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An Essay on Real-Time Databases

Data management in real-time systems has traditionally been implemented via applicationdependent designs. The main drawback of this approach is that, as the applications grow in complexity and amount of data, the code which deals with data management becomes increasingly difficult to develop and maintain. Real-time database systems are the most promising alternative to manage the data with a structured and systematic approach. Database systems have been successfully applied in many production systems. Many websites rely on conventional databases to provide a repository for data and to organize the retrieval and manipulation of data. However, this type of database is not suitable for applications with timing requirements (e.g. air traffic control, telecommunications and industrial control). It thus becomes interesting to apply techniques from the real-time systems research to provide timeliness in addition to the common features of database systems. The typical database design aims to provide a fast response time. Indeed, with suitable hardware resources it is possible to achieve impressive results. IBM presented in late 2006 a system capable of completing more than 4 million transactions per minute when running the TPC-C benchmark [15]. The same system would be even faster if advanced performance optimization techniques (such as indices) were allowed by the TPC-C specification. A fast database is, however, not necessarily a real-time database. For some applications the average transaction rate is not as important as completing each transaction before a certain deadline. For such applications the transaction rate is a parameter specified by the application designers. The real-time database then has to be designed in such a way that transactions meet their deadlines. Real-time databases thus have the requirement of ensuring transaction timeliness in addition to the well-known ACID properties. According to the ACID model the key transaction processing properties are atomicity, consistency, isolation and durability. A database management system which does not ensure all these properties (without a solid argumentation) should not be considered trustworthy.