区块链可扩展性研究：问题与方法

区块链技术作为分布式账本的关键技术之一，其在不依赖于任何第三方可信机构的前提下，解决开放网络中的信任问题，去中心化的特点使其有着广泛的应用前景，但面临着可扩展性不足的瓶颈.目前，区块链可扩展性的瓶颈主要体现在2个方面：性能效率低下、功能难以扩展.以比特币为例，从性能上讲，当前仅支持7笔/秒的交易吞吐量，显然无法满足现今数字支付的场景，也无法承载在数字支付领域外的其他应用.从功能上讲，当前不同区块链系统之间的资产或数据难以交互.在现实情况中，不同的区块链系统承载着不同的业务和需求.为此，需要实现链与链之间的交互，才能打通不同区块链之间的信息或价值通道，避免每一区块链成为信息或价值孤岛，并在此基础上实现价值互联网.区块链可扩展性的研究已经引起了学术界及产业界越来越多的关注，将从区块链性能提升及功能扩展2个角度出发，分别介绍区块链可扩展性领域的相关技术和研究进展，其中包括3类当前主流的、提升区块链交易吞吐量的方案：链下支付网络、Bitcoin-NG和分片机制；以及4类代表性的、实现区块链功能扩展的跨链互通技术.分析对比不同方案的特性、适合场景及可能存在的不足之处，并在此基础上给出进一步研究方向.

Research on Scalability of Blockchain Technology: Problems and Methods

As one of the key technologies of distributed ledgers, blockchain solves the trust problem in open network without relying on any trusted third party. Its decentralized feature makes it potential for a wide range of application scenarios. However, it still faces scalability problems. The bottleneck of blockchain scalability is mainly in two aspects: low efficiency and difficulty in functional extension. For instance, Bitcoin can only deal with 7 transactions per second averagely. Obviously, it cannot meet the requirement of current digital payment scenarios, nor can it be carried in other applications such as distributed storage and credit investigation service. On the other hand, the data or assets within different blockchains are difficult to interact with each other. This restricts the functional extension of blockchain system. In reality, there are a variety of blockchain systems which are specially devised for various functionalities or applications. Therefore, it is crucial to establish interaction channels among different blockchains to make them form the Internet of value. So far the research of blockchain scalability has attracted much attention from both academia and industry due to its importance. This paper introduces and analyzes the blockchain scalability related technologies from the aspects of improving efficiency and extending functionality of blockchain system, respectively. Firstly, we introduce three major schemes for performance enhancement of blockchain, including off-chain payment network, Bitcoin-NG and sharding mechanism; and four typical cross-chain approaches for blockchain functionality extension. Then we analyze the merits and demerits of each technology, based on which we give the challenges and suggestions for further research in blockchain scalability.