† Currently with Martis Oy, Finland. Proc. First Wokshop on Real-Time Databases (RTDB'96), March 7-8, 1996, Newport Beach, CA, U.S.A. The RAPID Case Study: Requirements for and the Design of a Fast-Response Database System Antoni Wolski Janne Karvonen Anton Puolakka † Technical Research Centre of Finland (VTT) VTT Information Technology P.O. Box 1201, 02044 VTT, Finland e-mail: <first name>.<last name>@vtt.fi WWW: http://www.vtt.fi/tte/projects/rapid Abstract Time-critical industrial applications represent a database requirement profile which is significantly different from that in traditional (business) database applications. Results of a corresponding needs survey performed among lead- ing developers of factory systems are presented in the paper. The requirements have paved way to the develop- ment of the RAPID system–a fast-response and active history database Client/Server system which has a unique assortment of temporal and active characteristics. Some of the most crucial design questions are discussed, including the choice of the process architecture and concurrency models, the temporal table model and the triggers seman- tics. 1 Introduction In a complex industrial installation (such as a paper mill, a power plant or a chemical process) a lot of data is pro- duced by sensors and the automatic control system. In order to post-process the data, the system has to cope with the following data characteristics: • the data assimilation rate may be as high as thou- sands measurements per second, • data sets are modeled as histories [Jen+94], • data changes require actions to be taken; an active behavior highly preferable, In [Dat94], systems of the above type are called ARCSs (Active Rapidly-Changing-Data Systems), and the corre- sponding database components—ARCS databases. An ARCS database incorporates concepts of temporal, active and real-time databases. In the RAPID project (1992–1995) we pursued ade- quate solutions for industrial ARCS databases. The work resulted in the construction of the RAPID Data Store System—a unorthodox Client/Server database system satisfying the most significant needs of certain industrial ARCS environments. In this paper, we summarize the needs surveys we performed in 1992 and 1993 (Section 2). In subsequent sections we discuss various design alternatives. Section 3 is devoted to issues of process architecture. In Section 4, we discuss multithreading and scheduling. Efficient implementation of temporal tables is dealt with in Section 5. New approaches to database trig- gers are presented in Section 6. In Section 7, we deal with selected issues related to the main-memory orientation in the database system design. A plan of future work con- cludes the paper. 2 Needs survey 2.1 Focus After the RAPID project had been started at VTT Information Technology in 1992, almost forty companies were surveyed with respect to special needs for database technology in the development of industrial data process- ing systems. Some of the companies later joined the pro- ject steering group and vastly contributed to the eventual shape of the RAPID software. The first step in the needs survey was to identify a prospective application area. An interesting observation was that, generally, the industrial partners were unwilling to consider using a real-time database to maintain the data