Description of problem:
The resulting configuration after [1,2] only filters the main postmaster process:

(fname == "postmaster" && psargs ~ /-D/) ||

The main process does NOT show the resource consumption of the children processes, so using this config PCP would only show a partial picture of the postgres resource usage, inconsistent with the picture painted by top and the OS in general.

To report the correct resource usage, we need to include 'postgres' in the regex filter:

(fname == "postmaster" && psargs ~ /-D/) ||
psargs ~ /postgres/ ||

[1]: https://github.com/theforeman/foreman/pull/10815
[2]: https://issues.redhat.com/browse/SAT-41438

Actual behavior:
The postgresql resource usage reported by PCP is extremely lower than the one reported by the OS

Expected behavior:
The postgresql resource usage reported by PCP should be the same reported by the OS