In monitoring, the term cardinality defines the number of unique time series stored in a time series database (TSDB). For example VictoriaMetrics single version needs 850MB RAM for 1 million unique time series and 4GB for 10 million series, but InfluxDB RAM needs 5GB for 1 million unique time series and reaches 9GB for 4 million unique time series, Prometheus starts from 6.5GB and stabilizes at 14GB, respectively.