Satisfying timing constraints of real-time databases

Abstract

A real-time database has deadlines for processing transactions. Approximate query processing (AQP) has been presented as a strategy to satisfy these timing constraints by providing approximate answers to queries at the deadline instead of missing deadlines. In order to produce approximate answers, semantic information is maintained about the database and a computational overhead is required. In this paper the performance of AQP is examined to determine its effect on satisfying the timing constraints of real-time databases. Query and update transactions are modeled as periodic tasks with hard deadlines. A lock-based concurrency control is used and the effect of workload characteristics, such as the scheduling algorithm, the number of transactions and the percentage of update transactions, are examined. We compare the number of missed deadlines and approximate answers produced during AQP to the number of missed deadlines occurring during traditional query processing (TQP). Results demonstrate that despite the overhead, fewer deadlines are missed during approximate query processing than during TQP.