Abstract
Blockchain (e.g., Bitcoin and Ethereum) has drawn much attention and has been widely-deployed in recent years. However, blockchain scalability is emerging as a challenging issue. This paper outlines the existing solutions to blockchain scalability, which can be classified into two categories: first layer and second layer solutions. First layer solutions propose modifications to the blockchain (i.e., changing the blockchain structure, such as block size) while second layer solutions propose mechanisms that are implemented outside of the blockchain. In particular, we focus on sharding as a promising first layer solution to the scalability issue; the basic idea behind sharding is to divide the blockchain network into multiple committees, each processing a separate set of transactions. More specifically, (a) we propose a taxonomy based on committee formation and intra-committee consensus; and (b) we compare the main existing sharding-based blockchain protocols. We also present a performance-based comparative analysis (i.e., throughput and latency), of the advantages, and disadvantages in existing scalability solutions.
Highlights
In recent years, Blockchain technology has been widely used in almost all industry segments, including the healthcare sector [24], [25], cryptocurrencies [1], [17], artificial intelligence [22], [23], the government sector [28], [29], internet of things [26], [27], and others [30]
The scalability trilemma is well-known in blockchain; it was first described by Vitalik Buterin, the cofounder of Ethereum [38]
We present a taxonomy in which we classify shardingbased blockchain protocols based on committee formation and intra-committee consensus; we analyze the security of these protocols by computing the failure probability for one committee and for each epoch
Summary
Blockchain technology has been widely used in almost all industry segments, including the healthcare sector [24], [25], cryptocurrencies [1], [17], artificial intelligence [22], [23], the government sector [28], [29], internet of things [26], [27], and others [30]. Every one of these segments benefit from Blockchain’s transparent, decentralized, immutable, and fully distributed peer-to-peer architecture that records digital assets (e.g., transactions) Despite these attractive characteristics, one of the key limitations of blockchain is scalability; the number of transactions that can be processed per second is small and insufficient (e.g., up to 7 for Bitcoin [1] and 15 for Ethereum [17]). We present a detailed comparison of existing solutions of scalability based on their performances (i.e., throughput, latency), advantages, and disadvantages. A. SCALABILITY The objective of existing blockchain scalability solutions is to process a high number of transactions per second (i.e., throughput) without sacrificing security and decentralization [45], [46].
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