JFR supports ObjectCountAfterGC events that provide a histogram of extant classes in the heap by size and count following each GC. This event isn't implemented for Shenandoah GC.

Ideally the impact of not enabling this event should be near zero, and enabling this event should minimally impact Shenandoah pause times. We expect that the extra work in collecting data for and emitting the event would slightly impact application performance via affecting the GC cycle.

The implementation of ObjectCount events is out of scope of this ticket and is pursued separately. Similarly, this ticket only covers the implementation of this event for Shenandoah. The implementations of ObjectCountAfterGC and ObjectCount events for Generational Shenandoah will be pursued in other tickets.

Submitter's note: This work is being done at AWS/Amazon by Patrick Fontanilla, who has signed the OCA and is awaiting his OpenJDK id and his JBS login. To prevent the ticket from being assigned to someone other than Patrick, pending the issuance of his JBS userid, I will assign this ticket to myself. Once Patrick's id is available, the ticket will be reassigned to him.