The ever-growing hunger for high quality, up to date, and efficient datasets to be used in data-driven models and control systems lead to the diffusion of a number of database management systems specifically tailored to support operations on timeseries: Timeseries Databases. We focus on the systematic performance assessment of some of the most popular TSDBs available. To this end, we developed a tool specifically designed for the task at hand: SimpleMetric. By means of SimpleMetric, we measure the performance of the selected TSDBs in terms of the computational overhead introduced by a number of aggregation functions in a closed loop control scenario (i.e., monitoring and actuation).