  With the advancement of blockchain systems, many recent research works have
proposed distributed ledger technology~(DLT) that employs Byzantine
fault-tolerant~(BFT) consensus protocols to decide which block to append next
to the ledger. Notably, BFT consensus can offer high performance, energy
efficiency, and provable correctness properties, and it is thus considered a
promising building block for creating highly resilient and performant
blockchain infrastructures. Yet, a major ongoing challenge is to make BFT
consensus applicable to large-scale environments. A large body of recent work
addresses this challenge by developing novel ideas to improve the scalability
of BFT consensus, thus opening the path for a new generation of BFT protocols
tailored to the needs of blockchain. In this survey, we create a
systematization of knowledge about the novel scalability-enhancing techniques
that state-of-the-art BFT consensus protocols use. For our comparison, we
closely analyze the efforts, assumptions, and trade-offs these protocols make.
