Scalable blockchains — A systematic review

Blockchains are a key disruptive technology of recent times with applications across several application domains such as finance, supply chain, healthcare and Industry 4.0. With growing application types, scalability of blockchains has emerged as a key challenge in achieving the potential of this technology. This paper attempts to outline this challenge for blockchains as follows. It highlights blockchain scalability as a composite concept which can be interpreted in various ways i.e. expanding the number of participants of the network, or enhancing capabilities of the participants (such as processing, memory, storage or an efficient consensus strategy) to minimize the scalability overhead. Further, it presents a first thorough systemic study of existing efforts to achieve blockchain scalability with respect to; (i) innovative methods and mechanisms to strengthen blockchain's capabilities with respect to scalability, (ii) approaches leveraging blockchains to achieve scalable applications, and (iii) efforts analyzing blockchain solutions with respect to scalability. Through a critical analysis of existing literature, the paper identifies contributions as well as open challenges which can help research community to advance knowledge within this domain.