To evaluate the performance of database applications and DBMSs, we usually execute workloads of queries on generated databases of different sizes and measure the response time. This paper introduces MyBenchmark, an offline data generation tool that takes a set of queries as input and generates database instances for which the users can control the characteristics of the resulting workload. Applications of MyBenchmark include database testing, database application testing, and application-driven benchmarking. We present the architecture and the implementation algorithms of MyBenchmark. We also present the evaluation results of MyBenchmark using TPC workloads.