Creates a new derived metric

Create a new derived metric, as defined by the pmAddDerived(3) metric interface. Derived metrics are associated with the named context, or a new context is created and returned in the result.

$ curl -s http://localhost:44322/pmapi/derive?name=blkio.avgsz&expr=disk.all.blktotal/disk.all.total | pmjson

This interface is one of the few that allows a POST to be used in place of a GET. In this case the HTTP POST request body may be used to provide one or more derived metrics specifications (all at once, across multiple lines, as a convenience).

$ curl -s http://localhost:44322/pmapi/fetch?name=blkio.avgsz&samples=2 | pmjson

Reference: pmAddDerived(3)