By default all metrics are assigned to the 'default' sampler.
The metrics.xml file allows assigning metrics to different samplers (e.g. 'high' to sample at higher rate, 'off' to disable sampling for a metric).
It's sometimes useful to set a metric sampler directly from command line, without editing the metrics.xml file.
This improvement allows setting a metric sampler via environment variable (with 'GS_METRIC_' prefix) or system property (with 'com.gs.metric' prefix).
For example, to disable all 'os' metrics, but sample 'os_memory' metrics at low rate: