The Internet of Things (IoT) has been making people’s lives more efficient and more comfortable in the past years, and it is expected to get even better. This improvement may benefit from the use of blockchain to enhance security, scalability, reliability and auditability. Recently, different blockchain architectures were proposed to provide a solution that is better suited for IoT scenarios. One of them, called appendable-block blockchains, proposed a data structure that allows to include transactions in blocks that were already inserted in the blockchain. This approach allows appendable-block blockchains to manage large amounts of data produced by IoT devices through decoupled and appendable data structures. Nevertheless, consensus algorithms can impact throughput and latency in scenarios with large amount of produced transactions, since IoT devices can produce data very quickly (milliseconds) while these data might take some time to be included in a block (seconds). Consequently, it is important to understand the behaviour of different consensus algorithms over appendabble-block blockchain in these type of scenarios. Therefore, we adapted the appendable-block blockchain to use and compare the impact of different consensus algorithms: Practical Byzantine Fault Tolerance (PBFT), witness-based, delegated Byzantine Fault Tolerance (dBFT) and Proof-of-Work (PoW). The results show that both dBFT and PBFT can achieve fast consensus (< 150ms) in the context of appendable-block blockchains. We also present a discussion regarding attacks in each consensus algorithm to help one to choose the best solution (considering performance and security issues) for each scenario.

在过去的几年里，物联网 (IoT) 一直在让人们的生活更加高效和舒适，并且有望变得更好。这种改进可能受益于使用区块链来增强安全性、可扩展性、可靠性和可审计性。最近，提出了不同的区块链架构来提供更适合物联网场景的解决方案。其中一个称为可附加区块链，提出了一种数据结构，允许将交易包含在已经插入区块链中的区块中。这种方法允许可附加块区块链通过解耦和可附加的数据结构来管理物联网设备产生的大量数据。然而，在产生大量交易的场景中，共识算法会影响吞吐量和延迟，因为物联网设备可以非常快速地（毫秒）生成数据，而这些数据可能需要一些时间才能包含在一个块中（秒）。因此，在这些类型的场景中，了解不同共识算法在附加块区块链上的行为非常重要。因此，我们调整了可附加块区块链来使用和比较不同共识算法的影响：实用拜占庭容错（PBFT）、基于见证的、委托拜占庭容错（dBFT）和工作量证明（PoW）。结果表明，dBFT 和 PBFT 都可以在可附加块区块链的上下文中实现快速共识（< 150ms）。我们还讨论了每种共识算法中的攻击，以帮助人们为每种情况选择最佳解决方案（考虑性能和安全问题）。