Support ZGC in JvmGcMetrics

[shakuzen]

Similar to #1861 for ZGC. See the OpenJDK Wiki for ZGC for more information on it. In addition to GC pause time metric (jvm.gc.pause) which should already work, we should support the following when using ZGC:

• jvm.gc.max.data.size
• jvm.gc.live.data.size
• jvm.gc.memory.allocated

[crohit]

Hi @shakuzen - sorry to bug on this old post with this question, but I recently upgraded to zgc for a repo at work and am wondering what are the metrics available for zgc.

action:end_of_gc_pause,cause:proactive
action:end_of_gc_pause,cause:warmup

These are the only ones I see. Are there more metrics I should be seeing? Including any other causes and actions?

[shakuzen]

Are there more metrics I should be seeing? Including any other causes and actions?

Not until more actions and causes happen in your application after JvmGcMetrics is bound to a registry. The metrics are dynamically registered in response to GC notifications. Until GC events happen in your application, there won't be any metrics recorded for them. We do not register metrics for GC events until they happen. You could, for example, force a GC in your application (with e.g. System.gc() or JMX or jconsole) and see GC metrics recorded in response to that. Does that make sense and clear up what's happening?

[crohit]

Are there more metrics I should be seeing? Including any other causes and actions?

Not until more actions and causes happen in your application after JvmGcMetrics is bound to a registry. The metrics are dynamically registered in response to GC notifications. Until GC events happen in your application, there won't be any metrics recorded for them. We do not register metrics for GC events until they happen. You could, for example, force a GC in your application (with e.g. System.gc() or JMX or jconsole) and see GC metrics recorded in response to that. Does that make sense and clear up what's happening?

Ah yeah that clears up- Let me go back and look into this. Are there other notifications which are emitted on GC that I know I should look out for when a GC is run?

[shakuzen]

Are there other notifications which are emitted on GC that I know I should look out for when a GC is run?

We don't keep an exhaustive list because it is up to what the garbage collector has implemented, which can change between versions of the JVM. Unfortunately, I'm not aware of good documentation on this from each collector either.