The response-time distribution in a real-time database with optimistic concurrency control and exponential execution times

For a real-time shared-memory database with optimistic concurrency control, an approximation for the transaction response-time distribution is obtained. The model assumes that transactions arrive at the database according to a Poisson process, that every transaction takes an exponential execution time and uses an equal number of data-items uniformly chosen, and that the multiprogramming level is bounded. The analysis is based on a decomposition approach: results for the closed system with a fixed number of transactions are used to derive the responsetime distribution in the open system with Poisson arrivals. Numerical experiments that compare analysis with simulation indicate that the approximation for the throughput and the response-time distribution works well for the closed system. For the open system the approximation for the response-time distribution is useful if the load is not too high.