The timeseries databases I have used are good (and fast) at answering queries like "mean value of sensor_1 for every 10 min bucket". It can answer this fast. It

The timeseries databases I have used are good (and fast) at answering queries like "mean value of sensor_1 for every 10 min bucket". It can answer this fast. It can handle that some buckets have 1000 points in them, some have 0 or 1. It can calculate the moving average, again correctly with possible missing/unevenly spaced values. It can calculate the rate of change (the deriviative) fast. Often there are other time-related stuff in there as well, but I think the vast majority of use is fast calculation of "mean/max/first value of sensor(s) for X-second buckets".