Default JVM metrics for GC pools, class load count, and descriptors

[realark]

For our APM JMX graphs we're interested in adding charts for specific GC pools (eden, old gen, etc), class load counts, and open file descriptors.

Couple of questions:

• Does it make sense to put these changes here (in core JMX)?
• Process-wise, does it work to propose built-in metric changes like this (through a PR)?

[olivielpeau]

Looks good to me 👍

We have to make sure the beans you're matching aren't already matched by existing includes (JMXFetch can only match a JMX attribute with at most one include conf, so if an attribute matches multiple includes, the first one that matches will determine the metric name and type that JMXFetch will emit for this JMX attribute). Had a cursory look at the existing default metrics and it looks OK 👍

To answer your questions:

• Adding these metrics in core JMXFetch means that all future versions of JMXFetch will collect these new metrics by default . If this was your intent then that makes perfect sense.
• Process-wise a PR is fine, any explanation you may have on why these metrics are important and should be collected by default would be interesting. Also, if these beans/attributes only exist on certain environments, that'd be interesting to document as well.

[realark]

Excellent, thanks! Yes it was my intent to add these to the default metrics.

These metrics will be used by APM to generate interesting JVM graphs and it seems like they are interesting to agent jmxfetch users as well.

[olivielpeau]

@realark we can merge this if you've confirmed it works well :)

[realark]

@olivielpeau Thanks! Yep it's working well! Just did some more end-to-end testing to verify: