A study is made of a known implementation of an optimistic concurrency-control algorithm for centralized database systems and improvements are suggested to the algorithm. The authors propose an implementation of an algorithm for the basic timestamp-ordering concurrency control in centralized database systems. The two algorithms are compared by simulation experiments. As expected, the optimistic approach is better for transaction mixes dominated by retrievals. For transaction mixes dominated by updates, the optimistic algorithm spends time performing operations that have a good chance of being voided by earlier conflicting operations. The authors expected the timestamp algorithm to be better in these circumstances but, this is not the case. They attribute this to the fact that transactions used in the experiments are short, and therefore the execution time lost due to an abort is small.>