Toward Massively Scalable Blockchains: A Survey of Layer-2 Innovations and Adaptive Sharding Frameworks

Blockchain systems are highly secure, transparent, and decentralized but have a limited transaction capacity and long confirmation time, which limits the applicability of blockchain systems to large scale. The largest popular blockchains include Bitcoin and Ethereum, whose throughput is less than 20 transactions per second, which is not enough to serve high demand applications. This survey provides a brief and methodical literature review of blockchain scalability systems, including Layer-2 scaling solutions, and adaptive sharding systems. This paper examine the architectural principles, performance advantages and security tradeoffs of Layer-2 systems, such as rollups, state channels, and sidechains, and Layer-1 sharding systems, such as static, dynamic and AI-assisted ones. Recent empirical investigations indicate that sharding and Layer-2 implementations are able to attain large throughput and latency reduction on top of monolithic architecture. This paper, describe the progress in standardization and outline the open issues in the cross-layer coordination, data availability, and security. The results of this survey can be used as a baseline in the creation of massively scalable, high-throughput decentralized systems.