Simulating distributed database systems is inherently difficult, as there are many factors that may influence the results. This includes architectural options as well as workload and data distribution. In this paper we present the DBsim simulator and some simulation results. The DBsim simulator architecture is extendible, and it is easy to change parameters and configuration. The simulation results in this paper is a comparison of performance and response times for two concurrency control algorithms, timestamp ordering and two-phase locking. The simulations have been run with different number of nodes, network types, data declustering and workloads. The results show that for a mix of small and long transactions, the throughput is significantly higher for a system with a timestamp ordering scheduler than for a system with a two-phase locking scheduler. With only short transactions, the performance of the two schedulers are almost identical. Long transactions are treated more fair by a two-phase locking scheduler, because a timestamp ordering scheduler has a very high abort rate for long transactions.