Bottlenecks in Blockchain Consensus Protocols
This addresses scalability issues in blockchain permissioned systems for developers and researchers, but it is incremental as it analyzes existing protocols without proposing a new solution.
The paper studied the performance and scalability of four prominent Byzantine fault-tolerance consensus protocols (PBFT, Tendermint, HotStuff, and Streamlet) and found that they do not scale well with increasing validators due to communication complexity, with CPU costs limiting throughput and increasing latency.
Most of the Blockchain permissioned systems employ Byzantine fault-tolerance (BFT) consensus protocols to ensure that honest validators agree on the order for appending entries to their ledgers. In this paper, we study the performance and the scalability of prominent consensus protocols, namely PBFT, Tendermint, HotStuff, and Streamlet, both analytically via load formulas and practically via implementation and evaluation. Under identical conditions, we identify the bottlenecks of these consensus protocols and show that these protocols do not scale well as the number of validators increases. Our investigation points to the communication complexity as the culprit. Even when there is enough network bandwidth, the CPU cost of serialization and deserialization of the messages limits the throughput and increases the latency of the protocols. To alleviate the bottlenecks, the most useful techniques include reducing the communication complexity, rotating the hotspot of communications, and pipelining across consensus instances.