A Survey on Scalability and Privacy in Public Blockchains

: Public blockchains enable decentralized applications but continue to face persistent challenges in scalability, privacy, and decentralization. This survey employs a structured and comprehensive literature review of 114 peer-reviewed studies and reputable technical reports (2018–2025), selected using predefined search strings, inclusion/exclusion criteria, and a structured screening process, documented using a Literature selection flow diagram. Scalability techniques—including sharding, Layer 2 architectures (e.g., ZK-Rollups, Optimistic Rollups, commit chains), and privacy-enhancing technologies such as zero-knowledge proofs (ZKPs), trusted execution environments (TEEs), and protocol-native mixers—are critically analyzed. Standardized benchmarking evaluates throughput, latency, gas efficiency, and decentralization under consistent test conditions. A key contribution of this study is the first integrated, datadriven assessment of privacy–scalability trade-offs within the blockchain scalability trilemma framework. Empirical benchmarking indicates, for example, that zkSync Era demonstrates a theoretical throughput of ~2000 TPS but achieves ~0.52 TPS under measured network conditions, highlighting the computational overhead of ZKP generation. Hybrid architectures—such as zkPorter’s off-chain data availability combined with ZKPs or TEE-based routing— consistently outperform single-layer approaches in balancing performance, confidentiality, and trustlessness. Post-2021 advancements, including modular rollups, MEV-resistant sharding, and machine-learning-based load prediction, are reviewed alongside open challenges in standardized benchmarking, post-quantum privacy systems, and compliance-aware PETs. Future research directions emphasize cross-layer designs integrating ZKPs, dynamic sharding, and regulatory- ready privacy protocols to enable secure, scalable, and legally compliant blockchain ecosystems.