Scott,
Your understanding is correct. As of APM version 9.1 and higher, there are now up to four new metrics under [font=Courier New]Agent Stats|Resources[font] which also populate the [font=Courier New]Resources[font] tab when you have an agent selected in the [font=Courier New]Metric Browser[font]. The four metrics are below:
[font=Courier New]Agent Stats|Resources:% CPU Utilization (Host)
Agent Stats|Resources:% Time Spent in GC
Agent Stats|Resources:Threads in Use
Agent Stats|Resources:JDBC Connections in Use[font]
These metrics are, in effect, like JavaScript calculated metrics - they are derived from other existing metrics and get reported to the same agent. The logic used to determine which existing metrics get used is defined in the [font=Courier New]ResourceMetricMap.properties[font] file. By default, the logic is as below:
[color=#008000]#CPU Utilization[color]
cpu.utilization.path.1=CPU:Utilization % (process)
[color=#008000]#Time Spent in GC[color]
memory.utilization.path.1=GC Monitor:Percentage of Time Spent in GC during last 15 minutes
[color=#008000]#Threads in Use[color]
threads.used.path.1=WebSpherePMI|threadPoolModule|WebContainer:ActiveCount
threads.used.path.2=WebLogic|JMX Aggregate|Thread Pool:Waiting Request Count
threads.used.path.3=Tomcat|ThreadPool|default thread pool:getCurrentThreadsBusy
[color=#008000]#JDBC Connections in Use[color]
connections.used.path.1=WebSpherePMI|connectionPoolModule:WaitingThreadCount
connections.used.path.2=WebLogic|JMX Aggregate|JDBC Connection Pool:Waiting Thread Count
If the specified metrics do not exist on the agent for any of the four resource metric types, the respective resource metric will not get generated. For example, if you had [font=Courier New]GC Monitor[font] disabled, you would not get the [font=Courier New]% Time Spent in GC[font] metric. Similarly, if your application server is not WebSphere, WebLogic, or Tomcat, you will not get the [font=Courier New]Threads in Use[font] metric. However, you
can add your own source metrics here, which can be very handy. Since many of the application I work with use Tomcat but do not use Tomcat's JDBC Connection pooler, I haved use a JavaScript calculator to sum up the number of JDBC backend connections to produce a [font=Courier New]JDBC:Connection Count[font] metric and then used that metric to tie it to the [font=Courier New]JDBC Connections in Use[font] metric. To my knowledge, wildcards are not supported in this configuration file, which is unfortunate and would have made that process much simpler.
On a related note, the Agent Stats node is also where the Sustainability metrics will appear, if you ever have to turn those on.