Permissioned Blockchain Through the Looking Glass: Architectural and Implementation Lessons Learned
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Since the inception of Bitcoin, the distributed and database community has shown interest in the design of efficient blockchain systems. At the core of any blockchain application is a Byzantine-Fault Tolerant (BFT) protocol that helps a set of replicas reach an agreement on the order of a client request. Initial blockchain applications (like Bitcoin) attain very low throughput and are computationally expensive. Hence, researchers moved towards the design of permissioned blockchain systems that employ classical BFT protocols, such as PBFT, to reach consensus. However, existing permissioned blockchain systems still attain low throughputs (of the order 10K txns/s). As a result, existing works blame this low throughput on the associated BFT protocol and expend resources in developing optimizes protocols. We believe such blames only depict a one-sided story. In specific, we raise a simple question: can a well-crafted system based on a classical BFT protocol outperform a modern protocol? We show that designing such a well-crafted system is possible and illustrate cases where a three-phase protocol can outperform a single-phase protocol. Further, we dissect a permissioned blockchain system and state several factors that affect its performance. We also design a high-throughput yielding permissioned blockchain system, ResilientDB, that employs parallel pipelines to balance tasks at a replica, and provides guidelines for future designs.
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