Optimistic similarity-based real-time concurrency control

Serializability is unnecessarily strict for real-time systems because most transactions in such systems occur periodically and changes among data values over a few consecutive periods are often insignificant. Hence, data values produced within a short interval can be treated as "similar" and interchangeable. This notion of similarity allows higher concurrency than serializability. The author discusses a similarity-based optimistic real-time concurrency control protocol. The protocol can outperform the similarity stack protocol (SSP) and does not rely on prior knowledge of worst-case execution time (WCET) and data requirements of transactions. Moreover, when similarity is not applicable, the protocol can be reduced to the ordinary optimistic protocol and accept serializable histories.