We investigate the performance implications of supporting transaction atomicity in a distributed real-time database system. Using a detailed simulation model of a firm-deadline distributed real-time database system, we profile the real-time performance of a representative set of commit protocols. A new commit protocol that is designed for the real-time domain and allows transactions to "optimistically" read uncommitted data is also proposed and evaluated. The experimental results show that data distribution has a significant influence on the real-time performance and that the choice of commit protocol clearly affects the magnitude of this influence. Among the protocols evaluated, the new optimistic commit protocol provides the best performance for a variety of workloads and system configurations.
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