The purpose of this study was to assess the performance of two database systems, PostgreSQL (relational) and MongoDB (non-relational), in handling data and their impact on application performance. The evaluation was conducted through a series of performance tests including read, write, delete, update, and aggregation operations on small and large datasets. Key metrics such as task completion time, response times were used for comparisons. Based on the results obtained during the experiments, it is difficult to definitively conclude which database system performs better, as both systems demonstrated advantages in different scenarios depending on the specific use case.