JFR Event for Full GCs

[Andrew Azores]

Hi all,

I'm looking into a JMC bug report [0] for adding a JFR rule to detect 
Full GC events. From what I could tell playing around with JMC and then 
by reading through the JFR and JDK GC sources, there does not seem to be 
an existing Full GC event, not any event that corresponds 1:1 with a 
full collection. There is the jdk.GarbageCollection event, but I don't 
see that any of its properties can be used to reliably indicate Full GC 
vs otherwise for all collectors (or at least both G1 and CMS as 
specified in the bug report). If this assumption is wrong please let me 
know and point me in the right direction.

If a JFR event does need to be added or modified to enable tracking full 
collection occurrences, would the preferred approach be to modify the 
jdk.GarbageCollection event with a field to denote the collection type, 
or to emit an entirely new event flagging a full collection? My personal 
leaning would be toward a new event marked experimental, but I defer to 
the experts.

Once I have guidance on the questions above I would be glad to prepare 
and submit a patch for your approval.

Thanks,

[0] https://bugs.openjdk.java.net/browse/JMC-5596

-- 
Andrew Azores
Software Engineer, OpenJDK Team
Red Hat