The semantics of commutativity in the execution of concurrent transactions

It is pointed out that a precise understanding of user process semantics is crucial to the design of schedulers for concurrent transactions. Although a scheduler that is at least sufficient to maintain database correctness must be designed, a more precise understanding of user process semantics will make it possible to identify and make use of additional properties maintained by the scheduler and assist in better understanding of how to improve the scheduling algorithm to allow a higher degree of user process concurrency. A precise formal model of these semantics, which is unique in that it incorporates any local processing required to produce an updated item in a function of the write request associated with that update, has been developed. This makes it possible to deal directly with the semantic content of schedules, rather than indirectly through commutativity rules.<>