Some notes on the data models of various metrics collection systems. Performance Co-Pilot Performance Co-Pilot is a metrics collection and visualization system heavily inspired by SNMP. PCP originates in the systems monitoring world. PCP has a fairly rich vocabulary to describe metrics according to their type, semantics, dimensions and scale. type is the fundamental data type of the metric, eg. string, uint32, uint64, double, binary semantics describe the logical behaviour of a metric and can be counter, instant or discrete.