As Bitcoin and other cryptocurrencies become widely popular recently, the underlying concept—Blockchain—gets unprecedented attentions. One popular usage of Blockchain is a distributed replicated database. In this paper, we present initial studies on the challenges and opportunities of using Blockchain as a database for Internet-of-Things (IoT) applications. For IoT applications, latency is an important factor, whereas for application developers, consistency is an important property which specifies how the system orders the operations over blocks (that are stored in the Blockchain). However, consistency property of Blockchain-based database is not well studied, especially in the case when network is not synchronized and the system is dynamic—both are typical scenario in an IoT environment. Intuitively, Blockchain is designed to maintain a single ground truth—one can view the Blockchain itself as the order of the blocks that all participants should observe and respect. In most Blockchain designs, the participants will eventually converge to the same chain of blocks. However, there is very few study on the challenges of using Blockchains as a database in an IoT environment. This paper focuses on the enabling technology behind Bitcoin, Bitcoin Backbone Protocol (BBP). We first survey Blockchain-based IoT applications, and identify why it is necessary to use it as a database for IoT applications. Then we explore several reasonable consistency models for BBP-based database, and then show that such a database does not satisfy many consistency models under certain typical IoT environments. Moreover, we use simulation to study how network quality and system dynamic affect consistency. Finally, we propose a simple mechanism to make the BBP-based database satisfy both read-my-write and eventual consistency.

随着近来比特币和其他加密货币变得越来越流行，底层概念（区块链）得到了前所未有的关注。区块链的一种流行用法是分布式复制数据库。在本文中，我们对使用区块链作为物联网（IoT）应用程序数据库的挑战和机遇进行了初步研究。对于物联网应用程序，延迟是一个重要因素，而对于应用程序开发人员，一致性是一个重要属性，它指定系统如何按块（存储在区块链中）对操作进行排序。但是，基于区块链的数据库的一致性属性尚未得到很好的研究，特别是在网络不同步且系统运行正常的情况下。动态—都是IoT环境中的典型场景。直观地讲，区块链旨在维护一个基本事实，即人们可以将区块链本身视为所有参与者都应遵守和遵守的区块顺序。在大多数区块链设计中，参与者最终将融合到相同的区块链中。但是，关于在物联网环境中使用区块链作为数据库的挑战的研究很少。本文重点介绍比特币背后的支持技术，即比特币骨干网协议（BBP）。我们首先调查基于区块链的IoT应用程序，并确定为什么有必要将其用作IoT应用程序的数据库。然后，我们探索了基于BBP的数据库的几个合理的一致性模型，然后证明了这种数据库在某些典型的IoT环境下不能满足许多​​一致性模型。此外，我们使用仿真来研究网络质量和系统动态如何影响一致性。最后，我们提出了一种简单的机制来使基于BBP的数据库满足“自写自写”和最终的一致性。