1. A computer-readable medium having computer-executable instructions for causing a computer to perform steps comprising: creating a pessimistic duplication detection data structure for a parallel nested transaction; making an entry into the data structure for each pessimistic read in the parallel nested transaction; and when committing the parallel nested transaction, passing new pessimistic read locks to an immediate parent, and making an entry into a separate pessimistic duplication detection data structure of the immediate parent with synchronization between sibling transactions.