The reduced ceiling protocol for concurrency control in real-time databases with mixed transactions

This paper proposes a real-time concurrency control protocol called the red uced ceiling protocol (RCP) for real-time database systems consisting of ha rd and soft real-time transactions. The schedulability of hard real-time tr ansactions can be improved by bounding the blocking time from soft real-tim e transactions. Different concurrency control strategies are proposed to re solve data conflicts between different combinations of hard and soft real-t ime transactions, and the properties of the RCP schedules are shown. In the RCP, methodologies are proposed to reduce the number of aborts for soft re al-time transactions due to data conflicts with hard real-time transactions . Simulation experiments have been performed to study the performance of th e RCP as compared with the optimistic concurrency control with wait 50 (OCC wait-50) under different workloads of soft real-time transactions, various ratios of read/write operations and deadline constraints. It has been foun d that the RCP can not only guarantee the performance of hard real-time tra nsactions but also reduce the number of deadlines missed by the soft real-t ime transactions under all situations.