are characteristic for smart supply chains. A closer look to existing or ongoing smart contract projects reveals that the majority of smart-contract applications in business life are linked to supply chain management, Internet of Things and Industry 4.0 solutions. The author participated in several EU projects related to transnational entrepreneurial networks and smart supply chains. Thus, the paper discusses the research question of how and to which extent smart contracting and blockchain technology can facilitate the implementation of collaborative business structures for sustainable entrepreneurial activities in smart supply chains. The research is based on expert interviews, surveys and case studies, which took place in the context of the EU projects with a focus on the Baltic Sea Region.

摘要:Within the last few years, a countless number of blockchain systems have emerged on the market, each one claiming to revolutionize the way of distributed transaction processing in one way or the other. Many blockchain features, such as byzantine fault tolerance, are indeed valuable additions in modern environments. However, despite all the hype around the technology, many of the challenges that blockchain sys- tems have to face are fundamental transaction management problems. These are largely shared with traditional database systems, which have been around for decades already. These similarities become especially visible for systems, that blur the lines between blockchain systems and classical database systems. A great example of this is Hyperledger Fabric, an open-source permissioned blockchain system un- der development by IBM. By implementing parallel trans- action processing, Fabric’s workfow is highly motivated by optimistic concurrency control mechanisms in classical database systems. This raises two questions: (1) Which con- ceptual similarities and diferences do actually exist between a system such as Fabric and a classical distributed database system? (2) Is it possible to improve on the performance of Fabric by transitioning technology from the database world to blockchains and thus blurring the lines between these two types of systems even further? To tackle these questions, we frst explore Fabric from the perspective of database research, where we observe weaknesses in the transaction pipeline. We then solve these issues by transitioning well-understood database concepts to Fabric, namely transaction reordering as well as early transaction abort. Our experimental eval- uation under the Smallbank benchmark as well as under a custom workload shows that our improved version Fabric++ signifcantly increases the throughput of successful transac- tions over the vanilla version by up to a factor of 12x, while decreasing the average latency to almost half.

摘要:TheriseofsmartcontractsystemssuchasEthereum has resulted in a proliferation of blockchain-based decentralized applications including applications that store and manage a wide range of data. Current smart contracts are designed to be executed solely by miners and are revealed entirely on-chain, resulting in reduced scalability and privacy. In this paper, we discuss that scalability and privacy of smart contracts can be enhanced by splitting a given contract into an off-chain contract and an on-chain contract. Specifically, functions of the contract that involve high-cost computation or sensitive information can be split and included as the off-chain contract, that is signed and executed by only the interested participants. The proposed approach allows the participants to reach unanimous agreement off-chain when all of them are honest, allowing computing resources of miners to be saved and content of the off-chain contract to be hidden from the public. In case of a dispute caused by any dishonest participants, a signed copy of the offchain contract can be revealed so that a verified instance can be created to make miners enforce the true execution result. Thus, honest participants have the ability to redress and penalize any fraudulent or dishonest behavior, which incentivizes all participants to honestly follow the agreed off-chain contract. We discuss techniques for splitting a contract into a pair of on/off-chain contracts and propose a mechanism to address the challenges of handling dishonest participants in the system. Our implementation and evaluation of the proposed approach using an example smart contract demonstrate the effectiveness of the proposed approach in Ethereum.

摘要:比特币是中本聪（Nakamoto）于2008年提出的数字货币，它具有去中心化、跨国界和发行总量 固定等特性，现在已经成为使用最广泛的数字货币之一．然而，比特币设计初期的一些人为限制，导致现 有网络处理交易的速率十分有限，最近交易处理能力已经接近上限，交易确认时间显著增加．这不仅严 重影响比特币的使用体验，进而限制使用范围，而且对比特币的设计提出更高的要求．针对比特币所面 临的交易处理性能挑战，以提升区块链容量为目标对比特币展开深入研究．首先，分析比特币当前网络 状态，根据比特币交易数据，统计交易延迟情况；其次，针对链上扩容方案，分析可行性，研究扩容效果；再次，针对链下扩容方案，分析作用原理，研究扩容效果；最后，分析链上／链下扩容方案优缺点，提出适 应社区的可行的比特币扩容路线方案．最新比特币扩容的进展进一步证明了我们结论的正确性。

摘要:Blockchain is very important in finance field and electronic business field, so many researchers are attracted to study the technologies of blockchain. Since the transactions in blockchain takes much time, and they make the blockchain poor efficiency, business processes across organizations require the transactions as soon as possible. Concurrency is attracted much attention and is very important in blockchain field. In this paper, a novel decentralized blockchain network model with high concurrency is proposed. First, the idea of the proposed model is stated. Second, the high concurrency blockchain network model is proposed. Third, the corresponding algorithms are designed according to the proposed model. Furthermore, the experiment is conduced and the results show that proposed model works well.