It is challenging to manage the performance of real-time databases (RTDBs) that are often used in data-intensive real-time applications such as agile manufacturing and target tracking. Feedback control has recently been considered a promising approach to enabling reliable real-time data service. However, most existing work on feedback control of RTDB performance is not based on a RTDB-specific control model, which is critical for closed-loop system design. To address this problem, we design a novel RTDB model that can capture RTDB dynamics by modeling the relation between the total arrival rate (sum of the transaction arrival rate and restart rate) and utilization via a difference equation. Based on the model, we design and tune a utilization controller to compute the total arrival rate adjustment needed to support the desired average/transient utilization. We also design a QoS management scheme and admission control technique that can judiciously adapt the transaction QoS and arrival rate in a RTDB, if necessary, to support the desired utilization, while enhancing the success ratio. In a simulation study, we show that our approach can support the desired average/transient utilization for a range of transaction arrival rates under severe data contention, while considerably improving the success ratio compared to the tested baselines.