  Blockchain's decentralization, transparency, and tamper-resistance properties
have facilitated the system's use in various application fields. However, the
low throughput and high confirmation latency hinder the widespread adoption of
Blockchain. Many solutions have been proposed to address these issues,
including first-layer solutions (or on-chain solutions) and second-layer
solutions (or off-chain solutions). Among the proposed solutions, the
blockchain sharding system is the most scalable one, where the nodes in the
network are divided into several groups. The nodes in different shards work in
parallel to validate the transactions and add them to the blocks, and in such a
way, the throughput increases significantly. However, previous works have not
adequately summarized the latest achievements in blockchain sharding, nor have
they fully showcased its state-of-the-art. Our study provides a systemization
of knowledge of public blockchain sharding, including the core components of
sharding systems, challenges, limitations, and mechanisms of the latest
sharding protocols. We also compare their performance and discuss current
constraints and future research directions.
