Cacti as others open source measurement collections systems rely the data storing and charting in the RRDTool software.
In our Cacti instances we are collecting measurements from 15000 different router/cmts interfaces, which includes common measures like bandwidth, cpu, memory and others not so common like SNR, Cable Modems in the upstream, modulation profile.
As the NOC is unable to watch and control this amount of charts, there is a nice functionality, not widely used, in the rrds: Aberrant Behavior Detection (ABD). ABD adds a set of measurements and algorithms that adapt to the seasonal trend of the chart and detects when a current value is too deviated from the expected value. You can read about the mathematical details here and here.
You can see some examples here:
|The classic bandwidth measurement|
|Cable Modems in the upstream channel|