Understanding Scalability Issues in Sharded Blockchains

Since the release of Bitcoin in 2008, cryptocurrencies have attracted attention from academia, government, and enterprises. Blockchain, the backbone ledger in many cryptocurrencies, has shown its potential to be a data structure carrying information over the network securely without the need for a centralized trust party. In this thesis, I delve into the consensus protocols used in permissioned blockchains and analyze the sharding technique that aims to improve the scalability in blockchain systems. I discuss a permissioned sharded blockchain that I use to examine different methods to interleave blocks, referred to as strong temporal coupling and weak temporal coupling. I provide empirical experiments to show the roles of lightweight nodes in solving the scalability issues in sharded blockchain systems. The results suggest that the weak temporal coupling method performs worse than the strong temporal coupling method and is more susceptible to an increase in network latency. The results also show the importance of separating the roles of nodes and adding lightweight nodes to improve the performance and scalability of sharded blockchain systems